Advanced Accelerator Concepts 2026

26 Jul 2026, 16:00 → 31 Jul 2026, 16:00 US/Pacific

Luskin Conference Center, UCLA

The AAC26 workshop is a by-invitation biennial forum for intensive discussions on long-term research in advanced accelerator physics and technology. Since its inception in 1982, the AAC Workshop has become the principal US meeting for advanced particle accelerator research and development with strong international participation. We are anticipating over 250 scientists and research leaders in particle-beam, laser, and plasma physics to participate in this year’s meeting. This research supports the development of capabilities for the basic sciences, from photon science to high energy physics, as well as the development of compact accelerators for industrial, medical and security applications.

The Workshop is organized by UCLA Department of Physics and Astronomy and will take place in Los Angeles, CA from July 26-31, 2026 at the Luskin Conference Center located on the UCLA campus.

Program at a Glance (Preliminary)

Sunday 26 July

17:30 Welcome Reception

Monday 27 July

Invited Talks: Plenary

1 Very high energy electrons from multi-Petawatt LWFA in a transitional regime

We present results from the ELI50122 campaign using the ELI-NP 10 PW beamline. We observed multi-PW-driven LWFA in a transitional regime where PWFA takes over the high-energy boosting stage. Using a nitrogen-doped helium gas at electron densities of 4-6 × 10¹⁷ cm⁻³ favored this transition, demonstrating beams of multi-nC charge with a clear dependence on the N₂ concentration.
The experimental results show energies of 8-10 GeV in a 15.5 cm gas cell and energy boosting following a switch to a 28 cm long acceleration medium. When the electron beam driver takes over the acceleration, we observe electron bunches peaking as high as 17.1 ± 2.0 GeV, with the tail extending beyond 20 GeV. The bunch had 22.1 ± 5.5 pC charge confined to a divergence below 1 mrad.
Total beam charge in this experiment reaches 3 nC above 2 GeV with >100 pC above 10 GeV in selected cases. The results represent a significant advance over past achievements in this field, doubling the maximum energy and obtaining 1.5-1.9× higher peaks for the bunches.

Speaker: Calin Hojbota (The University of Texas at Austin)

2 Plasma Injector for Synchrotron Lightsources

DESY is pursuing an ambitious laser-plasma injector option for its future PETRA IV synchrotron. The plasma injector will deliver 6 GeV electron beams for direct injection into the ring, offering a significant reduction in footprint and energy consumption.

We will present the conceptual design and development roadmap and discuss technology challenges including drive laser and plasma accelerator performance. Furthermore, we will discuss experimental steps towards realization: this includes the recent demonstration of active energy compression, that delivered sub-permille energy stability beams already suitable for injection at lower energies, and progress on a prototype plasma injector for the PETRA III synchrotron.

Speaker: Andreas Maier (DESY)

3 Recent Advances in Plasma Wakefield Acceleration at FACET-II

At the FACET-II national user facility, plasma wakefield acceleration (PWFA) experiments are advancing beam-driven concepts towards application-relevant performance. Using a 10 GeV, high brightness electron beam and a variety of plasma sources, we demonstrate stable, multi-GeV acceleration of externally and internally injected witness beams. In two-bunch linac operation with a 40 cm Li vapor plasma source, we achieve witness energy gains exceeding 5 GeV with sub‑percent relative energy spread and drive‑to‑witness energy transfer efficiencies greater than 10%. Machine learning-enabled beam tuning is used to improve beam density and transverse alignment between bunches, enhancing energy-transfer efficiency and limiting emittance growth. We will also report on the operation of a plasma brightness transformer using density downramp injection to simultaneously boost the energy and brightness of an electron bunch injected from the plasma, and other recent results.

Speaker: Doug Storey (SLAC National Accelerator Laboratory)

10:15 Coffee break

Invited Talks: Plenary

4 Radiation generation and applications from laser-plasma accelerators

Relativistic electron beams from compact Laser Plasma Accelerators (LPAs) have unique and favorable properties that can be transferred to LPA-driven secondary radiation sources. Properties include the point-like nature of the radiation source, femtosecond duration, low emittance, high energy for deeper penetration, and large flux per shot. Combined with high-repetition-rate laser drivers and overall system compactness, this combination of characteristics can provide application capabilities unavailable through other means.

In this talk, I will focus on several key particle and photon products from laser-plasma accelerators, namely the electron beams themselves, muons from a converter target, betatron-oscillation X-rays, laser-scattered gamma rays, and undulator-based free-electron laser emission. The small source size and emittance ensure advantageous high-spatial-resolution lens-less imaging and tight focusing for charge delivery applications. The femtosecond duration enables high-temporal-resolution blurring-free imaging as well as applications where high peak-currents and near-instantaneous charge delivery are of interest. The high electron energy enables deep penetration and efficient conversion to, for example, muons that remain highly directional. In the context of emerging high-repetition-rate laser technology and deployable system engineering, I will highlight the community's efforts to field non-perturbative diagnostics and incorporate active stabilization concepts that further enhance robustness and application impact.

This work is supported by the DOE Office of Science, High Energy Physics (HEP) and Basic Energy Sciences (BES), under Contract No. DE-AC02-05CH11231, by the Defense Advanced Research Projects Agency (DARPA), and by the U.S. DOE National Nuclear Security Administration Defense Nuclear Nonproliferation R&D (NA-22).

Speaker: Jeroen van Tilborg

5 Towards dephasingless LWFA

Laser-wakefield accelerators (LWFAs) have demonstrated the ability to generate high-quality, monoenergetic electron beams. Yet, efforts to achieve higher electron energies are hampered by electron dephasing and beam diffraction. One promising approach to mitigating these limitations is the use of structured light to control the on-axis propagation velocity within LWFAs. This method promises an improved balance of extended acceleration distances and strong accelerating gradients.

In this talk, we report the first experimental observation of wakefields driven by such structured-light beams as well as the first experimental evidence of the mitigation of dephasing in electron acceleration. Spatiotemporally engineered laser pulses are focused using a specialized mirror to produce a quasi-Bessel beam, and the resulting wakefields are directly measured using femtosecond relativistic electron microscopy. We experimentally demonstrate control over the on-axis propagation velocity of the wakefield and follow its evolution throughout the focal region. We investigate how targeted spatiotemporal modifications affect both the wakefield structure and its propagation velocity. Finally, we present the first successful acceleration of electrons using these wakefields, demonstrating partial mitigation of dephasing.

[1] C. Caizergues et al. “Phase-locked laser-wakefield electron acceleration,” Nat. Photonics. 14, 8 (2020)
[2] J.P. Palastro et al. “Dephasingless laser wakefield acceleration,” Phys. Rev. Lett. 124, 134802 (2020)
[3] A. Liberman et al.,“Direct Observation of a Wakefield Generated with Structured Light,” Nat. Commun. 16, 10957 (2025)
[4] A. Liberman et al.,“First Electron Acceleration in a Tunable-Velocity Laser Wakefield,” under review. (https://arxiv.org/abs/2509.21098)
[5] A. Liberman et al.,“Probing Flying-Focus Wakefields,” under review. (https://arxiv.org/abs/2510.16950)
[6] A. Liberman et al., “Use of spatiotemporal couplings and an axiparabola to control the velocity of peak intensity,” Opt. Lett. 49, 814-817 (2024)

Speaker: Aaron Liberman (Weizmann Institute of Science)

Aaron_AAC_2026.pptx

6 Sub-GV/m gradient in Short-Pulse X-Band Photogun: From First Demonstration to Recent Results and Future Developments

Normal-conducting accelerating structures capable of supporting GV/m-scale electric fields offer a compelling pathway toward compact accelerator systems. Achieving such fields in photocathode RF guns is equally essential for the production of high-brightness electron bunches. Our group has recently demonstrated ~0.4 GV/m peak electric fields on the photocathode surface of an X-band (11.7 GHz) photoemission gun (Xgun) powered by ultra-short (~9 ns) RF pulses. In this work, we present the latest experimental progress, including beam characterization through slice-emittance measurements and longitudinal phase-space diagnostics. We also discuss a novel hybrid accelerating-structure design being developed for the Xgun beamline upgrade, together with ongoing and future directions toward the high-energy beam generation at the level of 100 MeV.

Speaker: Gongxiaohui Chen (ANL)

12:15 Lunch

A1-Working Group # 1

7 Next-Generation High-Repetition-Rate Lasers for Laser–Plasma Accelerators and Secondary Sources

Laser–plasma accelerators (LPAs) are rapidly emerging as compact and versatile drivers for applications in science and industry. However, their broader adoption is fundamentally constrained by the limited availability of laser systems capable of simultaneously delivering high pulse energy and high repetition rates.

Amplitude has pioneered this field with a 10TW 100 Hz Ti:Sapphire system installed already in 2013 at LP3 laboratory. This unique laser drives a table-top high brightness X-ray plasma source, and demonstrated phase-contrast imaging or X-ray diffraction. Building on this foundation, a new concept for a 1 J, 100 Hz Ti:Sapphire driver is being currently developed. It combines a CPA architecture seeded by an industrial-grade Yb-laser–pumped OPCPA front-end, with amplification stages pumped by a newly designed diode-pumped Titan-C laser. Amplifier thermal management is addressed through cryogenic cooling, while solutions to circumvent thermal effects in the compressor are studied in collaboration with the HZDR and LP3 groups. Additionally, the development of multi-J pump lasers designed for 100Hz and more prepares the advent of PW class lasers for future accelerator facilities.
In parallel, Amplitude explores the use of Yb-based lasers as compact, high-average-power drivers for industrial applications. We will present our latest results, achieving 0,6TW at 1kHz by compressing 20mJ 350fs pulses down to 23 fs using a multipass cell.

Speaker: Kaikai Zhang (Amplitude Laser)

8 Coherent Beam Stacking Enabled Compact, Energy Scalable, and Several Optical Cycle Capable Ultrashort Pulse Post-Compression for the Next-Generation LWFA Drivers

Gérard Mourou Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Blvd., Ann Arbor, MI 48109, USA

Laser-wakefield plasma accelerators (LWFA) promise compact sources of highly energetic electrons and photons, but for their practical use they need efficient and high repetition rate laser drivers. The current standard is the Ti:sapphire CPA system, which can produce multi-J pulses with bandwidths supporting ~30 fs pulses, but it has low wall plug efficiency (WPE) and ~Hz repetition rates. Fiber laser systems can operate with high WPE at 10’s of kHz and are scalable to high energies and powers using spatial and temporal coherent combining but have bandwidth’s sufficient for only 50-100fs pulses. Additional spectral combining can extend this bandwidth, but by increasing overall complexity of the fiber laser driver. We propose a Nonlinear Coherent Beam Stacking (N-CBS) technique, which could enable achieving several cycle pulses comparable to those of Ti:sapphire, while maintaining multi-kW power and the multi-J energy scalability of coherently combined fiber laser arrays with only a minor increase in the overall complexity of the system and in a compact footprint.
Coherent Pulse Stacking Amplification (CPSA) is critical for reducing spatially-combined fiber laser array sizes by approximately two orders of magnitude. In demonstrated CPSA systems [1] a stacking-burst of stretched pulses extracts nearly-all stored energy from the final amplification stage and is temporally combined (using GTI cavities) into a single stretched pulse for compression to the bandwidth-limit at the system output.
In this paper we show that using a newly discovered Coherent Beam Stacking (CBS), which is a spatial-domain analog of the time-domain Coherent Pulse Stacking (CPS), it is possible to achieve orders-of-magnitude increase in pulse energies with multi-pass cell (MPC) based nonlinear post-compression down to 25-30 fs, while maintaining a compact, 1-3 meter footprint.
Using a specially-designed phase mask, an incident Gaussian beam at the input into an MPC can be transformed into a multi-focal pattern in the Fourier plane of the MPC front mirror. The resultant field contains a pattern of N coherent, equal amplitude, high intensity focused regions reducing the intensity per region by a factor of N for the same pulse energy, while achieving large on-mirror spot sizes. Each roundtrip in, e.g. a gas filled Herriott cell [2], reproduces this pattern in the waist-plane of the optical cavity, and can be transformed back into a diffraction-limited Gaussian beam with another phase mask placed at the MPC output, after a desired number of roundtrips. Because this phase-mask transformed field propagates in an MPC as a single field, all independent random perturbation are homogenized across the multitude of all focal spots, and hence eliminates a need to coherently control their recombination into a single Gaussian beam at the MPC output.
Therefore, this scheme can greatly increase energy handling capability of MPC post-compression, with preliminary results indicating homogeneous spectral broadening of joule level energies in meter length cavities, which can subsequently be compressed using chirped mirrors to durations much shorter than fiber gain bandwidth supports. Implementing this scheme needs only a minor increase in the overall CPSA system complexity. Furthermore, it can be used for spectral broadening of any laser-driver platform, and thus fulfills the general need for such energy scaling-up of a nonlinear post-compression scheme, which was identified in [3].

[1] Rainville, A. et al., (2024). Near-complete extraction of maximum stored energy from large-core fibers using coherent pulse stacking amplification of femtosecond pulses. Optica, 11(11), 1540-1548. doi:10.1364/OPTICA.533803

[2] Kaumanns M, Pervak V, Kormin D, Leshchenko V, Kessel A, Ueffing M, Chen Y and Nubbemeyer T 2018, Multipass spectral broadening of 18 mJ pulses compressible from 1.3 ps to 41 fs, Opt. Lett. 43, 5877

[3] M. F. Kling et al., Roadmap on basic research needs for laser technology, J. Opt. 27 013002 DOI 10.1088/2040-8986/ad8458

Speaker: Tayari Coleman (University of Michigan)

9 Design and progress of a 150 mJ, 40 fs, 5 kHz fiber-laser accelerator driver

Fiber lasers have outstanding features including power handling, efficiency, and beam quality. Spatial and temporal combination of ultrafast fiber lasers provides pulse energy and power scaling (up to 10 J, 100 kW), a promising solution for driving next-generation kilohertz plasma accelerators and their secondary radiation sources, as well as for enabling new capabilities in beam diagnostics, manipulation, and electron removal for radiofrequency accelerators. We are building an architecture that integrates coherent pulse combining in space, time, and spectrum simultaneously, which also provides pulse duration reduction (to as short as 30-40 fs) besides energy/power scaling, critical to applications requiring short pulses (e.g. plasma acceleration).

Here we present the design and development progress of a multidimensionally combined fiber laser that will deliver 150 mJ energy, 40 fs duration, 5 kHz rep-rate, 1 kW average-power pulses, including overcoming challenges due to broad bandwidth in seeding, amplification, gain narrowing/saturation, combining, dispersion and compression.

We completed the system frontend and a high power amplification chain, where laser pulses are burst-modulated, spectrally broadened, stretched, split into three spectral channels, and amplified through multiple single-mode and large-core Yb fiber amplifiers with distributed spectral filtering. Programmable pulse shaping was implemented in each spectral channel, and its feedback optimization was achieved. We developed record large core (85 µm) monolithically integrated fiber amplifiers, and demonstrated record energy amplification (8 mJ) from a monolithically integrated amplifier. In each spectral channel, we will further install a final array of 9 high power fiber amplifiers (the same as the existing type tested at 8 mJ).

In proof-of-principle tests, we demonstrated record short pulses (42 fs) from spectrally combined Yb fiber lasers and record broad bandwidth (supporting ~50 fs) in temporal stacking 10 fiber-amplified laser pulses. An FPGA-based control system has been implemented in the 150 mJ system for laser and combining controls, and machine protection. After the final fiber amplifier arrays are installed, the amplified pulses will be sequentially combined by a diffractive spatial combiner, a dichroic-optic spectral combiner, and a cascaded-cavity temporal stacker, all being fabricated, and finally compressed by an out-of-plane, multilayer dielectric grating compressor.

This work is supported by DOE Office of Science HEP and ARDAP, and Moore Foundation.

Speaker: Tong Zhou (Lawrence Berkeley National Laboratory)

10 Ultrashort Pulse Generation and High Power Machine Protection in a Fiber Laser for Advanced Accelerator Applications

The next generation of laser-plasma accelerators (LPAs) require a novel laser architecture to support multi-kHz and multi-kW operation for scientific, medical, industrial and security applications. Combining pulsed fiber lasers spatially, temporally, and spectrally provides a viable path to high peak and high average power. Such lasers can also upgrade beam diagnostics, shaping, and stripping in radiofrequency accelerator facilities. To achieve ultrashort pulse durations as needed for applications, e.g. LPA drivers, we developed broadband spectral combining and comprehensive system dispersion compensation methods. In addition, to protect high power fiber amplifiers from damage during operation interruption, we developed a multilayer, high speed FPGA-based protection system.

We have built a three-spectral-channel, multi-stage fiber chirped pulse amplification (FCPA) laser system aimed at combining these spectral channels and achieving ~40fs compressed pulses after ~70dB gain. To reach transform-limited pulse durations, we have modeled the systemic dispersion at various orders from pulse propagation through a fiber-based stretcher, fiber amplifiers, and a grating compressor, and designed compensation schemes. We have also built an automated spectral phase mapping and optimization loop using programmable pulse shapers, and further achieved optimally compressed pulses from one spectral channel. We have demonstrated phase-locking of all three spectral channels using FPGA-based feedback controls, and are currently investigating coherent spectral combination and pulse compression.

Unwanted changes in seeding and pump conditions of high power laser amplifiers can result in damage to the system. We have designed and implemented an FPGA-based, multilayer, distributed protection system, via rapidly sensing errors in signal amplitude, duration, and timing, and stopping seed pulses and pump lasers, critical for multi-spectral-channel high power laser amplifier operation.

Work supported by the U.S. DOE, Office of Science, Office of High Energy Physics, under Contract No. DE-AC02-05CH11231, and the Moore Foundation, under Grant No. 10631.

Speaker: Mahek Logantha (UC Berkeley/Lawrence Berkeley National Lab)

11 100mJ Spatially and Temporally Combined Femtosecond Fiber Laser System Enabling Next Generation Laser Plasma Accelerators

Next generation laser wakefield accelerators (LWFA) will require TW-PW peak power laser drivers operating at multi-kHz repetition rates [1]. This translates to 10s -100s kW of average power – orders of magnitude beyond current state-of-the-art LWFA drivers based on Ti:sapphire CPA. It is recognized that one of the most promising pathways for achieving this level of laser-driver performance is coherently combined femtosecond fiber laser systems. Over last several years we have demonstrated key technological milestones to enable this approach: 85µm core chirally-coupled-core (3C) fibers and their potential for monolithic integration as a high-energy amplifier-array scaling platform, coherent pulse stacking amplification (CPSA) as a key enabler in ~100-times reduction of system size and complexity, full stored energy extraction at ~10mJ per amplification channel using this CPSA technique and 85µm 3C fibers, and simultaneous compatibility of time-domain (CPSA) and spatial-domain coherent combining at ~10mJ per channel.

Based on these advances we have recently built a 12-channel coherent beam combining (CBC) and CPSA system for reaching a 100-mJ combined pulse energy milestone, the energy range suitable for driving LWFA electron acceleration experiments. At this Workshop we will report on our ongoing power and energy scaling experiments with this system, which has already become the highest energy fiber laser CBC system demonstrated. Furthermore, we will report on our future pathway of demonstrating LWFA, which to achieve with this energy level requires ~30fs duration pulses. Presently, the system delivers ~300fs pulses, with the potential for reaching <100fs after optimization. To reach the required ~30fs we are developing a novel multi-pass cell (MPC) based post-compression technique, which is capable of being scaled to Joule level pulse energies, and which thus offers a pathway to the first fiber-driven LWFA electron acceleration experiments.

[1] “Rerport of the basic research needs workshop on laser technology,” https://science.osti.gov/- /media/ardap/pdf/2024/ Laser-Technology-Workshop-Report_20240105_final.pdf

Speaker: Christopher Pasquale (University of Michigan)

12 Update on the LWIR Laser Capability at ATF

The 5-TW long-wave infrared (LWIR) laser at the Accelerator Test Facility (ATF) has been successfully recommissioned following a nearly two-year shutdown undertaken to upgrade the facility to modern safety and operational standards. The system is now ready for the restart of the ATF user program, featuring improved beam quality achieved through the implementation of BaF$_2$ amplifier windows, which offer significantly enhanced environmental stability and mechanical robustness compared to the previously used NaCl optics.

We also discuss a pathway for delivering sub-picosecond pulses to selected experiments via post-compression of the 2-ps output from the CPA CO$_2$ amplifiers. In addition, ongoing R&D efforts toward achieving operation in the 25-TW, 100-fs regime are presented, along with a conceptual vision for a next-generation, optically pumped LWIR facility.

Speaker: Mikhail Polyanskiy (Brookhaven National Laboratory)

Polyanskiy_AAC.pptx

A2-Working group # 2

13 Efficient proton acceleration in near critical density targets

Improved control of high intensity laser parameters, in particular with respect to temporal pulse contrast and spatio-temporal couplings, enabled the exploitation of proton acceleration mechanisms surpassing target normal sheath acceleration. Ultra-thin and near critical density targets provide access to cascades of acceleration regimes that boost energies well beyond 100 MeV [1], but also yield unprecedented laser energy to proton energy conversion. This presentation focuses on experiments performed at the DRACO PW laser at HZDR in this regime. It highlights recent progress made with cryogenic hydrogen jets [2] where of the order of 50 MeV proton beams could be generated with Joule-level few 10 TW pulses on thickness optimized flat hydrogen targets [unpublished] at a laser limited repetition rate of 1 Hz.

[1] T. Ziegler et al., Nature Physics 20, 1211 (2024)
[2] M. Rehwald, et al., Nature Communications 14, 4009 (2023)

Speaker: Ulrich Schramm

14 Enhanced acceleration of high-energy proton beams from laser-driven stochastic 3D printed microstructures

Laser-driven ion acceleration in plasma is being explored as a source of ion beams with high peak current that can be useful in many fields of science and medicine. Recently, we introduced a new target platform using two-photon polymerization (2PP), 3D laser-printed multilayered microstructures with average densities lower than solid that are relatively insensitive to the laser prepulse. In a series of experiments at the OMEGA EP facility, we studied petawatt 1-m laser-driven ion acceleration in such 3D-printed wire microstructures [1]. Two types of microstructured targets- consisting of either a multilayered log-pile or a stochastic arrangement of one micron diameter wires are used. Although both demonstrate a higher energy and yield proton acceleration compared to thin solid-density foil targets, stochastic microstructures systematically produced higher proton energies and particle yields. The key advantage of a relatively thick 10-20 m stochastic wire structure is efficient coupling of the laser into a flux of hot electrons in the target's front and formation of an overdense, wire-related, microplasma surrounded in voids by a low-density plasma sustaining sheath field at the back on a few picoseconds time scale. This is supported by observation of additional electron heating in such a hybrid plasma resulting in generation of a stream of hot electrons in forward direction with an electron temperature, Thot up to 50MeV and with the maximum electron energy reaching 150 MeV much above the ponderomotive energy. We will discuss the results of optimization of stochastic 2PP-3D multilayer microstructures aiming to reach record proton energies in 5x1020 W/cm2 peak intensity laser-plasma interactions. This approach may become a viable alternative to nanofoils in generation of energetic ion beams that doesn’t require high-nanosecond/picosecond contrast laser pulses.
[1] S. Tochitsky et al, High-energy Ion Beams Generated with High Efficiency Using Laser-driven 3D Microstructures, Sci. Rep., (2025) 15, 37860.

Speaker: Sergei Tochitsky (UCLA)

15 Significant Increase in the Number of Energetic Protons with Two Hot Temperatures of 1 and 4 MeV During the Interaction of an Ultra-Intense Laser with a Foam Target Near the Critical Density and Coulomb piston signature.

Significant Increase in the Number of Energetic Protons with Two Hot Temperatures of 1 and 4 MeV During the Interaction of an Ultra-Intense Laser with a Foam Target Near the Critical Density and Coulomb piston signature.

G. Malka,1 P. Raczka,2 H. Larreur,1,3,4 D. Molloy,4,5 Y. Fukuda,6 K. Batani,2 D. Singappuli,1 Bing Liu,7 Dong Ao,7 Wei Kang,8 S. Pikuz,3 A. Martynenko,9 N. Borisneko,10 T. Pikuz,11 W.Nazarov,12 G.Giuntelli,5 T. Hayakawa,5 A. Yogo,6 Z. Lan,6 Y. Arikawa,6 A. Morace7, D.Mancelli, 1,14,15 A. Aliverdiev,13 D. Batani,1
1) Université de Bordeaux, CNRS, CEA, CELIA, Unité Mixte de Recherche 5107, Talence 33400, France
2) Institute of Plasma Physics and Laser Microfusion, Hery 23, 01-497 Warszawa, Poland
3) Departamento de Física Fundamental, Universidad de Salamanca, 37008 Salamanca, Spain
4) HB11 Energy Holdings Pty, Freshwater 2096, Australia
5) Centre for Light-Matter Interactions, Queen’s University, Belfast, Belfast BT7 1NN, United Kingdom
6) Institute of Laser Engineering, Osaka University, 2-6, Yamadaoka, Suita, Osaka, Japan
7) ENN Fusion Technology R&D Center (ENN-FTRC), Langfang, China
8) HEDPS, Center for Applied Physics and Technology, Peking University, Beijing 100871, China
9) Plasma Physics Department, GSI Helmholtzzentrum fur Schwerionenforschung, 64291 Darmstadt, Germany
10) Lebedev, Russia
11) Institute for Laser Technology, 2-6, Yamadaoka, Suita, Osaka, Japan
12) Wigen Nazarov
13) IGRRE JIHT RAS, Makhachkala, Russia
14) Institute of Plasma Physics and Lasers-IPPL, University Research and Innovation Centre, Hellenic Mediterranean University, 74100 Rethymno, Greece
15) Department of Electronic Engineering, Hellenic Mediterranean University, 73133 Chania, Greece

Key words: proton acceleration, high intensity lasers, low density foams, TNSA
ABSTRACT

We present the experimental results of proton acceleration obtained at the LFEX laser facility in Osaka, 1 kJ, 1 ps, I > 10¹⁹ W/cm², with foam targets of 3, 8, and 16 mg/cc and 200 m thick, as well as with thin foil targets. For the 3 mg/cc foams, the proton distribution, emitted on the back side of the target, exhibits two hot temperatures: one of 1 MeV for energies below 8 MeV, and one of 4,5 MeV for energies up to 20 MeV. The novel result is that the number of protons increases by more than a decade, and significantly increasing the conversion efficiency from laser energy to the proton beam. By increasing the angle of incidence of the laser beam on the target from 0 to 15°, we observe that the proton beam remains perpendicular to the back face of the target. We discuss the competition between the different acceleration processes involved, such as TNSA and RPA. In the case of thin foil (6 m CH), the formation of energy bunches in the proton spectra which are due to the interplay between the protons and the highly charged carbon ions (mostly C6+) which are also accelerated by the lasers. These finding are coherent with theoretical formulation predictions that the carbon ions act as a “Coulomb piston” on protons.

Speaker: gerard malka (UNIVERSITE DE BORDEAUX)

16 Generation of deuteron beams from laser-driven thin foils for neutron radiography

Thin deuterated plastic foils have been used in medium-scale laser facilities, such as the Trident and Phelix laser facilities, for production of deuteron beams which are ultimately used for neutron generation. Here we produced deuteron beams from CD sub-micron thin films using a 0.5kJ sub-ps laser at the Omega-EP laser facility. Deuteron yield is estimated to be ~5e+12 d/shot and ~ 2.3e+13 d/sr for a foil target of thickness ~700-800nm. We will compare our results with deuteron beams from other experiments using thicker films or foam targets, as well as neutron generation from such beams based on the pitcher-catcher scheme and from other alternative concepts for neutron radiography applications.

Speaker: Chengkun Huang (Los Alamos National Lab)

17 Recent developments of a laser-driven ion acceleration beamline at SIOM

Laser driven ion acceleration provides a route to achieve high quality ion beams, which could be superior for specific applications. In this talk I will present recent development of a laser driven ion acceleration beam line based on a homemade table-top 200 TW laser system at Shanghai Institute of Optics and Fine Mechanics (SIOM). Our major motivation is the potential application of such pulsed ion sources.

Speaker: Prof. Jianhui Bin (Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences)

18 Proton Beam Focusing in Low Density Plasma from High-Repetition-Rate Liquid-Sheet Targets

High-intensity lasers can accelerate protons from solid targets via target normal sheath acceleration (TNSA). These beams possess short pulse durations and low emittance, with potential applications in radiobiology, radioisotope production and warm dense matter. However, their inherently large divergence (10’s of degrees) and the challenge of achieving multi-Hz operation need to be addressed. Building on a Gemini TA2 experiment in which proton focussing was observed in a low-density vapour from a liquid-sheet target, this presentation explores the impact of laser temporal shape, plasma profile and particle beam properties on proton beam size, presenting both simulation and experimental results.

Speaker: Jimmy Weeks (Queen's University Belfast)

A3-Working group # 3

19 Multipole Expansion and Delta-Sheath Model in Flat-Beam PWFA: Comparison with PIC Simulations

Flat-beam plasma wakefield acceleration can produce asymmetric blowout cavities, requiring theoretical descriptions beyond the usual cylindrically symmetric blowout model. We present a simulation comparison of a multipole expansion for an asymmetric delta-sheath blowout model in flat-beam plasma wakefield acceleration. From simulation data, we extract the multipole moments of the wake potential together with the corresponding delta-sheath boundary. The accuracy of the truncated expansion is quantified by reconstructing electromagnetic fields inside the blowout cavity and evaluating their residuals against the simulation data. We find that the quadrupole approximation captures the dominant elliptic deformation and remains useful as an analytically tractable working model. These results provide numerical support for future self-consistent modeling of blowout cavities and their associated wakefields.

Speaker: Yunbo Kang (University of California, Los Angeles)

20 Progress of the E310 - Trojan Horse-II experiment at SLAC FACET-II

The E310 - Trojan Horse II project aims to demonstrate a plasma wakefield acceleration (PWFA) injection scheme capable of producing stable, ultra-low emittance, and thus high-brightness electron bunches. Current experimental investigations focus on the Trojan Horse injection scheme not only in transverse but also in collinear geometry, thereby extending earlier findings at SLAC FACET-I, where the feasibility of the 90-degree plasma photocathode injection was successfully demonstrated using the multi-kA drive beams only available there. The now ongoing experimental efforts at SLAC FACET-II focus on validating the underlying ionization and injection processes under realistic operating conditions.
We present recent preparatory experimental results, including successful ionization studies and stability scans performed with the upgraded experimental setup. These experimental runs substantiate reliable operation of the laser ionization and provide insight into the parameter stability for controlled injection. In addition, different strategies for pre-ionization and their impact on injection stability will be discussed. Finally, we outline the next experimental steps toward achieving full collinear Trojan-Horse injection and controlled witness-bunch generation.

Speaker: Natascha Thomas (Heinrich Heine University)

21 New light on wakefield longevity

The time for a stationary plasma to recover its original state after a wake is excited determines the repetition rate and luminosity of plasma-based colliders. Recent measurements showed that, after exciting one wake with an impulse of $\sim 0.5$J energy in plasma of density $n_e\sim10^{16}\,$cm$^{-3}$, a second wake yielding indistinguishable beam properties could be excited at time delays ranging from 60ns to $<1$ns, depending on plasma species, suggesting a potential for repetition rates ranging from tens of MHz to $\sim 1$GHz.
Here, we report complementary experiments carried out at SLAC’s Facility for Advanced Accelerator Science and Experimental Tests (FACET-II) in which, instead of generating a second wake, we employed a sub-ps, time-delayed, grazing-incidence optical probe pulse to detect remnants of the original excitation. Moreover, we excited wakes with impulses up to 20 J energy, 40x more strongly than in previous experiments, and examined the response of plasmas of three different species (hydrogen, lithium, argon). The results show that wake remnants are detectable at time delays ranging from $\sim 0.1\,\mu$s in hydrogen to several tens of $\mu$s in argon. These long-lived structures will contribute to cumulative heating, and thus are likely to limit plasma accelerators to sub-MHz repetition rates.

Speaker: Jason Brooks

22 Resonant Excitation of Plasma Wakefields with a Train of Relativistic Particle Bunches

In the context of plasma wakefield acceleration, resonances can be exploited to generate large-amplitude wakefields, using a train of relativistic particle bunches with frequency content close to the plasma electron frequency, to accelerate a trailing bunch.
We show with experimental results and numerical simulations that the wakefields driven by individual successive bunches in overdense plasma superpose linearly, and that their amplitude increases along the train, under optimal coupling with plasma density oscillations. We also demonstrate that a train of bunches with increasing charge can be used to enhance the transformer ratio of the acceleration process, hence improving the energy transfer efficiency [1].
We will discuss future experiments to demonstrate the resonant scheme in the non-linear regime.

[1] L. Verra et al., Phys. Rev. E 112, 045205 (2025)

Speaker: mario galletti (Laboratori Nazionali di Frascati - INFN)

23 Transverse control and optimization for plasma wakefield acceleration

Emittance preservation is one of the biggest challenges in beam-driven plasma wakefield acceleration (PWFA), demanding extremely precise control of the transverse aspect of the electron beam. We will talk about recent experimental progress in transverse control and optimization for the PWFA experiment at FACET-II in order to demonstrate a collider-quality PWFA stage. We will talk about various novel diagnostics: slice BPM dispersion measurement, beam reconstruction and optimization, etc. We will talk about the application of ML-based optimization based on beam-only measurements and plasma performance.

Speaker: Yiheng Ye (SLAC/Stanford)

24 A Discharge Capillary Plasma Source for Wakefield Acceleration Research at FACET-II

A new discharge capillary plasma source is being developed for the FACET‑II National User Facility at SLAC National Accelerator Laboratory. The FACET accelerator delivers 10 GeV electron beams with nanocoulomb charge and peak currents of 30-100 kA for advanced accelerator
research.
The capillary discharge plasma source provides operational advantages over existing plasma sources at FACET-II. The device is easily operable and highly tunable, which enables more beam time for experiments. Specific experimental goals include emittance preservation in a plasma wakefield accelerator, high transformer ratio acceleration, ionization injection, and photon acceleration.
A laboratory setup replicating the planned FACET‑II installation is currently under construction. This configuration allows offline plasma characterization (without the electron beam) to map key plasma parameters and study their dependence on controllable inputs.
Plasma generation is achieved using a capacitive discharge circuit capable of delivering up to 35 kV and 500 A to a capillary typically 50 mm in length, with the option to adjust the length for specific experimental needs. Helium gas is supplied through a continuous flow regulated by two
mass‑flow controllers. An alternative gas supply configurations and species are also under consideration.
Plasma density profiles and their temporal evolution are measured both along and across the capillary using Stark broadening of helium emission lines in the visible range (587.56 nm, 501.57 nm, and 447.15 nm). Plasma temperature estimates are obtained from intensity ratios of nearby emission lines or from line‑to‑continuum ratios. An auxiliary interferometric system is planned to validate the spectroscopy measurements.
This report provides an overview of the project, describes the diagnostic methods and instrumentation, outlines design considerations, and presents initial experimental results.

Speaker: Dr Konstantin Kruchinin (SLAC National Accelerator Laboratory)

A5-Working group # 5

25 Monte-Carlo modeling and experimental investigation of photoemission from CsTe semiconductor photocathode under high fields

Beam brightness can be enhanced with high gradient operation in photocathode guns. Such high gradient guns, such as the L-band gun at the Argonne Wakefield Accelerator (AWA) facility and the C-band high gradient gun being commissioned in the CARIE project at Los Alamos National Laboratory, are also typically equipped with semiconductor photocathodes due to their high quantum efficiency. To investigate the photoemission process in semiconductor thin-film photocathode under such conditions, we developed Monte-Carlo transport and photoemission models employing electronic, phonon, dielectric and optical properties directly from Density Functional Theory (DFT) calculation, as well as the photo excitation model based on the light interference effect in thin films. This photoemission model is further employed in photocathode gun simulation and used to investigate a recent high-gradient experiment conducted at the AWA photo injector. We will discuss the effects of the high field gradient on photoemission through a comparison of the measurement and the simulated beam dynamics.

*Work supported by the LDRD program at LANL.

Speaker: Chengkun Huang (Los Alamos National Lab)

26 Tunable photocathode double-bunch mode for advanced accelerator application

Generation and control of two electron bunches to achieve desired drive and witness quality is crucial for plasma-wakefield acceleration (PWFA) experiments. One scheme to generate two electron beams with desired spacing is to apply two laser pulses with ps delay on the photocathode and co-accelerated two electron beams in the same RF bucket. Such a method is used in e.g. two-color FEL[1,2,3] and PWFA experiments [4].This is also currently the standard running mode for PWFA experiment at FACET-II national user facility [5].

We will talk about the dynamic, operation, and control aspects of the photocathode two-bunches configuration with nC bunch charge, asymmetric bunch charge ratio, kA peak current, and multi-stage compression. We will talk about experimental performance, and benchmark it against simulation and analytic theory incorporating wakefield effect. We demonstrate excellent longitudinal simulation-experiment agreement using XTCAV measurements, and show that photocathode two bunches provide sufficient flexibility and tunability for various advanced accelerator applications.

[1] Marinelli, A., Ratner, D., Lutman, A. et al. High-intensity double-pulse X-ray free-electron laser. Nat Commun 6, 6369 (2015). https://doi.org/10.1038/ncomms7369

[2] Zhang, Z., Ding, Y., Marinelli, A. & Huang, Z. Longitudinal dynamics of twin electron bunches in the Linac Coherent Light Source. Phys. Rev. ST Accel. Beams 18, 030702 (2015). https://doi.org/10.1103/PhysRevSTAB.18.030702

[3] Chiadroni, E., Anania, M.P., Artioli, M. et al. Two Color FEL Driven by a Comb-like Electron Beam Distribution. Phys. Procedia 52, 27–35 (2014). https://doi.org/10.1016/j.phpro.2014.06.005

[4] Pompili, R., Anania, M.P., Bellaveglia, M. et al. Beam manipulation with velocity bunching for PWFA applications. Nucl. Instrum. Methods Phys. Res. A 829, 17–23 (2016). https://doi.org/10.1016/j.nima.2016.01.061

[5] Yakimenko, V., Alsberg, L., Bong, E. et al. FACET-II facility for advanced accelerator experimental tests. Phys. Rev. Accel. Beams 22, 101301 (2019). https://doi.org/10.1103/PhysRevAccelBeams.22.101301

Speaker: Yiheng Ye (SLAC/Stanford)

27 Towards Low-MTE Photocathodes in Accelerators

Most advanced electron beam applications, including particle colliders, X-ray free-electron lasers, and ultrafast electron diffraction and microscopy experiments, require beams with exceptionally high brightness. Electron sources must also exhibit long operational lifetime and robustness under the high electric fields and laser fluences characteristic of photoinjector environments. In the search for high-performance photoemissive electron sources, recent studies have identified epitaxially grown single-crystal cesium antimonides as highly promising candidates to provide low mean transverse energy (MTE) and high quantum efficiency (QE).

In this work, we present the experimental setup developed for the growth of alkali antimonide photocathodes by molecular beam epitaxy on lattice-matched substrates. Extensive testing and characterization of photocathodes will be carried out in the L-band RF gun of the Argonne Cathode Test-stand (ACT). To enable reliable transfer of photocathodes under ultra-high vacuum (UHV) conditions, a compatible cathode plug, load-lock system, and vacuum suitcase have been developed. RF and beam dynamics simulations of the newly designed plug have also been performed and will be discussed in this work.

Speaker: Oksana Chubenko (Northern Illinois University)

28 Cathode laser temporal shaping for LCLS-HE

The photon energy range of the LCLS-HE upgrade relies heavily on the achievable longitudinal beam brightness. The final peak current and correlated energy spread are both limited by the longitudinal phase space at the exit of the injector, non-linear compression, and collective effects. The initial charge distribution off the cathode effects all of these factors. However, determining an ideal cathode laser temporal profile requires optimization of the entire accelerator configuration. In order to simplify this problem, an idealized longitudinal phase space at the undulator entrance is analytically backtracked to the injector exit. In Astra simulations, the initial charge distribution and injector settings are optimized to match the longitudinal phase space from backtracking while maintaining a small projected emittance. The remainder of the accelerator is simulated in Elegant utilizing the lattice configuration determined by backtracking. The Free Electron Laser performance is simulated in Genesis using the start-to-end beam. Comparing with the nominal Gaussian cathode laser temporal profile, we find significant improvement in both the FEL pulse energy and maximum photon energy.

Speaker: Nicholas Sudar (SLAC)

29 Progress of the E31x program at SLAC FACET-II

The E31x program at SLAC FACET-II encompasses five distinct but complementary experiments: E-311 (Plasma Torch Injection), E-313 (Multibunch Dechirper), E-315 (Plasma Afterglow Attosecond Metrology), and E-316 (Icarus).These experiments represent a synergistic set of plasma wakefield acceleration (PWFA) experiments utilizing the unique combination of multi-kA electron bunches at 10 GeV and laser-ionized plasmas. Control over selective ionization of different gas species in PWFA crucially enables advanced ionization injection, acceleration, energy spread compensation, and diagnostics of ultra-high brightness electron beams. A recent upgrade to the probe laser system at FACET-II allowed the first experimental runs across this program. We present initial results from these runs, which will collectively establish a solid foundation for the forthcoming E-310 Trojan Horse-II experiments — the PWFA injection scheme with significant potential for producing high-quality, high-brightness electron beams.

Speaker: Edgar Anton Hartmann (Heinrich Heine University Düsseldorf)

15:30 Coffee break

A1-Working Group # 1

30 High-repetition-rate, all-reflective optical guiding and electron acceleration in helium using an off-axis axicon

We present recent results on high-power guiding and laser wakefield acceleration (LWFA) in the ELBA beamline at ELI Beamlines, driven by the L3-HAPLS laser system (13 J, 30 fs, 0.2 Hz). By employing self-waveguiding in a 20 cm helium plasma channel, we achieved stable acceleration of electron beams to energies of ~5 GeV. A novel all-reflective optical setup, incorporating an off-axis reflective axicon, enables efficient acceleration at 0.2 Hz and optical guiding at repetition rates up to 3.3 Hz. This compact, single-laser, single-compressor implementation of plasma channels improves electron beam pointing stability and enhances energy gain without requiring modifications to the laser system, paving the way for broader adoption of this approach at user facilities.

Speaker: Jiří Šišma (ELI Beamlines)

31 Revealing Laser and Electron Beam Evolution in 10-GeV-class Laser–Plasma Accelerators

Recently, channels formed by the hydrodynamic expansion of optical-field ionised plasmas (HOFI plasma channels) have received significant attention as suitable technology for efficient, high-energy laser-plasma accelerators (LPAs). In [1], we demonstrated high-quality PW-class laser guiding through 30-cm-long plasma channels, and controlled acceleration of singly peaked, quasimonoenergetic electron bunches to ~ 10 GeV. However, quantitative interpretation of such experiments is limited by substantial uncertainties in key plasma parameters, particularly the transverse density profile of HOFI plasma channels. Distinct plasma density distributions can produce similar terminal beam energies, complicating efforts to infer the underlying interaction physics from measurements at the accelerator exit alone. By combining longitudinally resolved electron beam diagnostics with independent measurements of laser spectral evolution in a 10 GeV LPA driven using the BELLA PW laser, we establish a multi-observable constraint on plasma density profiles [2]. The validated simulations indicate that extending the accelerator length to 65 cm would increase the electron beam energy to 15 GeV. They also point the way to achieving $\sim$ 20 GeV electron beams in $\sim$ 70 cm via linear matching using the same 24 J laser energy.

[1] A. Picksley et al., Phys. Rev. Lett (2024)
[2] H.Tang et al., https://arxiv.org/abs/2604.25823

This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and used the facilities at the National Energy Research Scientific Computing Center (NERSC) under award HEP-ERCAP0035612.

Speaker: Alex Picksley (Lawrence Berkeley National Laboratory)

32 Tunable, monoenergetic electron bunches with a π-step injector in optically guided laser wakefield acceleration

We present a new approach for producing monoenergetic, multi-GeV electron beams in an optically guided laser wakefield accelerator by utilizing a ‘π-step injector’. In this approach, spatiotemporal shaping of the channel-forming beam is employed to generate a short (≾drive beam Rayleigh range) null in the far field. This produces a localized modification of the channel structure which triggers injection within the accelerator. In proof-of-principle experiments with self-waveguided laser wakefield acceleration (SW-LWFA), this has enabled production of monoenergetic electron beams with tunable energies up to 3.5 GeV and charge up to tens of pC. Energy tuning may be achieved by varying the location of injection, accelerator length, or plasma conditions.

Speaker: Jaron Shrock (University of Maryland, College Park)

33 Dephasing Mitigation of Multi-GeV Electron Beams in a Ramped Plasma Waveguide

Laser wakefield acceleration (LWFA) in optically generated plasma waveguides has produced multi-GeV, high-charge electron beams. However, even in guided configurations, electron energy gain remains fundamentally limited by dephasing between the accelerated bunch and the plasma wake. In this talk, we present resent results demonstrating dephasing mitigation in self-waveguided LWFA through longitudinal tailoring of the plasma density profile. Using a modular gas jet, we generate customized tapered channels that rephase the electron bunch with the accelerating field, extending the effective acceleration length. Experiments performed in a ~20 cm plasma waveguide show up to a ~2x increase in electron energy compared to uniform-density channels under otherwise identical conditions, and peak energies reaching 4-6 GeV depending on the injection scheme. The effect is observed across multiple controlled injection methods, including localized ionization injection, pi-step injection, and laser-ablation of a copper target. These results are supported by theoretical scaling arguments and particle-in-cell simulations. The demonstrated control over longitudinal plasma structure provides a pathway toward higher-energy, high-efficiency LWFAs and scalable compact accelerators for secondary radiation and particle sources.

Speaker: Ela Rockafellow (University of Maryland)

34 Effects of laser-plasma waveguide coupling on accelerated electron bunch stability and spatial profiles

Self-waveguiding of petawatt-scale laser pulses in optical field ionized (OFI) plasma waveguides has opened a new era in multi-GeV laser wakefield acceleration (LWFA) of electrons. As these waveguides possess mode structure, details of coupling of the LWFA drive pulse into the waveguide are consequential to the acceleration process. This talk presents results from experiments at L-ALEPH in which the use of plasma waveguides with entrance funnels, generated with custom UMD diffractive optics, enhanced coupling to improve electron repeatability and charge with reduced sensitivity to laser misalignment and pointing fluctuations. Additional experiments show that the guiding of intense higher-order modes produces electron beams with corresponding spatial structure.

Speaker: Ari Sloss (University of Maryland, College Park)

35 Kilohertz Guiding and Laser Wakefield Acceleration in Optically Generated Plasma Channels

Optically generated plasma waveguides have recently enabled compact laser wakefield accelerators (LWFAs) producing multi-GeV, high-charge electron beams with sub-mrad divergence and pointing stability. However, nearly all demonstrations to date have operated at single-shot or Hz-scale repetition rates, leaving a gap between LWFA capabilities and the high average flux required by applications such as compact FEL drivers, radiobiology platforms, and other secondary radiation sources. Existing kilohertz LWFA sources typically rely on relativistic self-guiding, limiting the electron beam pointing stability and divergence, which are critical for many applications. In this talk, we present the first, to our knowledge, demonstration of guiding and LWFA in optically generated plasma waveguides at kilohertz repetition rate. The experimental platform utilized novel diffractive geometry and two synchronized OPCPA laser systems which provided an 8 mJ, ~15 fs channel-forming pulse and 0-400 ns delayed <40 mJ, 15 fs guided pulse. Low-power guiding was demonstrated in atmospheric-pressure air in ~1 cm channels while high-power guiding and LWFA was achieved over a 1-mm supersonic gas jet. Proof-of-principle experiments observed injection and acceleration of electron bunches reaching > 20 MeV with ~mrad divergence and pointing stability. These results establish kilohertz operation as a viable regime for guided LWFA and lay the groundwork for compact, high-average-power accelerators.

Speaker: Gabriel Brewster (University of Maryland)

A4-Working group # 4

36 Copper Coated Peek Based RF Cavity Power and Q Factor Testing

Lightweight, copper plated PEEK RF cavities offer a path to compact, low cost accelerators. We describe the design and fabrication of PEEK structures that are selectively metallized with high conductivity copper on RF surfaces, and outline a verification workflow used to qualify these cavities. Cavity quality factor (Q) is measured with a VNA using a critically coupled and a weakly coupled probe; from this the Q0 can be calculated and compared to a machined copper baseline. Power handling is evaluated under pulsed conditions, including RF conditioning, measurement of temperature rise and frequency drift. PEEK cavities that were doped with glass or carbon fibers were also tested to accommodate expansion of the copper plating by changing the thermal expansion rate of the PEEK to better match copper. Compared with solid copper, plated PEEK cavities reduce mass substantially due to the plastic substrate and enable rapid, geometry rich fabrication, but require careful thermal management and plating continuity to limit ohmic loss and detuning. Results indicate that, for moderate power levels, copper plated PEEK can approach copper like Q and stable operation while delivering significant weight savings.

Speaker: Benjamin Sims (LANL)

37 ASTERIX: Development of TIG-Welded Four-Quadrant X-Band RF Accelerating Structures at INFN.

The ASTERIX project, funded by the Istituto Nazionale di Fisica Nucleare (INFN) under the National Scientific Committee CSN5 program, focuses on the development of advanced X-band (11–12 GHz) accelerating structures based on hard copper and innovative manufacturing techniques. The project aims at the first demonstration of a practical, meter-long travelling-wave RF linac structure capable of operating at accelerating gradients exceeding 100 MV/m. The proposed design adopts an open-type geometry composed of four copper quadrants that are machined from solid blocks and joined using Tungsten Inert Gas (TIG) welding, enabling a braze-free, cost-effective, and robust fabrication process.

The RF design includes multi-cell travelling-wave cavities optimized for both single-bunch and multi-bunch operation. The four-quadrant configuration is intended to suppress dipole and quadrupole electromagnetic field components that can degrade beam dynamics. Integrated RF power couplers, two- and four-port geometries, are implemented to achieve compactness and mitigate unwanted field components. In addition, a secondary vacuum chamber is incorporated to improve pumping speed and to allow the installation of high-order-mode (HOM) absorbers when operating in multi-bunch regimes.

The research program includes RF design and wakefield/HOM characterization and optimization, fabrication of small-scale prototypes and a full-scale structure for single-bunch operation, and experimental validation through low-power RF measurements at the LATINO Laboratory and high-power RF testing at the TEX facility. Here, we present the project status and results from the first year, which include the production of the 1-m-long prototype to address the following main mechanical tasks: welding procedure, quadrant alignment and straightness, and vacuum tightness.

This effort is carried out within an international collaboration involving SLAC National Accelerator Laboratory, CERN, INFN Laboratori Nazionali di Frascati, KEK, and Tsinghua University, aimed at advancing high-gradient accelerator technologies crucial for the next generation of linear particle accelerators for research (such as linear colliders and light sources like EuPRAXIA@SPARC_LAB), as well as for industrial and medical applications.

Speaker: Luigi Faillace (Italian National Institute for Nuclear Physics (INFN))

38 Radiative damping in dielectric structures

For future implementation at UCLA's MITHRA linac, we present a study incorporating radiative damping in dielectric wakefield accelerator (DWA) structures. Of primary focus is manipulation of the HE11 hybrid mode, including mitigation of witness-beam break-up and production of orbital-angular momentum radiation. Design and use of a quadrupole array for strong focusing integrated into the DWA structure is also explored.

Speaker: Brian Naranjo (UCLA Dept. of Physics and Astronomy)

39 Towards Generation of Orbital Angular Momentum THz Radiation via Dielectric Wakefield Acceleration

Dielectric wakefield acceleration, driven by electron beams, generates high-power, narrowband terahertz radiation via the coherent Cherenkov emission. While conventional dielectric-lined waveguides have been studied extensively for fundamental mode excitation, recent theory suggests higher-order modes carrying orbital angular momentum (OAM) can be deliberately excited in modified structures. We present progress toward generation of OAM-carrying THz radiation using tailored drive beam distributions and novel dielectric geometries at the UCLA MITHRA accelerator facility. OAM modes introduce transverse field components with helical wavefronts, enabling simultaneous longitudinal acceleration and transverse focusing of witness beams. This integrated functionality may simplify beamline design and mitigate beam breakup instabilities that currently limit efficiency in wakefield accelerators. We discuss the theoretical framework, particle-in-cell simulation results, experimental configurations, and newly developed diagnostics for OAM mode characterization.

Speaker: JACKSON ROZELLS

40 Co-propagating dielectric laser accelerators for compact high-gradient particle acceleration

Dielectric Laser Accelerators (DLAs) are a promising approach for compact particle acceleration based on infrared lasers interacting with nanostructured dielectric materials. Operating at optical frequencies, these structures can sustain accelerating gradients well beyond the limits of conventional radio-frequency accelerators while enabling a drastic reduction of accelerator dimensions. Recent developments focus on extended dielectric waveguide structures supporting co-propagating electromagnetic modes synchronized with charged particle beams. This configuration enables longer interaction lengths and improved scalability compared with conventional transverse illumination schemes. This contribution presents recent advances in the design, modeling, and experimental investigation of dielectric interaction structures for particle acceleration in both sub-relativistic and relativistic regimes. Physics-based design methodologies and figures of merit for hollow-core dielectric waveguides are discussed, together with integrated beam dynamics simulations enabling co-design of electromagnetic structures and particle acceleration. This work is carried out within the European project EPITA (WP5: laser-driven acceleration) and within the INFN CSN5 iDLA project.

Speaker: Giuseppe Torrisi (Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS))

A5-Working group # 5

41 High temporal resolution THz streaking of high brightness relativistic electron beams

We present recent progress on a terahertz streaking diagnostic for ultrashort relativistic electron bunches at the UCLA Pegasus Laboratory. Single-cycle (~30 µJ) THz pulses centered at 0.5 THz are coupled into metallic structures, where field strengths are enhanced to several hundred MV/m and boundary conditions are tailored to produce a strong longitudinal streaking gradient. An initially long electron bunch emitted from the photocathode of an RF photoinjector is compressed in an S-band linac, generating femtosecond-scale current spikes within the longitudinal beam profile that are resolved using THz streaking. This approach enables single-shot measurements of MeV-scale electron bunches with femtosecond temporal resolution, with applications in advanced beam diagnostics and ultrafast science.

Speaker: Maximilian Lenz (University of California, Los Angeles)

42 High-Efficiency Attosecond-Resolution Terahertz Streaking of Relativistic Electron Beams

Terahertz (THz) streaking is a powerful technique for ultrafast longitudinal diagnosis of relativistic electron beams, as THz pulses generated via optical rectification are intrinsically synchronized to the driving laser and exhibit wavelengths well matched to the characteristic phase-space dimensions of relativistic electron bunches. However, the temporal resolution of THz streaking is often constrained to the femtosecond-level by the available THz pulse energy and the efficiency of the THz-electron interaction. Here we introduce a high-efficiency THz streaking scheme and the corresponding experiments conducted at the FORTRESS (Facility Of Relativistic Time-Resolved Electron Source and Scattering) beamline of Tsinghua University. Using single-cycle THz pulses with only a few microjoules of energy, the measurement precisions of 100 as level for bunch length and 10 as level for arrival time have been achieved. These results demonstrate the potential of THz streaking as a practical attosecond-level diagnosis tool for the next-generation ultrafast electron beam facilities.

Speaker: Mr Peng Lv (Tsinghua University)

43 THz-Driven Longitudinal Phase-Space Control and Diagnostics of Laser-Plasma-Accelerator Beams for Compact X-Ray Sources

Laser-plasma accelerators (LPAs) are highly promising drivers for compact X-ray free-electron lasers (XFELs). However, fully exploiting their ultrashort, high-current bunches requires mitigation of the percent-level energy chirp commonly present in LPA beams as well as diagnostics capable of resolving femtosecond temporal structure. Recent demonstrations using conventional radiofrequency (RF) cavities have successfully achieved active chirp correction of LPA beams, but the long RF wavelengths require millimeter-scale longitudinal bunch decompression to access sufficient field variation, reducing the peak current critical for FEL gain. Likewise, RF transverse deflecting structures can achieve excellent temporal resolution, but typically require large-scale infrastructure and sophisticated synchronization systems.

Terahertz (THz) fields provide a wavelength regime naturally matched to the native longitudinal scales of LPAs. For dechirping, a 1 THz driver ($\lambda \approx 300~\mu$m) requires only tens of micrometers of beam stretching to compensate correlated energy spread while largely preserving peak current, with estimated THz pulse energies in the ~1 mJ range. For diagnostics, THz streaking structures supporting GV/m fields can provide high-gradient transverse deflection with the potential for sub-10-fs temporal resolution. Because LPAs are intrinsically laser-driven, generating THz pulses directly from the LPA drive laser also provides optical synchronization to the electron beam, avoiding the timing complexity and residual jitter associated with external RF systems.

These applications are enabled by recent advances in high-energy THz generation and THz-driven accelerator technology. Laser-based nonlinear down-conversion techniques have recently enabled the generation of spectrally tailored mJ-class THz pulses suitable for accelerator applications. Concurrently, THz-driven accelerator structures have demonstrated high-gradient acceleration, compression, and streaking from the keV to multi-MeV regime, including recent operation at beam energies up to ~35 MeV.

This presentation will discuss recent work investigating the feasibility of applying THz-driven accelerator technology to direct manipulation of LPA beams. Initial calculations indicate that THz-driven dechirping and streaking are not only feasible, but offer substantial advantages for preserving ultrahigh peak current while enabling femtosecond-scale longitudinal diagnostics relevant to next-generation compact light sources. Recent progress in THz-source development and experimental validation of THz-driven accelerator structures will also be summarized to clarify the technological readiness of this approach.

Speaker: Nicholas Matlis (Arizona State University)

44 Compact THz Streaking Framework for Robust Longitudinal Diagnostics in Advanced Accelerators

We present a combined experimental and simulation study of terahertz (THz) streaking as a compact and flexible tool for longitudinal diagnostics in electron accelerator environments. By using image-domain comparison metrics and other optimal transport techniques applied to streaked and un-streaked beam profiles, we improve the robustness of longitudinal bunch measurements in realistic conditions, including nonlinear streaking fields, time-of-arrival jitter, and beam transport distortions. Using data collected at the Karlsruhe Institute of Technology (KIT) FLUTE accelerator to validate these observables, we explore optimized THz streaking geometries and beamline configurations through coupled electromagnetic and particle-tracking simulations, achieving improved signal-to-noise performance. The resulting framework provides a scalable diagnostic approach applicable to advanced accelerators spanning from compact beamlines at the university scale up to large emerging facilities like EuPRAXIA at ELI Beamlines where conventional RF-based diagnostics are impractical.

Speaker: Gerard Lawler (Paul Scherrer Institute)

45 Electro-Optic Sampling Beam Positioning Monitor for Relativistic Electron Beams

Non-destructive diagnostics able to resolve transverse offsets and longitudinal separation of ultra-relativistic, two-bunch electron beams are necessary for a variety of applications including the ion channel laser (ICL), a variety of plasma wakefield (PWFA) experiments, as well as other accelerator applications. We present an electro-optic sampling beam positioning monitor (EOS-BPM) design utilizing an ultra-fast laser pulse passing through an axicon lens to create a donut profile which images a multi-crystal structure placed around the axis of propagation of the electron beam to probe the individual transverse beam positions. We use the tilted pulse front produced by the axicon lens for an electro-optic spatial encoding scheme which allows for bunch separation measurements. This EOS-BPM design has been installed at the SLAC National Accelerator Laboratory FACET-II facility. This system is capable of order 5 fs temporal resolution and order 10 µm transverse position resolution and replaces the previously installed prototype design which was capable of order 10 fs and 100 µm transverse position resolution. Experimental results of the EOS-BPM in addition to the simulated response of this design to the ultra-relativistic, two-bunch electron beam used for PWFA experiments at FACET-II will be presented.

Speaker: Elena Ros (University of Colorado at Boulder)

46 Title: Phase-Diversity Electro-Optic Sampling for Shaped Electron Beam Profile Monitoring

Tailoring the longitudinal current profile for relativistic electron beams is essential for improving the efficiency of beam-driven wakefield acceleration. While various methods exist, applications involving ultra-high-energy or extreme current require non-invasive diagnostics. Electro-Optic Sampling (EOS) has the potential to provide non-invasive, single-shot access to the current profile with femtosecond resolution, which makes it a promising candidate for such environments. However, its application to the accurate measurement of shaped electron beams for wakefield accelerators remains limited. In this work, we investigate a Phase-Diversity Electro-Optic Sampling (DEOS) approach for measuring shaped bunches generated by an Emittance Exchange (EEX) beamline. Progress in the development will be presented.

Speaker: Spencer Kelham (Northern Illinois University)

A6-Working group # 6

47 Experimental Design and First Results from the Plasma-Driven Attosecond X-Ray Experiment at FACET-II

The ongoing Plasma-driven Attosecond X-ray source experiment (PAX) at FACET-II aims to produce coherent soft X-ray pulses of attosecond duration using a plasma wakefield accelerator [1]. These X-ray pulses can be used to study chemical processes where attosecond-scale electron motion is important. For this first stage of the experiment, PAX plans to demonstrate that <100 nm bunch length electron beams can be generated using the 10 GeV, 20 um duration beam accelerated in the FACET-II linac and using the plasma cell to give it a percent-per-micron chirp. The strongly chirped beam can then be compressed in a weak chicane to sub-100nm length, producing coherent synchrotron radiation in the final chicane magnet at wavelengths as low as 10s of nm. In this contribution we describe the results of recent experiments aiming to produce these ultra-compressed bunches and generate this single-cycle radiation, as well as the completion of the experimental setup of the PAX and early experimental measurements.
[1] C. Emma, X.Xu et al APL Photonics 6, 076107 (2021)

Speaker: Rafi Hessami (SLAC National Accelerator Laboratory)

48 Experimental demonstration of high-repetition-rate isolated attosecond pulses from a X-ray free-electron laser

The ultrafast motion of electrons drives chemical reactions and underpins material properties. Investigating these ultrafast dynamics demands state-of-the-art light sources, frequently requiring pulses with attosecond duration. The use of soft X-ray pulses makes it possible to probe electronic densities with atomic-site specificity. X-ray free-electron lasers (XFELs) have increased the per-pulse flux of attosecond sources by orders of magnitude, facilitating nonlinear and multidimensional spectroscopy in the X-ray regime. While multidimensional measurements provide higher fidelity of ultrafast dynamics, the significant statistical demands of these attosecond experiments have limited feasibility at low-repetition-rate sources. Here, we report the generation and temporal characterization of isolated attosecond X-ray pulses at a kilohertz repetition rate from a continuous-wave (CW) superconducting accelerator. This advance in repetition rate enabled a two-orders-of-magnitude reduction in data acquisition time for a representative attosecond pump-probe experiment, opening the door for mapping complex ultrafast dynamics with high dimensionality.

Speaker: Veronica Guo (Stanford University)

49 Ultracompact Strong-gain XFELs from High-field Plasma Wakefield Accelerators

Dephasingless high-field (>10-100 GV/m) plasma wakefield accelerators in the blowout regime can nowadays be experimentally realized in compact hybrid LWFA-PWFA accelerators [1]. These hybrids are ideal platforms for hosting plasma photocathodes [2], which require PWFA in the blowout regime for robust injection of ultralow (few tens of nm-rad) normalized emittance beams, and for emittance preservation at this level. We are in the process of developing these unique compact “high-field plasma photocathode PWFA” to produce electron beams with superior brightness, which then can robustly drive (X)-FELs at unprecedented gains. These “Strong-Gain XFELs” based on “High-Field PWFA” offer prospects for enhanced robustness and tunability, where brute-force lasing is enabled by the sheer brightness budget of the beams. At the same time, the Strong-Gain XFEL process can have highly desirable impact on photon-pulse quality and compactness, with saturation and therefore undulator lengths reduced to only a few meters.

These prospects make such systems potentially game-changing for the democratization and industrialization of XFEL technology. This contribution discusses the physics, as well as the scientific and industrial potential, of Strong-Gain XFELs driven by High-Field PWFAs at several operating points.

[1] Hidding et al., Phys. Rev. Letters 104, 195002 (2010)
[2] Kurz, Heinemann et al., Nat. Comm.12, 2895 (2021)
[3] Hidding et al., Phys. Rev. Letters 108, 035001 (2012)
[4] Deng, Karger et al., Nat. Phys. 15, 1156–1160 (2019)
[5] P. Ufer, A. Nutter et al., under review
[6] Habib et al., Nat. Comm. 14, 1054 (2023)
[7] Berman et al., https://arxiv.org/abs/2507.0640

Speaker: Bernhard Hidding (Heinrich Heine University Düsseldorf / University of Strathclyde / The Cockcroft Institute)

50 Over 8 hours of continuous operation of a free-electron laser driven by a laser-plasma accelerator

Since the emergence of laser-plasma accelerators (LPAs), substantial work has been dedicated towards using LPAs to drive free-electron lasers (FELs) for a broad range of applications. Despite recent breakthroughs, which have proven the fundamental feasibility of operating FELs with an LPA source, stable FEL operation over multiple hours without operator input had yet to be achieved. In this work, we report significant improvements to the stability of a hundred terawatt laser system, resulting in successful demonstration of reliable, long-term operation of an LPA-driven FEL in the self-amplified spontaneous emission (SASE) regime at 420 nm. The LPA source delivered 100 MeV electron beams at 1 Hz with high stability over more than ten hours, enabling over eight hours of continuous FEL operation without operator input. The acquired data was subsequently used to investigate correlations between the measured undulator radiation and parameters of the drive laser, plasma source, and electron beam. The revealed connections between LPA and FEL performance gave important additional insights into ways to further improve and stabilize the system, thus demonstrating the capability of our setup to serve as a powerful platform for future studies of LPA- driven FEL operation. The one-of-a-kind integration of multiple stabilization concepts onto the LPA facility discussed in this manuscript yielded significant accelerator and light source improvements (with residual correlations suggesting even more is possible), which will positively impact LPA applications at large.

Speaker: Finn Kohrell (Lawrence Berkeley National Laboratory)

51 Relativistic harmonics in the efficiency limit

Bright high-harmonic radiation from relativistically oscillating laser plasmas provides a direct route to generating extreme electromagnetic fields. Theory predicts that, under optimal conditions, the plasma can compress laser energy spatiotemporally into a Coherent Harmonic Focus (CHF), producing intensity boosts many orders of magnitude above the driving laser pulse. Diffraction-limited focusing and attosecond phase-locking have been demonstrated experimentally, but efficient coupling of relativistic laser energy into the harmonic emission cone has not previously been achieved.

Here we present that relativistic laser plasma interactions can be tuned to reach the high conversion efficiencies predicted by simulations. By enhancing the temporal profile of the driving pulse, we measure energies of 9 mJ between the 12th and 47th harmonics (18–73 eV). The measured efficiency scaling with harmonic order matches theoretical expectations, indicating near-optimal generation conditions. Achieving optimal efficiency together with full spatiotemporal compression remains challenging, these results open a path toward optical field strengths approaching the Schwinger limit $\mathbf{>10^{16}}$ V/m or $\mathbf{>10^{29}}$ W.cm$^{-2}$), enabling all-optical studies of the quantum vacuum and new frontiers in intense attosecond science.

Speaker: Jonathan Kennedy (Queen's University Belfast)

52 Relativistic Plasma Mirrors for Generating Bright Harmonics with Tuneable Polarization

A plasma mirror is formed when an intense laser pulse ionizes a solid target, creating an overdense plasma that reflects light specularly. In the relativistic regime($I \gtrsim 10^{18}Wcm^{-2}$ at $\lambda=800nm$), plasma mirrors generate high-order harmonics extending into the EUV and soft x-ray range. In the Coherent Synchrotron Emission (CSE) regime, relativistically driven electron nanobunches follow synchrotron-like trajectories and emit coherent, broadband radiation in attosecond bursts.
Control over the polarization of this emission is critical for applications such as magnetic circular dichroism and chiral spectroscopy. Here, we experimentally demonstrate tunable polarization of low-order harmonics by varying the polarization state of the driving laser($\lambda_0 = 800nm$, $\tau = 25fs$, $I = 10^{19}Wcm^{-2}$). Using Stokes polarimetry, we show continuous control from linear to circular polarization without significant loss of conversion efficiency.
Particle-in-cell simulations show strong agreement with experimental results for low-order harmonics and predict similar polarization trends at higher orders in the EUV. These results establish plasma mirrors as a promising route toward high-intensity, polarization-tunable EUV and attosecond sources.
This work was supported by the NSF Grants No. PHY 2206711, PHY 2512131, DOE Grant DE-SC0025497, and by the Gordon and Betty Moore Foundation, grant DOI 10.37807/GBMF12255.

Speaker: Vedin Dewan (Princeton University)

Poster Session Monday

Tuesday 28 July

Invited Talks: Plenary

53 Progress on Staging of LPAs

Laser–plasma accelerators (LPAs) sustain accelerating gradients orders of magnitude beyond those of radio frequency structures, offering compact sources of multi-GeV electron beams. Yet single-stage energy gain remains fundamentally constrained by laser depletion. Overcoming this limit requires staging: the sequential coupling of multiple plasma accelerator modules, each driven by an independent laser pulse.
In this talk, I will present recent progress toward practical LPA staging, focusing on three critical elements. The first is the production of a GeV-class first stage delivering percent-level energy spread with both shot-to-shot and day-to-day stability—performance that is essential for high-efficiency charge capture in a downstream stage. The second is compact refocusing of this beam using a capillary-discharge active plasma lens to enable efficient coupling into the subsequent accelerator module. The third element I will discuss is delivery of an independent drive laser to the second stage using a plasma mirror that enables compact integration along the electron beamline.
To assess operational robustness, I will present a tolerance study based on experimentally measured laser and electron-beam fluctuations. Misalignments, electron beam energy and energy spread variations, and timing jitter between the two drive pulses are investigated using particle-in-cell simulations. These studies quantify capture efficiency and staged energy gain under realistic operating conditions and define the stability requirements for future multi-stage systems.
Together, these advances represent concrete steps toward scalable, modular LPA architectures capable of extending electron energies beyond the limits of single-stage systems.

Speaker: Anthony Gonsalves (Lawrence Berkeley national laboratory)

54 Measurement of the Saturation Length and Reproducibility of the Self-Modulation Instability

The AWAKE experiment at CERN aims at driving plasma wakefields using a long, highly energetic (400GeV) proton bunch from the Super Proton Synchrotron, in principle enabling the acceleration of a witness bunch with a large gradient (>1GeV/m) over hundreds of meters. To drive these large amplitude wakefields, the long bunch must first be split into a train of microbunches through a transverse process, the self-modulation (SM) instability. High-gradient acceleration of a witness bunch can only occur after SM reaches saturation, making measurement of the saturation length crucial for the design of an SM-based accelerator.
We show that, by varying the plasma length and measuring the transverse profile of the bunch at a downstream screen, we directly observe for the first time the development of SM along the plasma. From these measurements, we determine the saturation length of SM, and study its dependence on key parameters, i.e., plasma density and initial wakefield amplitude.
In addition, and by using two independent diagnostics, we show that seeding makes the SM process reproducible from event to event, an essential requirement for producing a high-quality accelerated electron bunch.
We will introduce the AWAKE experiment, present these experimental results and their implications for long-term plans.

Speaker: Arthur Clairembaud (Max Planck Society (DE))

55 Experimental Demonstration of Beam-Driven Wakefield Acceleration in Laser-Plasma Filament

We have experimentally demonstrated plasma-based electron acceleration using laser-generated plasma filament as acceleration stage. In our experiments, we retrieve an energy gain of approximately 8 MeV (corresponding accelerating gradient 260 MV/m) in a 3-cm long plasma stage, together with a significantly enhanced stability of the acceleration process.
The work builds on a complete experimental and theoretical characterization of plasma filaments generated by low-energy (10 mJ), self-guided femtosecond laser pulses in low-pressure nitrogen, as published on Phys. Rev E [1]. Crucially, this approach allows us to propose plasma filaments as a tunable, high repetition-rate, low-energy dissipation plasma acceleration stage, with potential scalability of the interaction length to the meter scale. These features make filament-based stages particularly attractive for future light sources facilities based on plasma accelerators, as EuPRAXIA and EuPRAXIA-related systems.
We believe this work could be of broad interest because it introduces, for the first time, a beam-driven plasma acceleration stage based on the nonlinear self-guided propagation of an ultrashort laser pulse, rather than externally confined or preformed plasma structures. Beyond particle acceleration, this concept naturally connects to several topical areas, including nonlinear light–matter interaction, laser filamentation physics, compact accelerator technologies, and advanced plasma photonics. Moreover, the intrinsic tunability of the plasma stage length, together with high repetition-rate operation and low laser energy dissipation, makes this approach particularly well suited for the realization of plasma-based FEL user facilities, where stability, efficiency, and average flux are key requirements.
[1] M.Galletti et al, Femtosecond laser-induced plasma filaments for beam-driven plasma wakefield acceleration, Phys. Rev. E 111, 025202 (2025) DOI: https://doi.org/10.1103/PhysRevE.111.025202

Speaker: mario galletti (Laboratori Nazionali di Frascati - INFN)

10:15 Coffee Break

Invited Talks: Plenary

56 Recent progress on proton focusing using hemi-spherical targets at high repetition rate for proton fast ignition

Recent advances in high-intensity laser-driven proton focusing using hemispherical foils have enabled the generation of intense, localized proton beams. When thin foils are irradiated by ultraintense laser pulses (I > 10^19 W/cm²), broadband protons are produced via target-normal-sheath acceleration and subsequently focused by self-generated transient electric fields to 10–50 μm spots. In this talk, I will present recent experimental results demonstrating reproducible proton focusing at high repetition rate, along with scaling studies of focal properties with laser and target parameters. As one of the key applications, I will demonstrate isochoric heating of matter to warm dense matter conditions, reaching electron temperatures of tens of electronvolts using focused proton beams. These results highlight the potential of this approach as a practical platform for proton fast ignition research and other applications requiring precise delivery of energetic ions to dense matter.

Speaker: Sophia Malko (Princeton Plasma Physics Laboratory)

57 GeV-Scale Ion Acceleration in Underdense Plasma with a Transverse Flying-Focus Laser Pulse

High-intensity laser-plasma interactions provide access to accelerating fields far exceeding those achievable in conventional accelerators, offering a pathway toward compact sources of energetic particles. However, accelerated ion energies in laser-driven experiments are currently limited to approximately 150 MeV per nucleon; the small charge-to-mass ratio of ions makes standard laser wakefield acceleration inefficient. In this work, we show that a relativistic laser pulse with a focal spot sweeping transversely across the propagation axis—a transverse flying-focus configuration—can enable efficient wakefield acceleration of ions in underdense plasma. Three-dimensional particle-in-cell simulations demonstrate that this spatiotemporally structured pulse generates a co-moving electrostatic trapping region capable of capturing and accelerating ions to GeV energies. For a peak laser intensity of $10^{20}$ W/cm2 and an acceleration length of 0.44 cm, the mechanism produces a proton beam with 23.1 pC charge, a peak energy of 1.6 GeV, and a relative energy spread of 3.7%. These results indicate that a transverse flying-focus configuration provides a promising route toward compact, high-repetition-rate sources of high-energy ions and illustrate the broader potential of advanced spatiotemporal pulse shaping for overcoming long-standing limitations in laser-plasma accelerators.

Speaker: Sida Cao (Stanford University)

58 Simulation methods for the plasma injector for Petra IV

Petra IV, the upcoming fourth-generation synchrotron light source at DESY, ambitions to become the world’s brightest X-ray source. Installed in the PETRA tunnel, it consists of a 2.3-km circumference ring storing 1,920 bunches at 6 GeV, for a total charge of 1,500 nC. In 2024, we published a Conceptual Design Report [A. Martinez de la Ossa et al., DESY, 2024 https://doi.org/10.3204/PUBDB-2024-06078] documenting a plasma-based alternative to the baseline injection system (450 MeV linac + booster). The tight requirements of a 6-GeV laser-plasma accelerator (LPA) delivering 4 nC/s within 1% energy acceptance were met thanks to an energy compression beamline to control the energy spread and jitter. In this talk, we present the suite of simulations tools used to perform this study as well as methods for start-to-end pipelines combining electromagnetic particle-in-cell (PIC), quasistatic PIC, beam dynamics and Bayesian optimization. Recent progress to simulate the formation of the hydrodynamic optical-field-ionized (HOFI) channel to guide the high-energy LPA will be discussed, as well as considerations on transverse jitters and tolerances. The open-source toolkit for start-to-end simulations from plasma source formation to application can be used for a wide range of problems pertaining to beam-driven and laser-driven plasma acceleration.

Speaker: Maxence Thevenet

12:15 Lunch

A1-Working Group # 1

59 EuPRAXIA@ELI: Hybrid plasma accelerator approach to XFEL

The EuPRAXIA project on the European Strategy Forum on Research Infrastructure roadmap aims for “superior beam quality”, with plasma-based (X)FEL as flagship application. Such superior beam quality and XFELs can be achieved by a combination hybrid plasma wakefield accelerators and the Trojan Horse approach, key components of the “Transformative Innovation Paths” Work Package of EuPRAXIA and the “NeXource: Next-generation Plasma-based Electron Beam Sources for High-brightness Photon Science” ERC project.
This contribution discusses integrated advanced accelerator and XFEL concepts for the foreseen Phase-I (water window) and Phase-II (hard XFEL) capabilities at the Extreme Light Infrastructure, which was recently selected as the LWFA pillar of EuPRAXIA. These concepts can provide the superior electron and XFEL pulse quality required to secure the competitive edge of the EuPRAXIA infrastructure.

Speaker: Bernhard Hidding (Heinrich Heine University Düsseldorf / University of Strathclyde / The Cockcroft Institute)

60 Effects of Controlled Laser Wavefront Aberrations on Charge Trapping, Electron Beams, and Betatron X-rays in Petawatt Laser Wakefield Acceleration

Laser wakefield acceleration is strongly influenced by the spatial and spatiotemporal structure of the drive laser pulse, yet the role of controlled wavefront aberrations at petawatt power remains largely unexplored. In this work, we investigate the effect of manually induced laser wavefront aberrations on GeV-scale electron beams and betatron X-ray emission produced at the ZEUS facility. Using a 12-inch deformable mirror, we systematically applied 45-degree astigmatism, horizontal coma, and 0-degree trefoil to a 1.12 PW, f/61 laser pulse driving ionization-injection wakefield acceleration in a 6 cm gas cell at a plasma density of approximately 5×$10^{17}$ cm$^{−3}$. Controlled aberrations were found to significantly modify both electron and X-ray beam properties. Astigmatism increased the ellipticity and divergence of the betatron X-ray profile, while all tested aberrations generally reduced the X-ray flux. Reconstructed betatron spectra suggest that astigmatism and trefoil soften the X-ray spectrum, whereas moderate horizontal coma may increase the inferred critical energy. Electron spectra showed reduced maximum energy at larger coma and trefoil strengths, while astigmatism had a weaker effect on peak energy. Measurements from a newly commissioned electron beam profiler revealed that increasing astigmatism can increase the fraction of charge contained in the central beam relative to the surrounding halo. This trapping-efficiency trend was qualitatively reproduced in reduced-scale FBPIC simulations using an astigmatic laser driver. Overall, these results demonstrate that controlled wavefront aberrations provide a useful handle for modifying injection, electron beam structure, and betatron X-ray emission in petawatt-class laser wakefield accelerators.

Speaker: Tanner Nutting (Univerisity of Michigan)

61 Controlled Electron Injection in LWFA using a Segmented Capillary Gas-Cell

A segmented capillary gas cell was developed to enable precise control over electron injection and acceleration in laser wakefield acceleration (LWFA). This system is composed of multiple capillary segments, each with specially designed apertures and independently supplied with gas, allowing the formation of tailored longitudinal density gradients. At the center, a narrower orifice creates a pressure down-gradient, leading to plasma density modulation when ionized. The intended density structure was validated through Stark broadening of hydrogen emission spectra generated by the discharge in the gas cell. In LWFA experiments using a 150 TW laser, this design produced electron beams reaching 300 MeV, showing reduced energy spread and enhanced shot-to-shot stability compared to traditional uniform capillaries. This segmented configuration offers a promising method for improving plasma-based acceleration by enabling fine control of plasma density profiles.

Speaker: Inhyuk Nam (Ulsan National Institute of Science and Technology (UNIST))

62 Self-loading LWFA using two-color ionization injection with flying-focus lasers

The plasma accelerator community has made impressive strides in developing methods to optimize beam injection schemes needed to make laser wakefield accelerators (LWFAs) viable for collider applications. One such technique is two-color flying-focus ionization injection, where a drive laser partially ionizes a gas and excites a nonlinear wake, and an injector laser with a much shorter wavelength focuses inside the wake. The injector further ionizes the gas and generates an electron beam that can be trapped and accelerated. The flying-focus technique allows us to control the spatiotemporal profile of the injector in order to maintain a near-constant intensity peak which propagates at a programmable velocity. Controlling the injector's properties in this way allows us to generate a beam with a trapezoidal linear charge density, which flattens the wake's electric field and results in very low energy spread. This method was previously investigated in simulations with a 20 TW, 9.2 $\mu$m CO$_2$ drive laser and a 400 nm Ti:Sapphire (second harmonic) injector, achieving $\sim$200 pC of injected charge with an energy spread below 1\% and $\sim$100 nm$\cdot$rad normalized emittances (https://doi.org/10.1103/q36y-6jqn). In this study, we explore the viability of this technique using a more typical PW-class near-IR laser. We perform quasi-3D particle-in-cell simulations with experimentally-relevant parameters for testing this method at Lawrence Berkeley National Laboratory (LBNL). We use an 800 nm Ti:Sapphire laser to drive the wake and a 267 nm (third harmonic) flying-focus laser as the injector, with the parameters of both LBNL's 100-TW and 1-PW systems considered. We will show preliminary simulation results and discuss the challenges with designing an experiment to demonstrate injection and acceleration of a high quality beam with this configuration.
This material is based upon work supported by the National Science Foundation under Grant No. PHY-2238840. This material is also based on resources of the NERSC facility, operated under Contract No. DE-AC02-5CH11231

Speaker: Evan Trommer (Stony Brook University)

63 High Quality Electron Beams for Staging at BELLA PW

Staging of Laser Plasma Accelerators (LPAs) towards high charge, high energy electron beams requires a stable first stage providing low energy spread beams for subsequent transport and acceleration. To ensure high capture efficiency in the second stage, the electron beam is imaged by an active plasma lens. High capture efficiency requires the beam’s energy spread to remain sufficiently low (<5%) to reduce chromatic focusing effects during transport which lead to an increase in spot size at the second stage. This talk will cover the status of the first stage of the staged accelerator at the BELLA PW facility. This includes reliable day to day performance of low-energy spread GeV beams, dependence of beam parameters with laser fluctuations, and status of laser stabilization systems.

Work supported by the United States Department of Energy Office of Science, Offices of HEP under Contract No. DE-AC02-05CH11231.

Speaker: Aodhan McIlvenny (Lawrence Berkeley National Lab)

64 Path to High-Quality, High-Charge LWFA Beams for Light-source and Collider Applications

To build a compact injector for free-electron lasers, colliders or storage rings, we require beam metrics that are difficult to realize together in laser wakefield accelerators. Experiments have demonstrated high charge and emittance control independently, but none so far has demonstrated sub-percent energy spread at high charge or efficiency. Although gas jets and shock injection have provided very low energy spread in the past, they are disfavored by high repetition rate operation. For this reason, we compare engineering the current profile using density ramp steepness and contrast at injection, and controlling emittance and longitudinal phase space at the exit ramp. Our goal is to sketch laser, plasma and accelerator design requirements and tensions in delivering high bunch charge (100s of pC), sub-percent energy spread, and normalized transverse emittance below 0.1 mm mrad.

Speaker: Lance Labun (University of Texas, Austin)

A3-Working group # 3

65 Teraelectronvolt plasma acceleration through regenerative cascading

High accelerating gradients make plasma wakefield accelerators an attractive candidate for future teraelectronvolt (TeV) machines, but conventional staging concepts accelerate a single witness bunch through many independent stages, and maintaining its quality across every interface imposes stringent tolerances on alignment, timing, and matching. In this talk, we propose an alternative architecture—plasma acceleration through regenerative cascading (PARC)—in which the witness accelerated in one stage serves as the driver for the next, while a new witness is freshly self-injected within each stage. Two consequences follow: stage energy gains compound multiplicatively instead of additively, and the staging tolerances are eliminated because each self-injected witness is automatically aligned, synchronized, and potentially matched to the wake. Start-to-end particle-in-cell simulations show that a 45 GeV, 100 nC driver yields a ~1.1 TeV, 0.12 nC beam with 0.3% rms energy spread and 4 mm-mrad normalized emittance in just two stages totaling less than a kilometer of plasma. PARC shifts the difficulty of TeV plasma acceleration away from staging and onto driver generation, where several viable technologies are already under development.

Acknowledgements. This work was supported by the U.S. Department of Energy under Grant No. DE-SC0010064, as well as by the University of California, Los Angeles. Simulations used resources of NERSC under Contract No. DE-AC02-05CH11231 (Award HEP-ERCAP-MP113).

Speaker: Chaojie Zhang (University of California Los Angeles)

66 Nonlinear Theory for Plasma Wakefield Produced by Elliptical Beams via Data-Driven Physical Modeling

Plasma-based acceleration is widely regarded as a highly promising candidate technology for next-generation linear colliders and light sources. In the blowout regime of plasma wakefield acceleration, an intense particle beam excites a nonlinear plasma wake. However, there is currently no theory that can fully predict the asymmetric nonlinear wakefields generated by elliptical beam drivers. Machine learning provides an alternative approach for predicting physical quantities from simulation data with improved accuracy and efficiency. In particular, physics-informed methods incorporate known physical laws into the learning process, enabling accurate and interpretable surrogate models for complex systems. In this work, we focus on developing a nonlinear theory for plasma wakefield produced by elliptical electron beams via data-driven physical modeling. We employ physics-informed machine learning to approximate components of the blowout theory that are analytically difficult to describe, enabling the discovery of governing equations for the wakefields. Preliminary results show good agreement with simulations in both the blowout radius and wakefields.

Speaker: Tony Griffin (Old Dominon University)

67 High-energy plasma wakefield acceleration with full charge capture in a laser-ionized all-optical plasma source

Beam-driven plasma wakefield acceleration is a leading candidate for a future electron–positron collider, but it requires transferring a large amount of energy and precise control of the plasma profile. Laser-ionized plasma sources offer significant advantages in meeting these demands. In this work, we present a detailed characterization and simulation of a laser-ionized, all-optical plasma source. We demonstrate—for the first time—high energy transfer with high total efficiency in a beam-loaded PWFA, along with up to 100% witness charge capture in an all-optical plasma soruce, in good agreement with simulations. We also show how this approach can be extended toward positron acceleration. These results establish laser-ionized plasmas as a controllable and high-performance platform for PWFA, and mark an important step toward collider-relevant operation.

Speaker: Valentina Lee (University of Colorado Boulder)

68 PROGRESS ON THE FLAT BEAM PLASMA WAKEFIELD EXPERIMENT AT AWA

The flat beam plasma wakefield acceleration experiment at the Argonne Wakefield Accelerator investigates asymmetric beam-driven plasma wake excitation using transversely shaped electron beams having a large transverse aspect ratio to study novel wakefield structures and beam–plasma interactions relevant to advanced accelerator concepts. Magnetized beams at the cathode were transformed into flat beams using skew quadrupoles for emittance partitioning. In parallel, the plasma source has been tested and commissioned at AWA, and is currently being integrated with the beamline for upcoming experimental studies. Initial beam–plasma interaction measurements are expected in the near term, with preliminary results anticipated by the time of the conference. This work contributes to understanding elliptical wake excitation from flat beam geometries.

Speaker: Pratik Manwani (University of California, Los Angeles)

69 Optimization of plasma-based electron injectors for a linear collider or XFEL

Plasma-based accelerators have attracted significant interest in XFEL and linear collider applications due to the high quality, multi-GeV electron beams they can produce. Through particle-in-cell simulations, we demonstrate a plasma-based injector concept to generate 80+ GeV electron beams with nC-level charge, sub-percent energy spreads and high brightness > 10^19 A/m^2/rad^2. This concept relies on self-focusing of an electron driver beam to facilitate wake expansion and self-injection in the plasma. However, the same ideas can be applied to self-injection from other expanding bubble concepts such as density downramp injection. The results improve upon previous work [1] by shaping the drive bunch and scaling its charge and energy for high transformer ratio acceleration (R > 2). Electron beams produced using this approach may be suitable for use in the electron arm of a future linear collider or Higgs Factory.

This work was supported by US DOE grants No. DE-SC0010064 and DE-SC0025612.

[1] T. N. Dalichaouch, et al., PRR. 7, 023118 (2025).

Speaker: Thamine Dalichaouch (UCLA)

70 Performance enhancement of electron beams from linacs, LWFA or PWFA

The prospects of PWFA for boosting electron energies via high transformer ratios, as well as the prospects for ultralow-emittance beam production using plasma photocathodes [1], are widely discussed. Contrary to the traditional experience of accelerator scientists, we anticipate that the production of ultrabright beams exceeding the current state of the art by orders of magnitude via these mechanisms is not associated with increased challenges regarding tolerances and jitter. Instead, such beams may enable the opposite: relaxed demands on the quality, precision, reproducibility and stability of incoming beams [2].
This counterintuitive feature – with potentially extremely high impact for feasibility of plasma photocathodes and their applications – will be discussed in this contribution. An example is insensitivity towards timing jitter: contrary to concerns, timing fluctuations of several tens of femtoseconds of the plasma photocathode laser with respect to the plasma wave do not lead to large variations of the produced electron witness beam, but instead to virtually identical witness beams and corresponding simulated FEL performance, which we show in extension of [3].

[1] Habib, Heinemann et al., Plasma Photocathodes, Annalen der Physik, September 2023 https://doi.org/10.1002/andp.202200655
[2] Campbell et al.,Phys. Rev. Research 8, 013273 (2026)
[3] Berman et al., https://arxiv.org/abs/2507.0640

Speaker: Bernhard Hidding (Heinrich Heine University Düsseldorf / University of Strathclyde / The Cockcroft Institute)

A5-Working group # 5

71 Cavity-Based Beam Charge and Arrival Time Monitor

Non-destructive bunch characterization is essential across a wide range of accelerator applications. Precise measurement of bunch charge is critical for correlating sample response with delivered dose, while femtosecond-level time-of-arrival (TOA) precision is paramount for resolving transient structural dynamics in pump-probe experiments. Cavity-based beam monitors, which exploit wake field excitation by the beam, offer highly sensitive single-shot access to both observables. Recent experiments at UCLA PEGASUS have demonstrated sub-fC charge sensitivity with ongoing work to understand the theoretical and practical limits of both charge and TOA measurements. To extend these capabilities toward real-time operation, the Beam Arrival Monitor (BAM) cavity is being integrated with an RFSoC-based digital LLRF platform, combining an FPGA, multi-core ARM processor, and high-speed ADCs and DACs on a single chip. This architecture enables multichannel processing, low-latency deterministic feedback, and a pathway to deploying physics-informed machine learning models for noise suppression and drift correction, laying the groundwork for robust sub-10 fs synchronization and high accuracy charge characterization in next-generation experiments.

Speaker: Atharva Kulkarni (UCLA Particle Beam Physics Lab)

72 The role of coherent Smith-Purcell radiation for LWFA e-beam diagnosis

Laser Wakefield Acceleration (LWFA) is a highly promising, compact acceleration scheme capable of generating energetic, ultra-short, femtosecond-scale electron bunches (e-bunches). However, the extreme spatial and temporal scales inherent to LWFA e-bunches make their non-destructive, single-shot characterization exceptionally challenging. This presentation provides a comprehensive overview of utilizing coherent Smith-Purcell radiation (CSPR) as a robust, non-intercepting diagnostic pathway to address this challenge. When a charged particle bunch passes in close proximity to a periodic conductive structure, it excites surface currents that emit CSPR. Because the spectral intensity distribution of this radiation is directly linked to the bunch's longitudinal form factor, it allows for accurate bunch profile reconstruction. We will detail the theoretical underpinnings of CSPR generation within the context of LWFA e-bunch parameters and discuss practical methodologies to extract e-bunch structure from measured CSPR spectra.

Speaker: Mr Ross Rudzinsky (The University of Texas at Austin)

73 All-optical, quasi-real-time measurement of the 3- and higher-dimensional structure of microbunched electrons from a laser-driven wakefield accelerator

Electrons microbunch in laser wakefield accelerators [1,2], in downstream light sources [3], and in laser modulators [4]. Precisely measuring the 3D microbunched density of the electron bunches is vital for understanding wakefield dynamics and optimizing electron-driven radiation processes. Multi-spectral coherent transition radiation (CTR) imaging measurements [5] have decoded such 3D microbunched structure, but requires independent simulation or non-optical measurement of the bunch longitudinal profile. Moreover, it took hours for the genetic reconstruction algorithm to converge, prohibiting real-time feedback and adjustment of a wakefield accelerator or free electron laser (FEL). Here, we present results of new experiments in which the spatially-averaged CTR spectrum and CTR images at eleven wavelengths were measured simultaneously, yielding in one shot all the information needed to retrieve the 3D microbunched structure. We then employed a pre-trained physics-informed neural network to reconstruct the electron density profile within one minute with better fidelity than previously [5]. Finally, by extending the measurements to interferometric CTR, with two CTR foils [6] in the diagnostic beam line, we enable single-shot, all-optical, minimal-invasive 5D visualization of the electron bunches.

Ref:
[1] Xu et al, Phys. Rev. Lett 117, 034801 (2016)
[2] Xu et al, Nat. Commun. 13:3364 (2022)
[3] Wang et al, Nature 595, 516-520 (2021)
[4] Deng et al, Nature 590, 576-579 (2021)
[5] LaBerge et al, Nat. Photon. 18 952-959 (2024)
[6] Lumpkin et al, PRL 125, 014801 (2020)

Speaker: Ze Ouyang (The University of Texas at Austin)

74 Revealing critical electron beam parameters with advanced coherent transition radiation techniques

Plasma accelerators have delivered beams of sufficient quality to drive free electron lasers (FELs). However, greater resolution and, ultimately, control of the electron beam's six-dimensional phase space is needed to drive FELs consistently with sufficient gain at sub-micrometer wavelengths, as well as to address future challenges for laser wakefield accelerators (LWFAs), such as staging. In particle-in-cell simulations, injection methods such as self-truncated ionization, tailored down-ramps and plasma photocathodes have shown promise for producing high brightness beams. However, single-shot measurement of the critical parameters that are needed to quantify the correlated phase space remains elusive. Here we present recent experimental results taken at the DRACO laser system at HZDR using compact, single shot, coherent-transition-radiation diagnostics coupled with machine learning techniques to elucidate critical electron beam parameters. Employing both a spectrometer as well as a multi-spectral imaging system, we observe spectral-spatially encoded electron beam information, which, with in-house developed machine learning techniques, we are able to extract critical electron beam phase space information. We use this diagnostic feedback for our optimization of down-ramp and ionization injection LWFA regimes. Finally, we also comment on multi-beam features observed when using the LWFA electron beam to drive a wakefield in a second stage.

Speaker: Maxwell LaBerge

75 Characterizing a Gas-Ionization Platform for Single-Shot Beam Diagnostics

Minimally-invasive single-shot beam diagnostics are essential for the next generation of high-brightness electron accelerators. We report on the ongoing development of an ionization-based beam profile monitor utilizing a supersonic nitrogen gas sheet target. Recent progress has focused extensively on characterizing the precise density profile of the gas target, which is critical for accurate beam profiling. By systematically sweeping an ionizing laser across the gas sheet and imaging the subsequent recombination luminescence, we have successfully resolved spatial maps of the gas density. These empirical density maps provide vital feedback on current gas jet dynamics and are actively informing the design and optimization of nozzle geometries.

In parallel with experimental nozzle characterization, we are advancing the diagnostic's electrostatic optic column using General Particle Tracer (GPT) simulations. This computational work optimizes the electrostatic column geometry and focusing profiles for both high-resolution spatial imaging and Velocity Map Imaging (VMI). Furthermore, we are modeling the "streaking" dynamics of ions born within intense fields, such as the ionizing laser pulse or the space-charge field of a driving electron beam, utilizing simulation parameters specifically matched to the operational capabilities of the PEGASUS beamline at UCLA. By simulating this momentum kick within a VMI configuration, we are establishing a framework to resolve the time of ionization of the individual gas molecules. This presentation will detail our experimental gas mapping techniques and outline the simulation framework in preparation for experiments at the PEGASUS facility.

Speaker: Travis Nichols (UCLA)

76 Design of a Compact Photoconductive Antenna for Direct Femtosecond-Micron Measurement of 3D Space-Charge Fields

Accurate characterization of 3D space-charge fields in ultrashort electron beams is crucial for next-generation accelerators. The complex, transient 3D space-charge and CSR fields that ultimately shape and limit high-brightness beams have yet to be directly measured, leaving critical dynamics unobserved. A compact diagnostic for the direct measurement of the field itself thus remains a key challenge.
We present a compact Photoconductive Antenna (PCA) diagnostic for direct field measurement at the LCLS. The PCA operates by using a soft X-ray (SXR) pulse, collimated by a laser-drilled aperture, to generate localized free charge carriers in a diamond sensor. The transverse space-charge field of a passing electron bunch then drives these carriers, inducing a measurable current in a nearby antenna via the Ramo-Shockley theorem.
A full 3D spatiotemporal field map is reconstructed by mechanically scanning the device for transverse (x-y) resolution and varying the X-ray arrival time using an SXR delay line for femtosecond-scale longitudinal (z) resolution. This presentation will cover the PCA's operational principle and design for LCLS. By providing a direct, femtosecond-micron measurement of the beam's vector field, rather than its scalar charge density, the PCA offers a unique capability for optimizing beam performance in advanced accelerators.

Speaker: Sean OTool (Stanford)

A6-Working group # 6

77 Applications of a Compact Positron Source as a Source of Entangled Gamma Rays

We present a compact, ultrafast positron source design for SLAC National Accelerator Laboratory which will provide up to 100,000 e+/s at 30 Hz, with tunable energies from 1 to 5 MeV. A primary near-term application is precision-timed entangled gamma ray pair generation for next-generation PET (Positron Emission Tomography) detector development and calibration. Conventional PET detector testing relies on radioactive sources that cannot provide control over timing or event rates. By using a linac source, we will generate positron beams that, upon annihilation on a thin tungsten target, produce entangled 511 keV gamma ray pairs with precisely defined temporal structure. Beyond medical applications, we explain how this positron source enables time-gated ghost imaging of dense materials, leveraging entangled photon correlations for low signal to noise. Finally, we will discuss longer term positron applications in semiconductor development and basic material studies, highlighting the versatility of a compact positron source.

Speaker: Sophie Crisp (scrisp11@slac.stanford.edu)

78 A laser-based high average yield neutron source for medical applications

Generation of neutrons with lasers has been in the focus of research and development for over two decades. Such neutron sources exhibit unique properties as inherently pulsed operation, ultrashort pulse duration (around and below nanosecond), and small source size. Besides, the driving laser is not a nuclear device, and there are no proliferation issues. Hence, it is an inherently safe pulsed neutron source which capable to produce high flux rate neutrons to a target under examination in a cost effective way.
A laser-based neutron source was developed by the National Laser-Initiated Transmutation Laboratory of the University of Szeged, and commissioned in the Hungarian site of ELI ERIC. Laser pulses from the 1 kHz repetition rate SYLOS3 laser were focused onto an ultrathin heavy water sheet in vacuum. The 80 mJ, sub-10 fs laser pulses accelerated deuterons to a cut-off energy around 2 MeV, which induced a $^2H(d,n)^3H$ fusion reaction in a heavy water flowing sheet as a neutron catcher. The resulting neutrons have a directionality along the propagating direction of the deuteron ions, and a unique feature of quasi-monoenergetic spectrum centered around 3.2 MeV. We maximized the neutron yield per laser shot by tuning the dispersion, and hence the temporal shape of the laser pulse. The average neutron flux was $10^8$ $neutron/ cm^2/s$ on the target, while the peak neutron flux rate of a neutron pulse was estimated close to $10^{13} neutron/cm^2/s$. The system was demonstrated working with a continuous, stable operation (<5% rms) for over 4 hours.
First, a total of 1.6 Gy dose was delivered on zebrafish embryos. The density of apoptotic cells as well as double-strand breaks in the zebrafish embryos was similar to that of the control group irradiated with cyclotron-generated neutrons. However, photomotor responses showed differences.
In a second experiment we explored the viability of laser driven neutron sources to produce theranostics radiopharmaceuticals for imaging and cancer treatment. At present, the demand for the radiopharmaceuticals Lu-177, Tb-161, Cu-67, and Cu-64 is hitting global production limits and a solution needs to be found to increase supply. In this first pilot experiments, we were able to prove the production of Cu-64 with extra high purity. Further analysis of the quality and outcome of these trials is underway.

Speaker: Prof. Karoly Osvay (Extreme Light Infrastructure ERIC)

79 A platform for radiobiology research using very-high energy (VHEE) laser plasma accelerated electrons at BELLA

External beam radiotherapy remains the standard of care for more than half of all cancer patients worldwide. In recent years, the use of very high energy electrons (VHEE) in the 50–250 MeV range has attracted considerable interest for radiotherapeutic applications, particularly in the treatment of deep-seated tumors. VHEE beams generated via laser-plasma acceleration (LPA) are characterized by ultra-short electron bunches and extremely high instantaneous dose rates, holding promise for their use in investigating ultra-high dose rate phenomena such as the FLASH effect. This compelling modality has demonstrated significant reductions in normal tissue toxicity and inflammation during external beam radiotherapy.
To advance research in this area, we have established a dedicated experimental platform at BELLA to study the biological effectiveness of VHEE produced by compact LPA technology. Robust beam delivery and dosimetry protocols have been developed to support the irradiation of biological samples within a purpose-built sample irradiation area. A set of normal and tumor cell lines, as well as a range of peptide samples, were irradiated using LPA VHEE bunches characterized by broad electron energy spectra spanning 50–200 MeV and a bunch charge of approximately 200 pC. Between 50 and 400 LPA bunches were accumulated to deliver total doses ranging from 5 to 20 Gy to the biological samples. Radiation damage was assessed through clonogenic survival assays and peptide oxidation analyses. These results were subsequently benchmarked against X-ray exposures conducted at the Advanced Light Source, utilizing ultra-high dose rate soft X-rays, as well as conventional dose rate irradiations performed with a 300 kVp X-ray tube.
This presentation introduces the newly established BELLA VHEE platform and highlights preliminary findings from the biological sample irradiation campaign.

Funding acknowledgement: This work was supported by the Lawrence Berkeley National Laboratory Laboratory Directed Research and Development (LDRD) funding provided by the Director.

Speaker: Lieselotte Obst-Huebl (Lawrence Berkeley National Laboratory)

80 Medical Applications of Ultrasound from Plasma-Accelerated Electrons

Radiation-induced Acoustic Computed Tomography is an imaging modality that combines the high penetrability of ionizing radiation with the flexibility of detection of ultrasounds. A single short pulse of electrons or x-rays locally heats an absorber inside the object of study, launching ultrasound waves in three dimensions that transducers outside the object detect. This enables image reconstruction and other analyses in one shot, thereby minimizing exposure to ionizing radiation. Efficient generation of acoustic waves in most materials require that the energy deposition happens in some nanoseconds. Only a few commercial x-ray generators operate at these durations, and they are limited in their energy output. Laser Wakefield Accelerators (LWFA’s), on the other hand produce femtosecond bunches and are energy-tunable, making them an attractive option for this application.
Here, we irradiate various targets with single ~100 MeV electron bunches from a laser-wakefield accelerator (LWFA). We calibrate deposited dose from the sound-wave amplitude, determine material-specific acoustic resonances from the Fourier transform of the acoustic waveform, and recover the absorber’s size and shape from 3D image reconstruction. First, phantom targets consisting of metal wires or slabs immersed in water were examined. Fourier decomposition of the pressure signal showed sharp frequency peaks that matched the expected eigenfrequencies from analytical solutions. These eigenfrequencies are linked to the density, speed of sound, and shape of the objects. Here, we used them to distinguish W, Cu, and Pb components of the targets, and accurately reconstructed the shape of wire grids and twisted wires. Next, electron irradiation of a bone sample immersed in water yielded ultrasound reconstructions that clearly distinguished the hard outer cortical bone, and matched the shape and size obtained from standard x-ray tomography. Finally, electrons irradiation of a kilogram of pork yielded ultrasound reconstructions that revealed preferential energy deposition in fatty tissue. Moreover, the acoustic response scaled linearly with number of shots, showing that this technique can provide real-time dosimetry in conjunction with very-high-energy electron (VHEE) therapy. All these cases are backed by simulations of the energy deposition using Monte Carlo simulations (GEANT4) and acoustic propagation (k-wave toolkit).

Speaker: José Franco Altamirano (The University of Texas at Austin)

81 The Ultra-Compact FEL: High Imapact Application to

The ultra-compact X-ray FEL (UC-XFEL) is an extremely attractive path for creating intense, coherent, short-wavelength light pulses. This scheme uniquely utilizesThe very high gradient cryo-RF for generating very high brightness electron beams, and accelerating thdm in short distances to GeV-class energy - both enabled by peak fields near 250 MV/m. This approach further permits use of very short-period undulators, permitting a 1 nm high performance FEL driven with a 1 GeV beam. While the original pro proposal was aimed at soft-X-ray science, recently this collaboration has pivoted to development of a hard X-ray (above 9 keV) version of the UC-XFEL that is aimed at transforming inspection techniques for next-generaty chips via ptychographic laminography - 3D imaging with few nm resolution. This development has been funded by the US DOE to study the commercial design, leading to the founding in 2025 of a new company. Ptyko, Inc., aimed at rapid commercialization of this technology. We describe this instrument and its revolutionary approach to imaging. As a stepping stone the hard X-ray machine, we plan to develop a 13.5 nm compact FEL for actinic inspection and review of lithography masks, utilizing ptychography to gain a dramatic advantages in image quality and processing.

Speaker: James Rosenzweig (UCLA Dept. of Physics and Astronomy)

82 Single-event effect microelectronics testing using a compact laser-plasma accelerator electron source

Single-event effects pose a significant concern for the reliability of electronic systems in radiation-intensive environments, such as avionics, space, and high-energy physics applications. Current single-event effect testing of microelectronics relies on heavy ion test facilities with limited accessibility and critical limitations in achievable penetration depth and energy deposition. Electron
sources could offer a powerful complement to these capabilities, providing both deep penetration, which depends on the beam energy, and tunable energy deposition, which depends on the bunch charge. Here, we report the commissioning and inaugural test results of a laser-plasma accelerator (LPA) electron source specifically designed for the needs of single-event testing and correlate them with established heavy-ion benchmark data.

This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and the Defense Advanced Research Projects Agency (DARPA) under the ASSERT Program, grant number HR001124C0411.

Speaker: Sarah Schröder (Lawrence Berkeley National Laboratory)

15:30 Coffee Break

A1-Working Group # 1

83 Dephasingless laser wakefield acceleration in a plasma waveguide

Laser wakefield accelerators (LWFAs) provide extremely large accelerating gradients for compact electron accelerators and radiation sources but are limited by dephasing, where trapped electrons outrun the accelerating phase of the wakefield. While flying-focus pulses can eliminate dephasing by driving a wake at the vacuum speed of light, these pulses involve tradeoffs such as varying spot sizes, longer durations, or larger plasma volumes. Here we show that spatiotemporally structured laser pulses can drive a wake at the vacuum speed of light in a plasma waveguide while maintaining a near-constant spot size and ultrashort duration, greatly reducing the required plasma volume. The pulses are constructed by superposing plasma-waveguide modes with appropriately selected frequencies. Scaling laws indicate that this approach can increase the single-stage energy gain by an order of magnitude over conventional LWFA. The periodic intensity peaks of the pulses may also benefit multi-pulse LWFA schemes, in which a train of pulses separated by the plasma period continually enhances the wakefield.

Speaker: John Palastro (Laboratory for Laser Energetics)

84 CHEQUP: an open-source hydrodynamics framework for plasma-channel formation

Plasma channels formed by hydrodynamic expansion of optical field-ionized (HOFI) plasmas evolve on timescales that are computationally expensive to model using fully kinetic Particle-In-Cell simulation. Predictive modeling of HOFI plasma channels requires multi-species, multi-temperature compressible hydrodynamics with self-consistent ionization, recombination, and collisional energy exchange between electrons and heavy particles, as well as coupling to particle-in-cell codes used downstream for wakefield modeling.

In this talk, we present the Castro-based Hofi Expansion with QUasineutral Plasma (CHEQUP), an open-source plasma-hydrodynamics framework built on the AMReX-based Castro code. CHEQUP solves the two-temperature compressible equations for a partially-ionized, multi-species plasma with independently evolving electron and heavy-particle temperatures, following the same set of equations as [1]. Simulations are supported in 1D/2D/3D Cartesian and cylindrical geometries with full adaptive mesh refinement. The framework is interoperable with other open-source tools (e.g., via the openPMD standard), including the LASY laser propagation library and the WarpX, FBPIC and HiPACE++ particle-in-cell codes. Examples of modeling HOFI plasma channel formation for relevant experimental parameters using CHEQUP will be presented.

This research was supported by the U.S. DOE, Office of Science, Office of High Energy Physics under Contract No. DE-AC02-05CH11231, and funds from the UC Multi-Campus Research Programs and Initiatives of the University of California, Grant Number M23PR5854.

[1] Mewes et al., “Demonstration of tunability of HOFI waveguides via start-to-end simulations”, Phys. Rev. Research 5, 033112 (2023)

Speaker: Christian McCombs (Lawrence Berkeley National Laboratory)

85 Hydrodynamic optical-field-ionized channel optimizations for beam brightness in a practical laser wakefield accelerator model

Laser wakefield accelerators (LWFA) have been experimentally demonstrated to yield high energy and charge density electron beams within a compact footprint, making these sources attractive for a number of applications. The electron beam energy from an LWFA is limited by the laser’s stability in plasma as described by a few length scales, the most constraining of which being the diffraction length of the laser. Hydrodynamic optical-field-ionized (HOFI) channels are an emerging technology used to increase the achievable energy by eliminating the diffraction length constraint of LWFA. These channels also efficiently utilize laser energy for beam acceleration, which makes them promising for industrial applications of multi-GeV electron beams when compared to unguided schemes. These HOFI-based plasma targets may be optimized for beam loading, acceleration, and efficient conversion of LWFA drive laser energy via Bayesian optimization. However, the added complexity of HOFI channels requires additional modelling steps to ensure that the plasma profiles passed to LWFA models embody realistically non-ideal systems. Here, we present a prototype LWFA Bayesian optimization pipeline incorporating hydrodynamic fluid simulations of plasma channel expansion, particle-in-cell simulations of LWFA, and simulations of the downstream transport lattice. We present a resultant plasma density profile that is optimal for LWFA with an axicon-produced HOFI channel, as discovered via Optimas and FBPIC.

Speaker: Christopher Doss (Inversion Semiconductor)

86 Scaling laws for guided and unguided laser–plasma accelerators at fixed laser energy and wavelength

Laser–plasma accelerators (LPAs) can operate in different regimes, namely guided regimes—where laser guiding is achieved by means of an external waveguide such as a plasma channel—and unguided regimes, where the laser is self-guided over the plasma length. For a given (fixed) laser driver energy and wavelength, guided and unguided LPAs exhibit distinct accelerating gradients, stage lengths, optimal bunch parameters, and acceleration efficiencies.

In this talk, we present a systematic investigation of the properties of guided and unguided LPA stages under fixed laser energy and wavelength. We derive and discuss scaling laws for their key characteristics as a function of laser energy and wavelength, and provide estimates of the maximum energy gain achievable with such accelerator stages.

Speaker: Carlo Benedetti (LBNL)

87 Optimizing Laser Parameters For Blowout Regime: From Petawatt NIR to LWIR Wakefield Drivers

Laser wakefield acceleration (LWFA) at low plasma density, $n_e \lesssim 10^{17}\,\mathrm{cm^{-3}}$, is highly desirable for generating high-energy electron beams because key accelerator figures of merit, including dephasing length and attainable energy gain, improve favorably as density is reduced. Near-infrared petawatt lasers provide a powerful route to high-energy LWFA stages in this regime, but efficient acceleration over practical distances requires driving a large-amplitude wakefield whose strength is governed by the degree of electron evacuation as well as the size of the plasma structure, the latter primarily determined by the laser spot size. Although $a_0 > 2$ is commonly used as a benchmark for accessing the highly nonlinear blowout regime, this criterion alone does not capture the critical roles of spot size and pulse duration nor the interplay among these quantities in LWFA physics; consequently, the short pulse durations and typical focusing conditions of near-infrared petawatt systems are not necessarily optimized for driving the high-amplitude, low-density blowout structures. This broader parameter dependence motivates a comparison with long-wavelength infrared drivers, such as CO$_2$ lasers, which naturally operate with pulse durations and focal geometries well matched to large low-density wakes. In this talk, we illustrate the critical roles of pulse duration and laser spot size in petawatt-class LWFA experiments aiming to access the highly nonlinear blowout regime. We further demonstrate the advantage of LWIR laser drivers in this parameter space, showing that a 15 TW, ~500 fs CO$_2$ laser pulse at $n_e = 2 \times 10^{16}\,\mathrm{cm^{-3}}$ can drive wakefields three times stronger than those obtained for BELLA- and ZEUS-scale petawatt lasers under similar conditions. This work was supported by the National Science Foundation under Grant No. PHY-2238840, U.S. Department of Energy, Office of Science under Award No. DE-SC-0014043 and resources of NERSC facility, operated under contract No. DE-AC02-5CH11231.

Speaker: Navid Vafaei-Najafabadi (Stony Brook University)

88 PIConGPU - coupling HPC and AI for laser plasma simulations

We report on new developments of the PIConGPU code with regards to coupling laser plasma accelerator simulations to large-scale AI models, ML-assisted date reduction, ML-guided optimization and surrogate modeling.
We report research highlights in laser acceleration of electrons and adjacent fields to showcase the breadth of applications covered by PIConGPU. Specifically, we report on extending the Traveling Wave Electron Acceleration Scheme towards staging, diagnostics integration for beam reconstruction and optimization for applications such as compact FELs.
We discuss how the integration of AI with HPC fosters progress in these applications beyond laser-driven lepton acceleration, e.g. for laser ion acceleration. We discuss the importance of common input/output standards for this and conclude by an outlook towards coupling simulation and experiment.

Speaker: Michael Bussmann (Helmholtz Zentrum Dresden Rossendorf)

A4-Working group # 4

89 High Power Test of Ultra-Short High Gradient Cavities via RF Pulse Compression

High brightness electron beams have a wide range of applications ranging from accelerator-based light sources to ultrafast electron diffraction and microscopy. Brighter beams can be generated by increasing the accelerating gradient on the cathode at the time of photoemission, making high gradient photoinjectors an important tool. One possible path to simultaneously achieve high gradient and suppress breakdowns is to reduce the RF pulse duration fed into the photoinjector to less than 20 ns. This led us to propose the Compressed Ultrashort Pulse Injector Demonstrator (CUPID), a 1.6 cell photogun driven by nanosecond-scale high power rf pulses to achieve high gradients with low breakdown rate. We report on the first high power tests of photogun-like RF cavities designed to harness these short pulses uniquely powered by a new 11.424 GHz SLED-type RF pulse compressor. We present details on the design and fabrication of these cavities along with the experimental setup used to test them. High power tests demonstrated pulses with peak power up to 166 MW per cavity, generating about 400 MV/m on the surface of the cathode. The early conditioning results show a viable route to reaching the high-gradient, ultra-short pulse regime for accelerators and photoinjectors using RF pulse compression.

Speaker: Ankur Dhar (SLAC National Accelerator Lab)

90 CUPID Photo-Injector Design and Beam Dynamics

High gradient radio frequency (rf) driven photoguns are photoemission electron sources that have important applications for accelerator-based instruments, such as light sources and electron microscopy. Numerous efforts have been made to push for even higher field gradient while suppressing rf breakdowns. We propose the Compressed Ultrashort Pulse Injector Demonstrator (CUPID), a 1.6 cell photogun driven by nanosecond high power rf pulses to achieve high gradients with low breakdown rate. This photogun is powered by ultrashort pulses from a rf pulse compressor and a high power klystron. This presentation focuses on the work of applying the CUPID photogun for the generation of x-ray free-electron laser at 40 keV photon energy or higher. We first present the design of CUPID photogun and designed performance to achieve very high field gradient, followed by beam dynamics studies of a photoinjector formed by CUPID photogun and other beamline components. Start-to-end simulation results with the existing LCLS copper accelerator are shown to demonstrate CUPID as a viable upgrade pathway for higher x-ray photon energies.

Speaker: Wei Hou Tan (SLAC National Accelerator Laboratory)

91 High Gradient Testing of a Two-Cell C-band Accelerator Cavity with NiCr Higher-Order Mode Absorbers

This presentation will report on the status high gradient testing of a two-cell accelerator cavity with distributed coupling and higher-order-mode (HOM) damping slots covered with nickel-chromium (NiCr) absorbing material. The cavity is designed with a specific purpose to demonstrate applicability of NiCr material for damping HOMs in a C-band distributed-coupling accelerating structure, such as may be used in a C3 linear collider. The purpose of this experiment is to conduct a simple high-power test to understand fabrication challenges for the cavity with NiCr HOM absorbers and examine performance of the NiCr coating during high power conditioning. We will report the detailed electromagnetic and engineering design of the cavity, fabrication, cold testing, tuning, the results of high gradient testing at the CERF-NM C-band high gradient test facility at Los Alamos National Laboratory, and the results of the post-mortem inspection under a scanning electron microscope.

Speaker: Evgenya Simakov

92 High gradient testing of the C-band 1.6 cell all-copper photoinjector

This presentation will report on the status of the high gradient testing of a 1.6-cell C-band RF photoinjector at Los Alamos National Laboratory (LANL). The construction of the Cathodes And Radio-frequency Interactions in Extremes (CARIE) C-band high gradient photoinjector test facility began in October of 2022. CARIE will house a high gradient copper RF photoinjector and other high gradient C-band accelerating structures (e.g., multi-cell cryo-cooled accelerating structures). The 50 MW 5.712 GHz Canon klystron powers the facility. The klystron was installed and conditioned in 2024. The output of the klystron is connected to a circulator that was conditioned to operate for up to 12 MW of power. The WR187 waveguide line brings the power from the circulator into a concrete vault that is rated to provide radiation protection for electron beam powers up to 20 kW. The 1.6 cell RF photoinjector was designed with optimized cell shapes to reduce peak surface fields and distributed coupling with the goal to demonstrate operation at the electric field of 240 MV/m at the cathode. The first injector was fabricated entirely of copper and does not have cathode plugs. This injector is installed at the end of the waveguide line and is under commissioning. High gradient commissioning of the photoinjector will validate operation of the CARIE facility and demonstrate that 240 MV/m accelerating field on the cathode can be reliably achieved. The status of the facility, the designs of the photoinjector and the beamline, and status of the high-power testing of the injector and other C-band components and cavities will be presented.

Speaker: Evgenya Simakov

93 Experimental Investigation of RF Breakdown in a Short-Pulse X-band Cavity

RF breakdown remains one of the principal limitations to high-gradient operation in normal-conducting accelerating cavities. Although breakdown under conventional long-pulse operation has been extensively studied, its behavior in the nanosecond short-pulse regime remains comparatively unexplored. In this regime, reduced pulse duration is expected to influence the development of field emission, surface heating, electron multiplication, and plasma formation, thereby modifying the onset of breakdown. To investigate these effects experimentally, a dedicated single-cell X-band cavity has been developed for high-power testing at the Argonne Wakefield Accelerator (AWA). The experiment operates with adjustable RF pulses in the few-nanosecond range and is equipped with diagnostics for RF signals, cavity fields, and time-resolved dark current measurements. We present the cavity design, low-power characterization, and the experimental diagnostic setup, supplemented by high-power test results as available. These results provide experimental insight into breakdown onset in the short-pulse regime and help establish the operating limits of high-gradient X-band cavities under nanosecond excitation.

Speaker: Gaurab Rijal (Northern Illinois University)

94 Breakdown analysis and wakefield simulation for the RF cavities in the muon collider ionization cooling channel

Ionization cooling is critical for a muon collider aiming to achieve high-luminosity collisions. In the cooling channel, the reference lab-frame relativistic β is between 0.88 and 0.93, a regime in which space charge effects cannot be ignored. The beam waist also varies substantially along the cooling lattice, suggesting that space charge effects may change significantly throughout the channel. In this work, we use electromagnetic fields resolved with a commercial particle-in-cell code and an in-house post-processing method to compute the wakefields of a rigid muon beam with transverse waist determined by the design lattice. We show that the space charge contribution to the composite wake can become significant when the beam transverse size is strongly compressed in later stages of the cooling channel. In parallel, we assess the effects of realistic solenoid fields combined with accelerating cavity-mode fields on field-emitted dark currents, building on previous models developed to explain the increased probability of RF breakdown in magnetic fields. Using RF-Track, we simulate beamlet dynamics and evaluate how these combined fields influence particle transport and impact behavior. The results reveal changes in collision statistics and provide a more detailed picture of beam and dark-current dynamics under realistic cooling-channel field configurations.

Speaker: Dillon Merenich (Northern Illinois University)

A5-Working group # 5

95 Magnetic Field Measurements and Reconstruction of very Broadband Electron Spectrometer for Plasma Experiments

A very broadband, beta spectrometer, capable of measuring electron energy ranging from 1MeV to 100MeV has been developed and installed for UCLA’s MITHRA facility for plasma wakefield experiments. This spectrometer employs sextupole-like fields to strongly bend electrons into a scintillating screen. Due to the large and complex geometry of the magnet, the magnetic fields are difficult to precisely reconstruct. Furthermore, accurate magnetic field measurements are essential for low-error spectrometer measurements. We have previously developed a reconstruction algorithm that employs a k-nearest neighbors (KNN) search to locally fit harmonic polynomials. To this end, we present both the measurements and finer grid reconstruction of this novel electron spectrometer.

Speaker: Jack Phillips (University of California, Los Angeles)

96 Compact electron spectrometry for tens-of-GeV laser-plasma accelerators

Laser-plasma accelerators (LPAs) of cm length, driven by petawatt lasers, now produce quasi-monoenergetic electron bunches of ~ 10 GeV in energy [1, 2]. New generations of experiments in emerging multi-PW facilities are expected to reach far greater energies, e.g., simulations show ~100GeV energy gain using 500J laser pulses in a single sub-meter stage[3, 4]. A new suite of diagnostics that match the compactness of the accelerators, without compromising accuracy and affordability, is desired. We report the design and performance of a compact magnetic spectrometer tailored to unique characteristics of quasi-monoenergetic, multi-GeV electron bunches from petawatt-laser-driven wakefield accelerators: mrad-level shot-to-shot pointing fluctuations, co-generation of betatron X-rays and of background electrons with a broad energy spectrum. The spectrometer replaces the first screen of a standard two-screen spectrometer with an array of thin, precisely-located, high-Z wires distributed throughout, and perpendicular to, the magnet’s dispersion plane. The thin, sharply-bounded shadows that they cast on betatron X-ray and electron signals enable determination of > 10 GeV electron energies and launch angles with few-% precision using a ∼ 1 T dipole magnetic field of ∼ 10 cm dimensions. Perturbations to the electron signals caused by hybrid acceleration mechanisms or inserted foils are also shown to be resolvable.
1. A. J. Gonsalves, K. Nakamura, J. Daniels, et al., Petawatt laser guiding and electron beam acceleration to 8 GeV in a laser-heated capillary discharge waveguide, Phys. Rev. Lett. 122, 084801 (2019).
2. C. Aniculaesei, T. Ha, S. Yoffe, et al., The acceleration of a high-charge electron bunch to 10 GeV in a 10-cm nanoparticle-assisted wakefield accelerator, Matter Radiat. Extremes 9.
3. K. G. Miller, J. R. Pierce, et al., Dephasingless laser wakefield acceleration in the bubble regime, Scientific Reports, Vol. 13, Iss. 1, (2023): 21306. DOI:10.1038/s41598-023-48249-4
4. J. L. Shaw, et al., 100-GeV Electron Beam via a Flying-Focus-Driven Laser-Plasma Accelerator, ArXiv: arXiv:2505.00157 (2025)

Speaker: Rafal Zgadzaj (University of Texas at Austin)

97 Calorimetry for Multi-GeV Wakefield Accelerators

For the next generation of high-power lasers, like ZEUS and MTW-OPAL, electron energies from 10 GeV to 100 GeV are expected. Conventional magnet spectrometers will have a huge footprint in the laboratory at these energies to maintain resolution, compromising the compactness of by plasma-based accelerators. Because of this, new ways to measure multi-GeV electron spectra will need to be developed.
Electromagnetic calorimeters are well-established detectors in the high-energy physics community, where they are used to characterize leptons and photons created in a collision event. The length of these detectors scales logarithmically with incoming energy, requiring up to 30 radiation lengths to stop particles even at TeV energies (lead, for example, has a radiation length of 5.6 mm). As high-energy leptons or photons enter a calorimeter, they create a particle shower dominated by bremsstrahlung and pair production. The shape of the shower depends on the energy of the incoming radiation.
We have designed sampling calorimeters for wakefield accelerators using alternating layers of lead and scintillating fibers. With the help of GEANT4 simulations we have developed a methodology using the transverse and longitudinal evolution of the shower to characterize beams at the GeV level. Preliminary experimental results obtained at the 10 PW beamline at ELI-NP suggest that electrons above 5 GeV were measured in the calorimeter, in good agreement with measurements from a magnet spectrometer.

Speaker: José Franco Altamirano (The University of Texas at Austin)

98 Indirect Characterization of Photoinjector Parameters and their Correlations

The development of high brightness RF photoinjectors for advanced accelerator applications necessitates a precise understanding of the initial beam distribution and physical parameters of the electron source. Traditional analysis of the solenoid scan technique fits the measured transverse spot sizes of the electron beam with a simplified analytic model to characterize the phase space at the exit of the RF gun. In this work, we demonstrate how combining a simulation-based beamline model with Markov Chain Monte Carlo (MCMC) techniques extends our understanding of photoinjector performance. By applying this Bayesian approach to experimental solenoid scan data, we recover posterior probability distributions for unmeasured or difficult-to-measure parameters, such as the photocathode Mean Transverse Energy (MTE) and the cathode longitudinal position within the re-entrant RF gun cavity. Importantly, the analysis reveals the multidimensional correlations and degeneracies between parameters, providing a deeper physical understanding of the coupled dynamics required to optimally characterize and control advanced high-brightness photoinjectors.

Speaker: David Garcia (UCLA)

99 Magnetic sextupoles for gamma and electron spectrometers

Higher-order magnets offer both advantages and challenges when applied to magnetic spectrometer design. We present an update for the CPT Compton spectrometer delivered to FACET-II and also initial results for the BPT 1-100 MeV single-shot electron spectrometer installed at UCLA's MITHRA lab. Both devices are based on a sextupole design which offers a broad energy range and horizontal focusing.

Speaker: Brian Naranjo (UCLA Dept. of Physics and Astronomy)

100 Spectral deconvolution of compound x-ray distributions for use in a high-repetition facility.

High-intensity laser–plasma interactions generate bright, energetic x-ray radiation via numerous mechanisms during the ultra-short lifetime of the interaction. X-ray radiation from these sources is both informative of the underlying processes and valued for secondary applications. Yet, absolute characterisation of this radiation remains a significant challenge owing to its variable brightness, ultrashort duration, broad spectral content, and the harsh background environment.
Typically, measurement techniques for high energy x-rays rely on absorption filters and an a-priori assumption of the spectral shape. This technique can be powerful but has distinct limits – a) the search space increases by the power of the number of free parameters in the assumed distribution, b) there is always a minimum for fitting routines irrespective of the accuracy of the initial distribution.
Exhaustive scanning and optimisation of the parameter space to return a “best-fit” with the measured data can be prohibitive for upcoming high-repetition, high-power facilities. Herein, we present two distinct methods to address this challenge; an analytical approach to reduce the number of parameters, and a neural-network machine-learning method that minimises a-priori assumptions. Throughout we discuss the applicability of these techniques to work in high-repetition facilities.

Speaker: Chris Armstrong (Central Laser Facility)

A7-Working group # 7

101 Optimizing photon collider through scattering laser wavelength selection.

A photon collider to access the 10 TeV parton-center-of-momentum (pCM) energy frontier of particle physics may enable the study of physics phenomena beyond the Standard Model. This collider, based on compact linear wakefield accelerator technology, could be realized through Compton scattering of multi-TeV lepton beams and moderate intensity laser pulses close to the collider interaction point. It is shown that for a large range of scattering laser wavelengths, even for those that cause prolific conversion of high energy photons into electron-positron pairs, photon collisions at the interaction point meet the luminosity requirements for novel particle physics studies. This is notable since the electron-positron pair production during the interaction of the scattering laser with the multi-TeV lepton beam leads to a natural limit on the maximum achievable photon luminosity. Moreover, these secondary pairs themselves can be utilized in physics studies since their luminosity is sufficiently high to produce heavy particles at rates needed for discoveries well beyond the reach of existing colliders.

This research was supported by LDRD funding from LBNL provided by the Director and the U.S. DOE Office of Science Office of HEP under Contract No. DE-AC02-05CH11231.

Speaker: Stepan Bulanov (Lawrence Berkeley National Laboratory)

102 Progress Updates from the 10 TeV Wakefield Collider Design Study

The 10 TeV Wakefield Collider Design Study, established in response to the 2023 P5 Report, has made significant progress since the study was announced at AAC 2024. Formed by a global community of particle theorists, HEP experimentalists, and accelerator scientists across national laboratories and universities, the Design Study has assembled dedicated working groups spanning LWFA, SWFA, and PWFA accelerator technologies, beam-beam interactions, beam delivery systems, detector concepts, and physics goals. Physics cases for electron-positron, electron-electron, and photon-photon collisions at 10 TeV center-of-mass energy have been initiated, with beamstrahlung effects included in these studies. We highlight several important results and publications from this past year. Looking ahead, we discuss synergies between the 10 TeV Design Study and on-going efforts in Europe--ALEGRO, HALHF, and ALIVE--and how these studies may co-evolve in the future.

Speaker: Jens Osterhoff (Berkeley Lab)

103 Laser-Based Collimation of Beam Halo Electrons via Compton Scattering

The design of future circular colliders will push beam currents and luminosities to unprecedented levels. Beam halo surrounding the main beam can deposit enough energy to melt conventional metal collimators and damage downstream components within a short time. Such damage was already observed during SuperKEKB commissioning [1]. A possible solution is to use Compton scattering to deflect halo electrons, effectively using a laser as a non-material collimator [2].

Previous studies have explored laser-Compton scattering for beam-intensity control in FCC-ee and laboratory tests at FACET-II [3,4]. In this work, we instead focus on laser-based halo collimation using tailored annular intensity profiles. We compare several schemes for generating donut-shaped beams, including axicons and spiral phase plates, and evaluate their suitability for different interaction geometries. We perform numerical analyses of the laser beam profile and single-electron scattering probability using SLAC FACET-II laser parameters. Based on these results, we propose a near-term experimental plan to test this concept in an upcoming FACET-II beamtime.

[1] S. Terui et al., “Collimator challenges at SuperKEKB and their countermeasures using nonlinear collimator,” Phys. Rev. Accel. Beams 27, 081001 (2024). https://doi.org/10.1103/PhysRevAccelBeams.27.081001

[2] F. Zimmermann, “New final focus concepts at 5 TeV and beyond,” AIP Conf. Proc. 472, 103–117 (1999). https://doi.org/10.1063/1.58898

[3] F. Zimmermann and T. O. Raubenheimer, “Controlling e+/e− circular collider bunch intensity by laser Compton scattering,” in Proc. IPAC’22, Bangkok, Thailand, pp. 1695–1698 (2022). https://doi.org/10.18429/JACoW-IPAC2022-WEPOST010

[4] C. Munting, P. Kicsiny, E. Barbi, N. Gonzalez, S. Gessner, and I. Drebot, “Laboratory Tests of Laser Control of Electron Beams for Future Colliders,” arXiv:2601.19865 [physics.acc-ph] (2026). https://arxiv.org/abs/2601.19865

Speaker: ChingEn Lin (Stanford University/ SLAC National Laboratory)

104 Synergies for Near-Term Colliders and Advanced Accelerator R&D

We highlight a number of activities that leverage the expertise and facilities of the Advanced Accelerator community for near-term collider R&D, with a specific emphasis on the FCC-ee. These activities include 1) pulse-to-pulse charge tuning for an RF gun, 2) emittance preservation in an injector linac, 3) laser-based collimation and control of high-energy beams, and 4) the application of Particle-in-Cell (PIC) codes for beam-beam collisions and strong field QED (SFQED) studies. FACET-II recently hosted users from CERN to test linac tuning algorithms that will be deployed in the FCC-ee injector. FACET-II is also supporting a laser-based collimation experiment that leverages the existing E-320 SFQED experimental infrastructure.

Speaker: Spencer Gessner (SLAC)

105 Coherent Phase Biasing of the Muon–Neutrino Transfer Channel as a Possible Path Toward Effective Muon Lifetime Enhancement

The finite lifetime of the muon remains one of the central challenges for energy-frontier muon colliders, motivating continued work in rapid acceleration, cooling, beam polarization, and mitigation of decay-induced detector backgrounds. We explore a complementary and highly speculative possibility: whether weak decay may be perturbed through coherent phase biasing of internal muon–neutrino transfer modes.

Within an impedance-network framework, the muon is modeled as a coherent multicomponent electromagnetic state whose internal degrees of freedom include scalar electric charge, vector magnetic flux quantum, and bivector magnetic moment. Weak decay is interpreted as coherent coupling of this parent state to a neutrino-sector transfer matrix containing vector magnetic flux, bivector electric flux, and trivector magnetic charge components. Particular attention is given to the electric–magnetic (eg) dyon channel, which provides a direct scalar–trivector coupling between the muon and neutrino sectors.

A longitudinal solenoidal magnetic bias is hypothesized to perturb selected internal phase relationships by an extremely small fractional amount relative to intrinsic particle field scales. However, if these local phase perturbations possess long coherence memory rather than resetting after each internal Compton-period particle–image oscillation, cumulative phase slip may develop over ~10^19 internal cycles during the laboratory-frame lifetime of a relativistic muon. Under such conditions, weak-decay phase closure may be detuned despite the small external perturbation.

Order-of-magnitude estimates based on relativistically boosted muon lifetimes, neutrino oscillation coherence scales, and internal Compton frequencies are presented. We identify the physical assumptions required for cumulative phase memory, formulate the problem in terms of the muon–neutrino transfer matrix rather than isolated muon or neutrino sectors, and propose accelerator-based tests capable of falsifying the hypothesis.

Potential implications for muon-collider staging, beam polarization, and suppression of decay-induced backgrounds are discussed.

Speaker: peter cameron

106 Towards self-consistent simulations of colliders with BLAST

Future collider performance will be increasingly shaped by the complex dynamics at the interaction point (IP). Indeed, proposed and existing machines operate in regimes of unprecedented luminosity and beam-beam parameters. This demands high-fidelity and flexible modeling tools.

A key challenge is the development of simulation frameworks that remain reliable across diverse interaction regimes, including SuperKEKB, EIC, FCC-ee, muon colliders, gamma–gamma colliders, and advanced concepts such as wakefield-based accelerators. In this context, we present recent advancements in WarpX, a particle-in-cell code capable of modeling beam-beam interactions at the IP. We describe new developments, enhanced physics capabilities, and ongoing efforts to broaden accessibility to a wider user community.

We also discuss open challenges and present initial work toward a unified simulation pipeline that enables end-to-end modeling from beam dynamics to collision. Specifically, we couple the BLAST codes ImpactX (for long-term beam dynamics) and WarpX (for detailed IP physics).

Finally, we showcase visualizations of beam-beam simulations developed by four high school students as part of the Experiences in Research program at LBNL.

Speaker: Arianna Formenti (LBNL)

Poster Session Tuesday

Wednesday 29 July

Invited Talks

107 The global effort towards a 10 TeV muon collider

Muon colliders provide a path to high-luminosity lepton collisions at center-of-mass energies beyond the reach of existing collider technologies. Unlike protons, muons are elementary particles, so the full beam energy is available in the collision. Unlike electrons, muons emit significantly less synchrotron radiation, enabling compact circular machines at the multi-TeV scale. A muon collider operating at 10 TeV or above would provide substantial discovery potential through both direct searches and precision measurements beyond the Standard Model. In this talk, I will present an overview of the muon collider and the remaining technical challenges, with a focus on superconducting magnet technology. I will also discuss designs for muon collider demonstrators.

Speaker: Dr Karie Badgley (Fermilab)

108 Strong field focusing of high energy particles in beam-multifoil collisions

Focusing multi-GeV electron beams to extreme densities is central to accelerator physics, laboratory astrophysics, and strong-field quantum electrodynamics research. Conventional approaches relying on large magnetic assemblies are ultimately limited in achievable focusing power.

Here we report the first experimental observation of a fundamentally new focusing mechanism, in which a high-energy electron beam is focused by its own electromagnetic fields reflected from a stack of thin metallic foils via near-field coherent-transition-radiation. When the beam traverses a conducting foil, electromagnetic boundary conditions require the transverse electric field to vanish at the surface while reinforcing the magnetic field, resulting in a net focusing Lorentz force at the foil surface. Repeating this interaction across multiple foils produces strong focusing.

The experiment, performed at SLAC’s FACET-II facility, reveals strong, cumulative focusing across a broad range of beam configurations, enabled by the delivered 10 GeV, 1 nC, 10 Hz electron beam. The measurements closely agree with predictions from an analytical model and particle-in-cell simulations. These results demonstrate that multifoil focusing is a remarkably straightforward, self-aligned approach to extreme beam generation, opening a path to explore unprecedented regimes of beam-matter interaction and high-energy radiation.

Speaker: Dr Aimé Matheron (Helmholtz Institute Jena)

109 Exploring the possibility of emitting axions by intense lasers, FELs and electrons oscillating in LWFA.

The axion is a hypothetical particle associated with a possible solution to the strong CP problem and is a leading candidate for dark matter. In this talk we investigate the emission of axions by electrons accelerated by intense laser beams. We find the emission probability and energy within the WKB approximation for an electron accelerated by an electromagnetic field. As an application, we estimate the number of axions produced by electrons accelerated using two counterpropagating high-intensity lasers and discuss how they would be converted to photons to be detected. We find that, under realistic experimental conditions, competitive model-independent bounds on the coupling between the axion and the electron could be achieved in such an experiment. We compare the results with axion emission from intense lasers or FELs interacting with magnetic or electric fields. Finally, we investigate the possibility of parametric decay of a laser beam into a lower energy beam and an axion.

Speaker: Prof. Robert Bingham (STFC Rutherford Appleton Laboratory)

10:15 Coffee Break

Invited Talks

110 AAC within the Evolving HEP Landscape: Perspectives from OHEP

DOE perspective

Speaker: Derun Li (LBNL)

111 The EuPRAXIA project: a plasma-based accelerator user facility for the next decade

The talk will discuss the latest news about the status of the EuPRAXIA user facility, in particular regarding the plasma beam-driven pillar that will be realized at INFN - Frascati National Laboratory.
The start of the building construction is foreseen by the end of the current year and the first beam is expected in 2031.
Recent experimental progress achieved at the SPARC_LAB facility will be presented, along with an outlook on how these results will be reproduced within the framework of EuPRAXIA.

Speaker: Livio Verra (INFN - LNF)

112 UCLA & the Birth of Plasma Accelerators: From Dawson's Idea to a Worldwide Field

The field of plasma-based accelerators traces its origin to UCLA and, above all, to John Dawson — whose 1979 paper with Toshi Tajima proposed using an intense laser to drive a plasma wave capable of accelerating electrons at gradients thousands of times beyond conventional radio-frequency cavities. This talk follows that idea from its roots in Dawson's early plasma-physics work through four decades of experimental, theoretical, and computational advances that turned a bold proposal into a thriving international discipline. This is, above all, a story about people. The students and collaborators Dawson mentored built a scientific lineage now leading efforts around the globe. I will trace that lineage from the founding generation to the present day, where plasma-based light sources are beginning to move from concept to reality, and close with a few reflections for students entering the field today.

Speaker: Mark Hogan

Santa Monica Beach Excursion

Thursday 30 July

Invited Talks

113 Single-shot reconstruction of electron beam longitudinal phase space

Laser and plasma wakefield accelerators are promising for many applications such as future TeV electron-positron colliders and X-ray free electron lasers (XFELs). These applications require high beam quality in terms of energy spread, emittance, and shot-to-shot stability. To achieve high beam quality, one needs to precisely diagnose the beam dynamics during acceleration. This is difficult owing to the highly nonlinear acceleration process and the sub-µm and sub-fs resolution requirements. Here, we report on a single-shot method for reconstructing the longitudinal phase space of electron beams in laser wakefield accelerators based on experimental observation of distinct periodic modulations in the angularly resolved spectra. The modulated spectra arise from the direct interaction between an ultra-relativistic electron beam and laser driver in the presence of the wakefield. A constrained theoretical model coupled with a genetic algorithm was used to recreate the experimental electron spectra and fully reconstruct the longitudinal phase-space distribution of the electron beam with a temporal resolution of ∼1.3 fs. The reconstructred phase-space provides the slice energy spread of the electron beam, which is critical for assessing the viability of applications such as XFELs. In our specific experiment, the root-mean-square slice energy spread is bounded at 9.9 MeV, corresponding to a 0.9-3.0% relative spread, despite a ~100% overall energy spread relative to the GeV average electron energy. Particle-in-cell simulations demonstrate that the reconstruction method can also be applied to electron beams from traditional accelerators, direct laser-electron interactions in vacuum, or beam-driven plasma wakefield accelerators.

Speaker: Yong Ma (University of Michigan)

114 Experimental demonstration of Flying-Focus enhanced Thomson scattering

We report the experimental demonstration of a spatiotemporally engineered “chromatic Flying-Focus” laser pulse to enhance x-ray generation in relativistic Thomson scattering. Precise tuning of the group delay dispersion was used to match the velocity of the focus to the trajectory of a counter-propagating laser-wakefield-accelerated electron beam. This extended the Thomson-scattering interaction, leading to an enhanced x-ray yield. This approach allows for maximising the spectral density and brightness of the x-ray beam by orders of magnitude compared to equivalent focusing without chromatic control.

Speaker: Elias Gerstmayr (Queen's University Belfast)

115 Recent R&D on RF systems for muon collider ionization cooling complex

International Muon Collider Collaboration (IMCC) has been formed about 5 years ago picking up and continuing the long-standing R&D effort initiated by the US Muon Accelerator Program (MAP). Since then, significant R&D progress has been made in key areas of the muon collider, one of which muon collider ionization cooling complex and its RF systems will be reviewed in this talk. Development of the RF cavities for the muon cooling will be presented together with associated RF systems and RF power sources. Several challenges will be addressed including operation of the cavities at the highest possible accelerating gradients in the range of ~20 to 30 MV/m in strong magnetic fields up to 17 T, very high beam loading effects and very large RF frequency range from 704 MHz in the 6D-cooling channel down to few MHz at the end of the final cooling. In addition to the design challenges, fundamental physics related to the phenomenon of vacuum breakdown in strong magnetic fields will be discussed and some new ideas and possible theoretical and experimental program worldwide to address these challenges will be presented.

Speaker: Alexej Grudiev (CERN)

10:15 Coffee Break

Invited Talks

116 Plasma-based compression of electron beams

Producing electron beams with sub-femtosecond durations and ultra-high peak currents would enable new opportunities in applications ranging from strong field quantum electrodynamics and laboratory astrophysics to next-generation light sources. However, compressing electron beams to such short durations without compromising quality requires new techniques. In this talk, we explore a plasma-based compressor that utilizes the large acceleration gradients present in a plasma wakefield accelerator to imprint onto the beam an energy chirp several orders of magnitude larger than what can be achieved using conventional techniques. A downstream dispersive element converts this chirp into temporal compression. Using particle-in-cell and particle tracking simulations, we show that this technique enables bunch durations approaching 10 nm and peak currents nearing 1 MA. We then present experimental results demonstrating the chirping and compression of 10 GeV electron bunches in a beam-driven wakefield accelerator at the FACET-II facility at SLAC National Accelerator Laboratory. These initial experimental results, supported by simulations, highlight the potential of plasma-based compression for generating the ultrashort, high-peak-current beams required for the next generation of accelerator-driven science.

Speaker: Kelly Swanson (SLAC National Accelerator Laboratory)

117 High repetition rate LWFA with all-optical guiding for user experiments at ELI Beamlines

We present the results obtained with the implementation of all-optical guiding technique in the ELBA and ALFA laser Wakefield accelerators at ELI Beamlines. In ELBA, we demonstrate for the first time all-optical guiding starting from a single laser pulse (L3-HAPLS, 15 J, 30 fs), enabling electron beam energy up to 5 GeV. This scheme has been experimentally tested up to 8 J at 3.3 Hz repetition rate. Furthermore, we demonstrated two new injection techniques in guided LWFA, that have been used to unambiguously show dephasing-mitigated multi-GeV electron beams. The upgraded electron beam parameters have been offered to ELBA users for laser-electron collider experiments and laser-driven muon production. In ALFA, we achieved all-optical laser guiding at 1 kHz, using 10 mJ 15 fs ionization laser (FSYNC) to drive a 40 mJ 15 fs laser (L1-Allegra).

Speaker: Gabriele Maria Grittani

118 Spectrotemporal shaping of attosecond X-ray free-electron laser pulses

Attosecond pulses from X-ray free-electron lasers (XFELs) have opened the doors to atomic site-specific studies of the motion of electrons on their natural timescales. Attosecond XFEL experiments to date have operated in the impulsive regime, in which the incoming pulse is short enough that the exact pulse duration and structure does not affect the system dynamics. On the other hand, structured pulses with tunable spectrotemporal shapes allow us to push the bounds of our models of quantum systems and pursue coherent control schemes in the ultrafast, X-ray driven regime. I will discuss two types of attosecond pulse shaping in which an isolated attosecond pulse generated in one set of undulators is shaped in a second stage. In the first, I will show how undulator tapering can be translated into versatile control of the spectrotemporal structure of an FEL seeded by a short pulse. I give an example of experimental evidence of the production of mutually coherent attosecond pulse trains. In the second method, I show how leveraging microbunching generated in the first stage enables the production of mutually coherent attosecond pulse pairs. I show direct time-domain evidence that pulse pairs can be produced and that their relative time delay and phase are both stable and tunable.

Speaker: River Robles (Stanford University)

12:15 Lunch

A1-Working Group # 1

119 Experimental Demonstration of Laser Wakefield Acceleration Driven by Laser Pulse Carrying Orbital Angular Momentum

A laser beam carrying orbital angular momentum (OAM) is characterized by a helical wavefront, with an optical vortex in the center. Most applications of OAM laser beams, including optical prob-ing, particle manipulation, and communications, operate at relatively low intensities. Recently, high-intensity OAM beams have been generated using spiral phase mirrors, expanding their applicability in high-power laser-plasma experiments. Here, we present laser wakefield acceleration (LWFA) driven by relativistic optical vortex beams performed at the ZEUS Laser Facility. We observe high-energy electron beams with broadband spectra exhibiting distinct energy branches and correlated angular dispersion. Quasi-3D particle-in-cell simulations show agreement with the observed spec-tra, and further reveal helical electron trajectories within the ring-shaped wakefield. The results demonstrate the correlation between the helical phase structure of the driven laser pulse and the phase-space structure of the accelerated electron beam, and are consistent with angular momentum transfer between the laser driver and the accelerated electrons. This work demonstrates that OAM offers a new degree of freedom for structuring relativistic electron beams in LWFA.

Speaker: Qian Qian (University of Michigan)

120 Nonlinear propagation of spatiotemporal optical vortex pulses

Spatiotemporal optical vortex (STOV) pulses feature a circulation of Poynting flux around a co-moving phase singularity embedded in their spacetime structure. The transverse orbital angular momentum (OAM) arising from this circulation extends the concept of longitudinal OAM associated with pure spatial phase singularities, resulting in distinct linear and nonlinear propagation behavior. Here, we introduce an analytic model for the nonlinear propagation of STOV pulses in graded-index, anomalously dispersive media with an instantaneous Kerr response. Three types of STOVs are analyzed: perfect spherical STOVs, which preserve their shape in two spatial and one temporal dimension; perfect cylindrical STOVs, which preserve their shape in one spatial and one temporal dimension; and imperfect STOVs, whose profile evolves during propagation. For each type, the conditions for self-guiding and collapse are derived.

Speaker: Abram Konzel (University of Rochester Laboratory for Laser Energetics)

121 Ultrafast Angular Momentum Transfer in Tunnel-Ionized Plasmas

The transfer of angular momentum (AM) from circularly polarized or vortex laser beams to plasma offers a novel mechanism for controlling plasma morphology and self-generated fields. This work explores the collective plasma response initiated during tunnel-ionization, focusing on two ultrafast phenomena: spiral electron density modulation and axial magnetic field generation. Using an analytical model validated by 3D PIC simulations, we show that space-dependent electron drift motion induces transient spiral density structures. These evolve into spiral density waves and subsequent filaments via streaming instabilities. We identify these dynamics through Thomson scattering spectral signatures of the electron plasma waves. Additionally, the absorption of photon AM drives azimuthal currents, generating Tesla-level quasistatic magnetic fields. These results suggest that laser-driven AM transfer can substantially modify the plasma environment relevant to laser–plasma acceleration, where the resulting magnetic fields and density structures may influence beam transport, injection, and instability dynamics.

Speaker: Chen-Kang Huang (National Central University)

122 Plasma-based Powerful, Radially-polarized, Narrowband THz for Compact Electron Accelerators

Plasma is a promising medium for generating high-power terahertz (THz) pulses, as it can be driven by extremely intense laser fields without suffering permanent damage. Numerous approaches have been proposed to convert the energy of a driving laser pulse into THz radiation using plasma as the conversion medium. The schemes such as coherent transition radiation (CTR) or two-color method, where transient nature of electron currents are the mechanism, produce broadband THz pulses. On the other hand, more long-lasting plasma oscillation can be exploited for generation of narrowband THz waves. However, this latter approach has difficulty in achieving efficient coupling between the electrostatic plasma oscillation and the electromagnetic THz radiation. Recentaly we proposed a couple of methods to generate a localized plasma oscillators; a plasma dipole oscillation (PDO) [1], and radial plasma oscillator (RPO) [2]. The key aspects of those novel methods are in localizing the spatial region of the plasma oscillation, using colliding two detuned pulses (for PDO) or local resonant excitation of the plasma by colinear detuned pulses (for RPO). In this presentation, the main ideas and simulation results are introduced. In particular, the simulation of electron acceleration by radially polarized THz wave is introduced.
[1] K.B. Kwon et al., Sci. Rep. 8, 145 (2018).
[2] M. Kumar et al., Phys. Rev. Lett. 134, 015001 (2025).

Speaker: MinSup Hur (UNIST)

123 Investigation of transverse instability in efficient plasma-based accelerators

Plasma-based accelerators can sustain multi-GV/m accelerating fields, but the strong focusing forces within the plasma channel can amplify small initial offsets into severe transverse instabilities known as beam break up (BBU) instability. Lebedev et al. [1] established a universal efficiency-instability relation for the blowout regime, asserting that the beam energy spread required to suppress BBU via BNS damping becomes incompatible with collider-quality beams as power-transfer efficiency increases. In this work, we address this trade-off by proposing a theoretical framework on the wake potential to precisely determine the transverse force experienced by a beam loaded trailing bunch. By isolating the self-wake of the witness bunch through its scalar potential, we derive an exact analytical transverse wake function that inherently accounts for the structure of the loaded plasma bubble.

To investigate these dynamics in a high-efficiency regime that preserves beam quality (low emittance and low energy spread), we employ a specifically shaped trapezoidal trailing bunch designed to flatten the longitudinal accelerating field. Our theoretical model is rigorously validated against three-dimensional HiPACE++ Particle-in-Cell (PIC) simulations, demonstrating remarkable agreement and improved accuracy over previous transverse wake function models [1]. Utilizing our analytical framework, we perform a comprehensive parametric study for a 10 GeV plasma stage, mapping efficiency limits against stability thresholds as functions of the plasma bubble radius, the loaded field, and the bunch length. High-fidelity Particle-in-Cell (PIC) simulations within the identified high-efficiency, low-instability regimes show strong agreement with our theoretical predictions for both centroid oscillation and emittance evolution. These results identify a stable operating region in which the energy-transfer efficiency can approach 40%, while emittance growth remains modest and the relative energy spread stays near 1%. By providing a model to map these stable, high-efficiency operating points, this work offers a clearer path toward designing accelerators that maximize energy transfer while maintaining beam stability, contributing to the theoretical foundation required for future compact particle colliders.

References
[1] Lebedev, Valeri, Alexey Burov, and Sergei Nagaitsev. "Efficiency versus instability in plasma accelerators." Physical Review Accelerators and Beams 20, no. 12 (2017): 121301.

Acknowledgements
We acknowledge the support by U.S. Department of Energy, Office of Science under Award No. DE-SC-0014043, DE-SC-0024277 and resources of NERSC facility operated under Contract No. DE-AC02-5CH11231.

Speaker: Arohi Jain (Stony Brook University)

124 Gas-phase diffractive optics for high-power beam control

We demonstrated efficient gas-phase diffractive optics created by interfering deep-ultraviolet lasers in an ozone-doped gas flow. These gas optics exhibit damage thresholds above $1\,\mathrm{kJ/cm^2}$ and can be used to steer high-power laser beams. Additionally, we demonstrated spectral and coherent beam combining with gas optics. Our results suggest a potential pathway for constructing next-generation high-average-power high-repetition-rate laser drives for compact particle accelerators.

Speaker: Ke Ou (Stanford University)

A3-Working group # 3

125 Feasibility and Stability of PWFA Injection Schemes in Hybrid Plasma Accelerators

Hybrid plasma wakefield accelerators combine a laser wakefield accelerator (LWFA) stage with a particle-driven plasma wakefield accelerator (PWFA) stage, leveraging the complementary strengths of both approaches. The PWFA stage offers a robust way to improve the energy, stability, and beam quality of electron bunches produced by the LWFA. This makes the hybrid scheme a promising pathway for becoming a compact source for high-quality electron beams that can drive future light sources, such as free electron lasers. A key challenge in such systems is the sensitivity of the PWFA injection process to intrinsic jitters in the LWFA output. Using particle-in-cell simulations, we systematically investigate different PWFA injection schemes and characterize their stability in response to realistic jitter conditions of LWFA-produced electron bunches. Our results provide guidance for the design of robust hybrid accelerator configurations.

Speaker: Edgar Anton Hartmann (Heinrich Heine University Düsseldorf)

126 Multi-GeV Electron Combs from a Plasma Wakefield Accelerator

Plasma accelerators now deliver GeV-class electron beams with sufficient brightness and stability to drive free-electron lasers. Yet they offer a distinctive capability that remains largely unexplored: the phase space of a trapped beam can be shaped in situ, at the moment of injection, on femtosecond timescales. In this talk, we report the generation of multi-GeV electron combs in a plasma wakefield accelerator driven by a 10-GeV electron beam propagating through a helium-confined lithium heat-pipe oven. The comb is a beam consisting of more than ten microbunches spanning 2 to 6 GeV, simultaneously separated in energy and time. Each microbunch exhibits a percent-level energy spread, carries several pC of charge, and has sub-femtosecond length; the energy separation between adjacent microbunches reaches up to 10%. Two mechanisms combine to produce this structure: betatron-driven pinching of the trailing spike of the double-spiked drive beam triggers sequential ionization injection of helium electrons once per half betatron period, while the gentle lithium density gradient maps each bunchlet to a different wake phase. Electrons ionized over ~17 cm are thereby compacted into a beam only a few micrometers long, yielding a mapping factor over 26,000. This work establishes femtosecond, in-situ phase-space shaping in plasma accelerators, paving the way for structured electron beams with tailored energy-time correlations.

Acknowledgements. This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-76SF00515 (FACET-II) and Grant No. DE-SC0010064 (UCLA). Simulations used resources of NERSC under Contract No. DE-AC02-05CH11231 (Award HEP-ERCAP-MP113). S.C., C.A.L., and O.G.F. acknowledge support from ANR (ANR-23-CE30-0011), ERC (101116161), and NFR (313770), respectively.

Speaker: Chaojie Zhang (University of California Los Angeles)

127 Passive Plasma Lens Experiments at FACET-II

Powerful and compact beam transport systems are essential for plasma-based accelerators, and plasma lenses provide a promising path forward. While plasma lenses have demonstrated strong, axisymmetric focusing, their application to advanced beam manipulation—such as chromatic correction—remains largely unexplored. Here we report progress on a quasilinear passive plasma lens experiment conducted at FACET-II. In addition to achieving focusing gradients exceeding 200 kT/m, the lens reduces the spread of slice focal positions, yielding a near-common focus at 27 ± 4 cm downstream of the lens, compared to an initial chromatic distribution of 37 ± 12 cm. The lens is ultra-compact with only a submillimeter length along the beamline and preserves the energy spread of both drive and witness bunches at the per-mille level. Ongoing efforts in passive plasma lens research at FACET-II will also be discussed.

Speaker: Shutang Meng (Department of Physics, University of Colorado Boulder)

128 Proposal for FACET-III

FACET is a transformative facility that pioneered plasma wakefield acceleration. This contribution proposes ideas for the continuation of FACET-II, dubbed “FACET-III”, with a focus on ultrabright electron beams and light sources such as XFELs to serve a wide range of needs in Basic Energy Sciences, industry, accelerator and HEP R&D, and the international user community.
FACET is the only linac-based facility worldwide capable of providing dephasing-free 100 GV/m plasma wakefields driven by tens-of-kA, 10 GeV electron drive beams together with synchronized laser pulses. These capabilities enabled the first-ever demonstrations of density down-ramp injection in PWFA [1] and the plasma photocathode technique [2] as pathways toward ultrabright beams. The facility is uniquely suited for further development into a platform that simultaneously acts as a beam-brightness transformer and energy booster [3], while also functioning as a stability transformer [4].
If ultrahigh brightness operation were established as a central design backbone, FACET-III could produce multi-kA, dark-current-free, attosecond-scale electron beams with brightness orders of magnitude beyond LCLS. This would open a new research frontier and may enable XFELs with photon energies exceeding 60 keV already at 2.3 GeV and true diffraction-before-destruction imaging [5], imaging of electronic motion on their natural time and length scale [8], potentially extending toward several hundred keV at higher electron energies that are straightforward within reach with 10 GeV driver beams [6,9]. Such capabilities would strongly motivate and inspire advanced undulator development required to fully exploit the ultrahigh beam brightness, and overall act as condensation point for next-generation XFEL R&D co-located with LCLS and LCLS-II. Attosecond ultrabright electron beams and derived hard photon sources could also enable precision QED studies and many additional applications [7].
FACET-III as an ultrahigh-brightness machine would constitute a globally unique research infrastructure, filling a critical gap in the worldwide accelerator and light-source landscape.

[1] All-optical density downramp injection in electron-driven plasma wakefield accelerators, D. Ullmann et al.., Phys. Rev. Research 3, 043163, 2021
[2] Deng, Karger et al., Nat. Phys. 15, 1156–1160 (2019)
[3] Plasma photocathode beam brightness transformer for laser-plasma-wakefield accelerators, DOE SBIR DESC0009533 (RadiaBeam)
[4] Campbell et al.,Phys. Rev. Research 8, 013273 (2026)
[5] Habib et al., Nat. Comm. 14, 1054 (2023)
[6] https://indico.global/event/5645/contributions/45376/
[7] Applications enabled by plasma photocathode PWFA calibre XFELs are included in the UKXFEL Science Case, see https://www.xfel.ac.uk/
[8] https://www.energy.gov/science/bes/articles/ice-cold-plasma-electron-beams-prepare-power-future-hard-x-ray-laser-beams
[9] F. Habib et al., Plasma accelerator-based ultrabright x-ray beams from ultrabright electron beams," Proc. SPIE 11110, Advances in Laboratory-based X-Ray Sources, Optics, and Applications VII, 111100A (9 September 2019)

Speaker: Bernhard Hidding (Heinrich Heine University Düsseldorf / University of Strathclyde / The Cockcroft Institute)

129 Dark-field shadowgraphy for ultrasensitive probing of plasma accelerators, wakeless regime and filamentation instabilities

In experiments involving beam-plasma interactions, direct imaging techniques can serve as powerful tools for in situ visualization and analysis of plasma processes and parameters. An important example of direct imaging technique is shadowgraphy, which is based on optical modulation by plasma inhomogeneities. Major limitations of existing shadowgraphic techniques, however, are their complexity and poor sensitivity to small plasma density fluctuations. Dark-field shadowgraphy, a novel design based on schlieren principles, promises to deliver orders of magnitude higher signal-to-noise ratio with less stringent requirements on probe laser parameters.

To demonstrate the use of dark-field shadowgraphy in probing beam plasma interactions, we present preliminary results from two experimental campaigns at the FACET-II, SLAC. The first experiment (E340) aims at studying the transition between beam-driven plasma waves (PWFA) and a wakeless regime characterized by breakdown of periodic wave structures and formation of ion channel in a narrow plasma column. Implementing dark shadowgraphy, we observed a clear distinction between image patterns from the PWFA and wakeless regime with good agreement to expected plasma wave periods, numerical simulations, and other experimental measurements. The second experiment (E305) aims at characterizing filamentation instabilities formed by an ultra-relativistic electron beam interacting with a plasma background, the same physical process powering important astrophysical phenomena such as gamma ray bursts. First dark shadowgraphy images from the experiment indicated sensitivity to instability-forming conditions, promising use of the diagnostics in laboratory astrophysics platforms for probing beam plasma instabilities.

Speaker: Haiping Zhang (University of Colorado Boulder)

130 Effective-Action based approach to modelling plasma wakefields for use in rapid parameter scans and Optimization

The bubble regime of drive plasma wakefields is notoriously difficult from an analytical perspective due to the inapplicability of standard fluid theory and perturbative approaches. The most widely used model was developed by Lu and extended for improved accuracy in the rear of the bubble by Dalichaouch, this approach gave a 2nd order ODE for the ‘bubble radius’ with one or more phenomenological free parameters and initial conditions determined by PIC simulation data. Taking inspiration for the Lu-type model, we have developed a self-consistent theoretical framework that gives a relatively small closed set of ODE’s for the wake which has a direct correspondence to the kinetic quasistatic theory used in highly accurate PIC codes such as QPAD. This framework is ideal for use with standard ML libraries for rapid parameter scans and optimization. The approach is based on constructing the effective Lagrangian for only the radial coordinates of the plasma electrons by integrating out the fields. The fields can be recovered from the solution for the trajectories. The Lagrangian-based approach has the advantage that it allows for construction of further reduced models using constraint forces and generalized coordinates. The connection to the ‘energy conserving’ delta-sheath theory of Golovanov is given. Comparison of the wakes is also given.

Speaker: Elias Hansen (University of California, Los Angeles)

A5-Working group # 5

131 Emittance Growth and Sensitivity Analysis of a Transverse Deflecting Cavity-Based Dechirper

We present a linear chirp control approach consisting of transverse deflecting cavities and negative-identity drift sections. While the beamline supports both positive and negative chirp manipulation, we focus on operation that drives the beam toward a large positive chirp for applications such as broadband radiation generation and Balakin-Novokhastky-Smirnov damping for structure wakefield acceleration. Emittance growth in this beamline is analyzed with an emphasis on second-order and space charge effects. Based on the identified sources, we propose a design that preserves beam quality while imparting or correcting a large chirp. In addition, sensitivity to cavity phase and amplitude jitter is evaluated, and the resulting impact on beam position and chirp is characterized. These results establish design guidelines and practical tolerance levels for stable operation.

Speaker: Alex DeSimone (Northern Illinois University)

132 The EEX-enabled microbunching experiment at the Argonne Wakefield Accelerator

In the past year, a UCLA-NIU-ANL-LANL-SLAC collaboration has begun a dedicated experimental program investigating a technique to produce microbunching and associated coherent radiation by manipulating electron beams using the emittance exchange (EEX) beamline at the Argonne Wakefield Accelerator (AWA). This type of scheme, while awaiting first tests of its efficacy, underpins the ambitious compact short wavelength FEL program at ASU, the CXFEL project. The goal of this study is to experimentally determine the practical limits to create longitudinally pre-modulated electron beams, subject to collective effects such as space-charge and coherent synchrotron radiation. We give here an overview of the experimental setup, including beam optics layout, beam diagnostics, coherent radiation diagnostics. We review simulation and theoretical modeling issues, and discuss hardware development and near term run plans.

Speaker: Prof. James Rosenzweig (UCLA Dept. of Physics and Astronomy)

133 1-D plasma lens by laser-driven elongated wakefield.

Future linear collider concepts often use "flat beams" with high emittance asymmetry to reduce bremsstrahlung, together with extreme beam focusing to achieve high luminosities. Although plasma lenses provide superior focusing gradients, existing designs are limited by the current-carrying capacity of active capillary-based lenses or the cylindrical symmetry of underdense lenses. This symmetry introduces transverse coupling and triggers resonant emittance mixing, which rapidly degrades the flat-beam phase space and reduces luminosity. In this talk, we present a novel 1D plasma lens that overcomes these challenges by operating in a previously unobserved, focusing-dominated wakefield regime at a low plasma density. By employing a 2-3 $TW$, 2 $ps$ long-wavelength IR CO2 laser pulse, we generate a highly elongated, electron-depleted ion cavity in a plasma density of $3 \times 10^{15} cm ^{-3}$. The regime was observed with a 50-60 $MeV$ electron beam probe at the Accelerator Test Facility in Brookhaven National Laboratory. This configuration produces strong, linear transverse focusing fields while nearly extinguishing longitudinal accelerating fields. The resulting cylindrical ion channel focuses exclusively in one transverse direction, providing a decoupled focusing geometry that preserves the phase space of highly asymmetric beams with minimal emittance degradation. This 1-D plasma lens represents a critical step toward the robust focusing geometry that produces a flat beam without requiring significant initial mismatch in emittance for next-generation high-energy physics colliders.

Speaker: Apurva Gaikwad (Stony Brook University)

134 A Multi-Mode RFQ for Dual-Species and Short-Pulse Beam Production

A radio-frequency quadrupole (RFQ) was designed at 201.25 MHz for accelerating a proton (H+) beam and negative hydrogen ion (H–) beams from 65 keV to 2.1 MeV, for the LANSCE Accelerator Modernization Project (LAMP). The RFQ operates with a wide range of beam currents, from sub-mA currents for beamline tuning to 55 mA when producing high-charge bunches. To support a variety of experimental areas, the RFQ produces these beams with distinct timing patterns. In particular, the WNR facility requires one short-pulse H– bunch every 1.8 μs, calling for a unique operating mode of the RFQ for producing a ∼50-ns beam pulse, which is subsequently chopped in the medium-energy beam transport (MEBT) to retain only one single 201.25-MHz bunch. To accommodate the diverse operating modes while maintaining optimized beam quality and meeting the performance requirements of the project, the LAMP beamline also incorporates a dual-mode H– ion source, low-energy beam transport (LEBT) with multi-chopper beam control, and a specially designed MEBT.

Speaker: Haoran Xu (Los Alamos National Laboratory)

135 Chirp control of plasma-accelerated electron bunches via wake depletion

Plasma-accelerated electrons often develop percent-level time-correlated energy spread (''chirp") because the longitudinal accelerating-field changes across the bunch. Existing approaches to dechirping typically require precise tailoring of the density profile of the plasma or the injected bunch, or the insertion of chirp-control devices downstream of the wake. Here, using particle-in-cell simulations, we identify a dechirping mechanism that relies only on the natural shortening of a wake as its pump depletes, causing the on-axis field slope across the accelerating bunch to reverse sign and compensate the chirp. The mechanism operates over a broad range of plasma densities and injected beam charges and profiles. We observe reduction of energy spread $\sigma_E/E$ of an externally injected electron bunch from $\sim$1% at injection (50MeV) to a minimum of $\sim$0.25%, with the bunch reaching $\sim$650MeV at the dechirped minimum. We will discuss how the choice of drive pulse wavelength, plasma density, and injection mechanism influences the effectiveness of this de-chirping mechanism.

Speaker: YUXUAN CAO (University of Texas at Austin)

136 Laser Heater as a Beam Shaping Tool at FACET-II: From Microbunching Instability Suppression to Multi-Spike Current Profiles

At FACET-II, laser heater (LH) optimization, encompassing power, alignment, and timing, is employed to suppress microbunching instabilities and customize longitudinal current profiles. Analogous techniques at LCLS have demonstrated that temporally shaped LH pulses can imprint programmable slice energy spreads that, after bunch compression, convert into controlled current modulations, enabling attosecond lasing, bunch trains, and caustic suppression [1]. At FACET-II, we extend this paradigm toward plasma wakefield acceleration: tailored LH imprinting via short Gaussian modulations, combined with RF linac phase tuning, enables the controlled generation of multi-spike current profiles optimized for resonant plasma wakefield excitation, where the inter-spike spacing is matched to the local plasma period. Driving plasma wakefields resonantly with a current spike train enables coherent wakefield superposition and amplitude growth along the train, simultaneously increasing the accelerating gradient and the transformer ratio beyond the symmetric-driver limit, as recently demonstrated experimentally in the linear regime and proposed for extension to the nonlinear regime at FACET-II [2,3].

In this contribution, start-to-end simulations and machine-learning-guided scans over the joint LH power, LH profile, and RF linac phase space identify operating points producing well-separated, high-current spikes at the FACET-II plasma injector entrance [4], made experimentally accessible by a newly commissioned LH pulse stacker. We present simulation results alongside preliminary experimental characterization, establishing the laser heater as a flexible, shot-by-shot instrument for active longitudinal beam shaping at FACET-II.

[1] D. César and A. Marinelli, Phys. Rev. Accel. Beams 24, 110703 (2021)
[2] L. Verra et al., Phys. Rev. E 112, 045205 (2025)
[3] C. Emma et al., Phys. Rev. Lett. 134, 085001 (2025)
[4] N. Sudar and Y. Ding, arXiv:2208.03973 (2022)

Speaker: Anna Kinderman

A6-Working group # 6

137 Nonlinear Inverse Compton Scattering experiments enabled by Long-Wave Infrared Laser in BNL ATF

Status and capabilities of nonlinear Inverse Compton Scattering (ICS) experiments at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF), utilizing a 9.3 µm Long-Wave Infrared (LWIR) CO2 laser is reported. Decades of long feasibility studies continue to expand further, through an upgraded multi-TW LWIR laser and optimized 85 MeV electron beam. Benchmarked laser parameters obtained in Orbital Angular Momentum X-ray study utilizing circularly polarized LWIR laser is introduced. Efforts to minimize relative timing jitters associated with low level RF to high power RF across all key locations, with potential feedback controls, is under consideration required by multiple beam interaction experiments such as Bi-harmonic ICS to maximize luminosity efficiently.

Speaker: Yusuke Sakai (Brookhaven National Lab)

YSakai_2026_AAC_V092.pdf

138 The STAR Project: Status of the Commissioning of the Compton Light-Source Infrastructure in Southern Italy.

The conditioning and initial commissioning activities of the STAR (Southern Europe Thomson Back-scattering Source for Applied Research) facility are currently underway at the University of Calabria in southern Italy. STAR is a compact X-ray source based on inverse Compton scattering (ICS) between a relativistic electron beam and an intense laser pulse. During this initial phase, all major subsystems have been installed, tested, and brought into operational condition, enabling the first acceleration of electron beams and the successful transport of both the electron and laser beams to the interaction point.
Electron acceleration is achieved using an S-band RF photoinjector followed by an S-band linear accelerator and two C-band accelerating structures. This configuration allows electron bunch energies to be tuned between 60 MeV and 150 MeV. The UV-laser–driven electron beam has reached energies up to about 100 MeV, able to reach 150 MeV with charges exceeding 200 pC and a temporal duration of approximately 5 ps (FWHM). In parallel, the high-energy infrared laser pulse (500 mJ, 5 ps) has been transported and characterized at the interaction point with a scanning resolution over the electron beam below 1ps.
Once fully operational, STAR is designed to operate as a user-oriented light source providing monochromatic, tunable, and polarized X-ray radiation. The system will generate picosecond X-ray pulses with photon energies in the range of 40–350 keV. The STAR project, including its planned high-energy upgrade, has been developed in collaboration with the Istituto Nazionale di Fisica Nucleare (INFN) and is coordinated by the INFN National Laboratories of Frascati together with the INFN Milan Division and the LASA laboratory.
The results obtained so far represent a key milestone toward the generation and optimization of ICS X-rays at the STAR facility.

Speaker: Luigi Faillace (Italian National Institute for Nuclear Physics (INFN))

139 Inverse Compton X-ray Source Commissioning at RadiaBeam

RadiaBeam Technologies has commissioned, characterized, and begun demonstrating applications of a highly tunable inverse Compton scattering (ICS) X-ray source based on a 100 MeV-class C-band electron linac. The photoinjector features a hybrid structure achieving sub-picosecond bunch compression within a compact footprint, suitable for a containerized final size. Two C-band linacs with adjustable RF power accelerate a 250 pC beam to between 30–95 MeV, with energy tunability achieved by adjusting the RF power balance between the two accelerating sections. Energy spreads of less than 0.5% rms were measured using a 45° dipole across the full energy range. Sub-micron normalized emittance was measured at 94 MeV via quadrupole scan, in good agreement with digital twin simulations and initial design work. Beam stability was studied as a function of the low-level RF subsystem, and active low-frequency fluctuation compensation was introduced into the control system.
The interaction laser is a picosecond 1030 nm pulse delivering up to 18 mJ to the interaction point, where both laser and electron beam are focused to spot sizes of σ < 30 μm. The nearly head-on electron-photon collision (3° crossing angle) produces X-rays with peak energies tunable from 30 keV to 100 keV, with up to 10⁵ photons per shot. X-ray photon count, beam divergence, spatial-spectral coupling, and local bandwidth have been measured across the tunability spectrum, with results generally agreeing with theoretical predictions and simulations.
Applications of the ICS source have begun to be explored, including successful demonstrations of K-edge imaging using elemental foils spanning from Ag (Z=47, K-edge at 25.5 keV) to Pb (Z=82, K-edge at 88.0 keV), showing clear material discrimination and spatial absorption contrast only achievable with high-quality, sub-picosecond electron bunches. Active efforts are also underway to focus the X-ray beam to micron-scale spot sizes for material and device inspection. Broader applications in fields such as medical imaging are being pursued.

Speaker: Maksim Kravchenko (RadiaBeam Technologies)

140 Energy-resolved measurement of individual GeV muons from the BELLA PW Laser-Plasma Accelerator

Recently, the possibility of LPA-produced muon beams has gained significant interest within the accelerator physics community. At BELLA, we unambiguously detected muons generated during the interaction of multi-GeV electron beams with a 4 meter-thick electron beam dump. Building on the success of that initial experiment, we conducted a second campaign to extend our diagnostic capabilities to single-muon energy measurements. To achieve this, we developed a muon telescope that operates two stacks of three silicon tracking detectors, each consisting of a single ATLAS ITkPix readout chip-based silicon detector module. The two stacks are separated by a 0.5 T permanent dipole magnet. The detector was calibrated and internally aligned through extended exposure to cosmic rays. We encased the telescope in a 10-cm lead shield to reduce the background particles. This allowed us to individually reconstruct each muon trajectory that, at a minimum, passed through all three detectors of either stack. We then determined the energy of all the muons passing through both stacks by measuring their bending angle in the magnetic field. The recorded muon energies reached up to 2.8 GeV, which, after accounting for energy losses in traversing the concrete walls, demonstrates muon production up to about 6.5 GeV at the source, consistent with the incoming electron beam energies and the Bethe-Heitler process responsible for the production of these muons.

Speaker: Davide Terzani (Lawrence Berkeley National Laboratory)

141 Muon scattering tomography with laser-plasma-accelerator-driven muon source

Laser plasma accelerators (LPAs) can generate GeV scale electron beams in ultra-compact footprints, making them ideal drivers for various secondary sources. Among these is artificial muon generation, with various groups measuring LPA-driven muons recently. Muons are unstable, heavy elementary particles, that interact mostly by scattering off nuclei as they propagate through matter. This means that they can penetrate large and/or dense objects, with the scattering angle of the emerging muon carrying information about the elemental composition of traversed material. Properties of muon beams driven by an optimised LPA will be presented, along with first simulations of industrially relevant muon scattering tomography and object reconstruction using LPA-driven muons.

Speaker: Kristjan Põder (MuRayTech GmbH)

142 Development of laser-plasma accelerators at HZDR for FEL applications

In 2022, FEL light generation driven by LPA-produced electron beams was successfully demonstrated. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR), we particularly focus on the seeded FEL configuration using the COXINEL beamline. Our ongoing efforts in the development of LPA-generated beams are concentrating on improving beam quality to increase FEL gain and enable operation at shorter wavelengths. In addition to parameters such as peak charge density, energy spread, and beam divergence, stability and reliability are essential requirements for qualifying LPAs for FEL applications.

Here, we present recent developments of the LPA injector at HZDR. These include the implementation of different injection schemes, such as density down-ramp injection and hybrid laser–particle-driven acceleration, as well as optimisation of beams generated via STII (self-truncated ionisation injection). Since the 2022 demonstration experiment, we have significantly increased the peak charge density of the LPA beams. Combined with improved stability—both shot-to-shot and day-to-day—this has enabled more precise FEL studies and allowed us to reach the high-gain regime, yet currently at UV wavelengths.

Speaker: Susanne Schöbel (Helmholtz-Zentrum Dresden-Rossendorf)

15:30 Coffee Break

A2-Working group # 2

143 Electric and magnetic fields on the surface of a dense plasma with relativistic electron flows

The electric/magnetic fields generated on the surface of a dense plasma by hot electrons are considered with relativistic fluid theory. Quasi-steady state solutions are considered with both isothermal and isentropic models and conservation laws for the electron flows in terms of the four-potential and specific enthalpy. We find analytic solutions for the electric and magnetic field profiles and compare to particle-in-cell simulations, showing good agreement. The analytic model delineates refluxing and surface confinement regimes for the hot electrons. The results should be relevant to ion acceleration and magnetic field generation.

Speaker: Alexander Thomas (university of michigan)

144 On-line optimization of a high average power laser-driven ion source using Markov Chain Monte Carlo algorithm

The evolution of high peak power laser technology especially in repetition rate and pulse-to-pulse stability, as well as the development of the suitable targetry enabled LPIAs to operate quasi-continuously, at a repetition rate of around 1 Hz [1-2]. This allowed the use of optimisation algorithms based on deep learning to improve the performance of LPIA. One of the most commonly integrated algorithms is the Bayesian, where a surrogate model is created. The model is refined by sampling the parameter space, which makes it possible to predict the performance and may help to explore the physics. This optimisation method has been demonstrated to be effective in enhancing the performance of up to 2 parameters (for example wavefront control [3-5] or spectral phase [6]) and a few hundred samples in the parameter space. Besides, it performs poorly with higher sample number and optimisation for more than a very few parameters is prohibitively time consuming.
State-of-the-art ion accelerators driven by kHz repetition rate laser system open new opportunities for optimisation processes due to the larger amount of data. The Light Energy Ion Accelerator (LEIA) beamline in ELI-ALPS is driven by the Sylos3 laser system. Pulses with 8.5 fs duration and 80 mJ energy on target accelerate protons and deuterons up to 2.5 MeV cut-off energies. The system has been demonstrated to be capable of producing low-energy ions with a kHz repetition rate, utilising a thin liquid sheet target, resulting in a laser accelerated ion beam with an average power close to 10 W [7]. The LEIA beamline is equipped with two Thomson Parabola Spectrometers (TPS), which provide real-time information about the ion beam and the acceleration performance. These properties led to the use of another optimisation algorithm, namely the Markov-Chain Monte Carlo (MCMC) method. MCMC algorithm is able to manage a substantially larger number of free parameters, performs well with large number of samples, and last but not least natively converges to the optimal parameters.
To prove the feasibility of the MCMC algorithm, we have optimised the performance of the ion accelerator with the use different liquids and thicknesses. The spectral phase of the laser pulses was optimized real-time to reach the highest proton/deuteron cut-off or bunch energy at a given target material and thickness. Additionally, due to the tunability of the MCMC model we were able to scan the parameter space simultaneously, revealing the real distribution of the appointed parameters (cut-off or bunch energy) as a function of the phase derivatives. For adequate optimisation and result, 900-1000 sample points in the parameter space were necessitated, which took 15 minutes at most cases, made it possible to find the optimal parameters for different applications just before the real experiment.

References:
[1] Lelievre et al., Phys. Plasmas 31, 093106 (2024)
[2] Streeter et al., Nat Commun 16, 1004 (2025)
[3] B. Loughran et al., HPLSE, 11, e35 (2023).
[4] Catrix, E. et al., Appl. Phys. Lett. 126, 254104 (2025)
[5] Glenn et al., Phys. Rev. Research 8, 013101 (2026)
[6] Torrance et al., HPLSE 13, e105 (2025)
[7] Osvay et al, A laser-plasma accelerator with a high average power ion beam for applications, HPLSE Conference, Chengdu, China, 2026.

Speaker: Tibor Gilinger (University of Szeged)

145 Scintillator-Based High Repetition Rate Diagnostic for Multi-Energy Proton Beam Imaging & Probing

High-repetition-rate, multi-petawatt laser systems require high-throughput diagnostics capable of capturing proton beam characteristics on a shot-to-shot basis. We present GOSSIP (Glowing On-shot Scintillator Stack for Imaging Protons), a compact, reusable, multi-layer scintillator diagnostic designed to measure spatially resolved transverse proton beam profiles across multiple energies. The diagnostic has been deployed in multiple experiments, including proton beam profiling and proton probing measurements of field dynamics at the NSF ZEUS facility. Results demonstrate the ability to resolve fine beam features and capture energy-dependent spatial structure. We will also discuss key technical challenges, including scintillator material optimization, calibration requirements, and resolution limits due to scattering. GOSSIP provides a scalable approach for real-time proton beam diagnostics in next-generation high-intensity laser experiments.

This work is funded by the U.S. Department of Energy NNSA Center of Excellence under cooperative agreement number DE-NA0004146 and by the National Science Foundation through award number 2408410. This research was conducted at the ZEUS facility which is supported by the National Science Foundation under award 2126181.

Speaker: Veronica Contreras (University of Michigan)

146 Picosecond Radiation Dynamics in Materials Using Laser Driven Sources

Ionising radiation induces ultrafast cascades of electronic and structural processes in matter that ultimately govern long-lived radiation damage. However, the connection between picosecond-scale dynamics and macroscopic outcomes remains insufficiently characterised, particularly in complex or nanostructure media and under ultra-high dose-rate conditions. We present measurements of dynamics in both nanostructured silica aerogels and liquid water using picosecond bursts of x rays and laser-accelerated protons. By combining transient photo-absorption and optical streaking diagnostics, we track the full temporal evolution of electron dynamics across previously inaccessible regimes of density and dose-rate.
These measurements establish a new framework for probing radiation-matter interactions in complex systems, linking ultrafast microscopic dynamics to emergent macroscopic damage processes. This provides new frontiers in nanodosimetry and provides critical foundations for predictive models relevant to advanced radiation technologies.

Speaker: Jonathan Kennedy (Queen's University Belfast)

147 Diagnosing near-critical-density laser plasma interaction and ion acceleration using dynamic optical probing

The interaction of high-intensity lasers with near-critical density (NCD) plasmas underpins many applications, such as the generation of ultra-high peak current ion beams. However, diagnosing NCD plasmas remains challenging due to their high density, short timescales, and small spatial structures. We address these challenges by driving ion acceleration with a high-power, long-wave infrared CO₂ laser at the Accelerator Test Facility (ATF), Brookhaven National Laboratory. The longer drive wavelength reduces the critical density and increases the spatial scale, enabling both the use of gas targets and the implementation of probing with a synchronised optical laser [1]. A recent upgrade at the ATF has enabled probing with much shorter pulse length than the drive beam, enabling dynamic intrapulse imaging. We will discuss measurements of laser channeling propagation velocity and transverse expansion in near-critical-density plasma and sheath-like ion acceleration at ionization boundaries. Our novel platform can be extended to provide new insights into a wide range of intense laser-plasma phenomena.

[1] Dover et al. Physical Review Letters 134, 025102 (2025)

Speaker: Nicholas Dover

148 Contrast enhancement results of a novel spatially-combined, pulse-stacked ultrafast fiber laser system

Ultrafast lasers with both high average and peak power are necessary to drive laser wakefield acceleration. Fiber lasers have recently demonstrated potential to meet such challenging demands, but they still run into the primary roadblock of lower temporal contrast, a key parameter for characterizing pre- and pedestal pulses which cause pre-ionization of the target gas. Second harmonic generation (SHG) remains the standard choice for significantly improving contrast due to the intensity-squared scaling of contrast enhancement, as well as bottlenecking any pedestals with unsuitable nonlinear pulse characteristics. We present results of SHG from a spatially combined, coherent pulse-stacked femtosecond laser (10 mJ, 300 fs, 1 kHz) developed by the University of Michigan. We also estimate contrast enhancement by directly comparing the SHG pulse to the fundamental pulse.

Speaker: David Feng (Lawrence Livermore National Laboratory)

A4-Working group # 4

149 A-STRA: a wakefield accelerator for high-repetition rate XFELs

A compact collinear wakefield accelerator has been developed for an X-ray free-electron laser operating at X-ray pulse repetition rates in the tens of kilohertz. The maximum achievable accelerating gradient is evaluated, with its upper limit constrained by beam breakup instability. Key fabrication techniques for the accelerator’s principal components—including wakefield generation structures, excess-power extraction couplers and diagnostics, focusing quadrupoles, and a novel undulator—are presented. Results from both laboratory and electron beam-based tests are compared with design specifications, showing strong agreement. Finally, prospective directions for future research are outlined.

Speaker: Alexander Zholents (Argonne National Laboratory)

150 Progress on a High-Gradient Booster Linac for Multi-GeV Proton Radiography at LANSCE

A high-gradient energy booster linear accelerator (linac) is under investigation to increase the proton beam energy from 800 MeV to 3-5 GeV for the Proton Radiography (pRad) facility at Los Alamos Neutron Science Center (LANSCE). The increased beam energy is expected to enhance the resolution of radiography by one order of magnitude. We are evaluating a compact and cost-effective architecture involving normal-conducting radiofrequency (NCRF) accelerating structures operating at liquid-nitrogen temperature; this linac will operate with short RF pulses at very low duty. The proposed pRad booster linac comprises an initial L-band structure for beam capture and compression, S- and C-band main linac sections, and an L-band debuncher at the end, which may be employed for reducing the energy spread of the beam, depending on pRad operation requirements. In this project, we are developing S- and C-band prototypes for testing under cryogenic conditions for evaluating their high-gradient performance. We are meanwhile evaluating beam dynamics design options for the booster linac and performing initial proton radiography simulations.

Speaker: Haoran Xu (Los Alamos National Laboratory)

151 LWFA-fed Compton Source Based on Dual-Energy Accumulator Ring with Cryocooled Nb3Sn Twin-Axis Cavities

We present a concept for a compact soft X-ray Compton source targeting the water-window spectral range (2.3–4.4 nm, 280–540 eV), based on an unconventional combination of three advanced accelerator technologies: laser-wakefield acceleration (LWFA) for top-up injection, a dual-energy accumulator ring with energy recovery, and cryocooled Nb3Sn twin-axis superconducting RF cavities.

The source concept exploits LWFA in the low-energy, high-density regime (n_e ~ 10^19–10^20 cm^-3, a_0 ~ 1–2) to deliver a sub-MeV electron bunch (~0.2 MeV) into a compact storage ring. Electrons are accelerated to ~3 MeV by twin-axis Nb3Sn cavities operating at 4K via cryocooler, then collide with stored photons in a high-finesse optical cavity to produce Compton-scattered X-rays in the water window. After the interaction, the spent beam is decelerated through the same twin-axis cavity structure, recovering most of its energy — the dual-energy accumulator ring architecture thereby supporting both acceleration and deceleration in a single compact cryomodule.

We discuss the physics and engineering of each subsystem: the optimal LWFA injection regime and the interplay between self-injection dynamics, extraction energy, and energy-recovery ratio; the Nb3Sn cavity design with low-beta first cell to accommodate sub-relativistic injection; the estimated Compton photon flux (~10^14–10^16 ph/s) and average power (~30 mW central estimate) in the water window; and the key open questions requiring simulation and experimental validation. The concept represents a qualitatively new point in the design space for compact, lab-scale, coherent-quality X-ray sources, leveraging the maturity of LWFA technology at modest laser energies (35 mJ, 35 fs) to enable a source that would otherwise require a full synchrotron facility.

Speaker: Andrei Seryi (ODU)

A5-Working group # 5

152 Analysis and mitigation of second-order effects in an asymmetric emittance exchange beamline

We present simulation results on the generation of sub-micron longitudinal beam modulations using an emittance exchange (EEX) beamline. An initial transverse modulation is produced with a transmission electron microscope (TEM) grid and mapped into the longitudinal plane through an asymmetric EEX configuration, where different dogleg bending angles are employed to reduce CSR-induced distortions. While the asymmetric configuration mitigates CSR effects, nonlinear second-order effects significantly degrade the final phase space structure. To address this, we identify the dominant second-order contributions, analyze their evolution along the beamline, and implement sextupole-based mitigation to suppress these effects. The results demonstrate longitudinal bunch train with sub-micron modulation periods and a bunching factor of 0.6 at 1 pC.

Speaker: Buse Naz Temizel Ozdemir (Northern Illinois University)

153 3D Simulation and Analysis of Coherent Synchrotron Radiation with Shielding

The accurate modeling and mitigation of coherent synchrotron radiation (CSR) represents an important challenge in the design of high-brightness beam transport systems. Widely used beam-dynamics codes typically employ a 1D line-charge approximation, reducing CSR to a longitudinal wake that is uniform across the bunch. While computationally efficient, this approach neglects transverse beam structure and becomes unreliable for beams with high transverse-longitudinal aspect ratios. Although 2D/3D CSR implementations exist, existing approaches sacrifice at least one of: a full 3D beam distribution, entry/exit wake treatment, conducting-wall shielding, or self-consistency. In this work, we present a new simulation approach that achieves fully 3D, self-consistent CSR calculation by extending the 1D framework of Mayes and Hoffstaetter (2009) to a set of transversely staggered integration lines. At each timestep, the beam distribution is represented in a co-moving frame as a weighted sum of smooth 3D shape functions, which simplifies the retardation condition while keeping the memory footprint low — enabling the natural inclusion of shielding via image charges. We will discuss the theoretical foundations of this approach and its computational characteristics relative to existing methods. The technique is currently being applied to study the boundary between 1D and 3D CSR regimes, to characterize transient and steady-state shielded wake dynamics, and to support multi-parameter optimization of shielding geometries in concert with beam profile shaping for CSR mitigation. This work is part of a larger investigation into CSR effects on beam dynamics that includes experimental analysis at the Argonne Wakefield Accelerator (AWA).

This research was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award DE-SC0024445.

Speaker: Omkar Ramachandran (Argonne National Laboratory)

154 Interactive Simulated Beam Loss Diagnostics Enabled by a Location-of-Loss Surrogate Model

In many advanced accelerator applications, average power is limited by beam loss. The rate and location of losses due to Touschek scattering and residual gas scattering can be accurately computed with knowledge of the lattice. However, these calculations are expensive: involving Monte-Carlo methods where each of the millions of samples is tracked through the machine to the location of its eventual demise. This expense has prohibited the use of loss modeling in an operational or diagnostic setting. In this talk, we introduce a new surrogate model capable of predicting the location of beam loss from its initial scattering coordinates. In experiments on our example lattice, the model achieves ~1 m accuracy at speeds two to three orders of magnitude faster than conventional tracking through the lattice. For many practitioners, the full cost of dataset generation, model training, and inference is less than that of the equivalent classical method through a combination of sharing the model across scattering processes and the sample inefficiency of Monte-Carlo techniques. This work brings loss modeling into the control room - turning a day-long computation into one that is completed in near real time and can be updated interactively with actual and proposed changes to the beam and scattering parameters.

Speaker: Christopher Pierce (xLight Inc)

155 Status and Development of tailored phase space correlation generation using transverse wigglers

There is an ongoing project to develop a framework for recently proposed arbitrary correlation generation and to theoretically and experimentally explore its applications. Currently, a transverse wiggler-based approach is considered to be the main method for realizing tailored correlations. Current developments focus on the following items: limiting factors of the transverse wiggler, a method to determine the required beamline and function-type correlations to obtain more generalized 2D correlations, and transverse wiggler optimization and feedback control. Along with these development efforts, we are also preparing the first demonstration of sawtooth correlation generation, which aims to achieve a 50-100% higher bunching factor than nominal single-sine modulation. We start by introducing the project and present the current status.

Speaker: Gwanghui Ha

156 Virtual diagnostic for phase space prediction and customization at FACET-II

Accurate characterization of Longitudinal Phase Space (LPS) is critical for the optimization and operation of high-brightness electron beams at SLAC’s FACET-II facility. However, direct measurement of LPS typically relies on invasive diagnostics, such as the X-band Transverse Deflection Cavity (XTCAV), which cannot operate simultaneously with user experiments. To bridge this gap, we present a hybrid machine learning framework for high-fidelity, non-invasive LPS prediction by pairing a Convolutional Variational Autoencoder (CVAE) with a Random Forest (RF) regressor.
​In this architecture, the CVAE is utilized to compress high-dimensional LPS images into a compact latent manifold, typically ranging from 12 to 20 dimensions depending on the specific beam configuration. A Random Forest model is then trained to map a high-dimensional set of scalar diagnostic data—comprising 200 to 800 EPICS variables—directly to this latent space. Despite high redundancy and a signal dominated by approximately six principal axes given by energy BPM (Beam Position Monitor) and BLEN (Bunch Length Monitor), the RF architecture is heuristically optimized to maintain robustness against feature dilution and control-system noise.
​The resulting model successfully reconstructs the latent manifold, enabling the rapid decoding of beam dynamics with minimal computational latency. This system has been integrated into a production-ready graphical user interface (GUI) developed in PyDM, which is currently deployed at the FACET-II beamline for real-time operator support and beam tuning. This work demonstrates the efficacy of latent space regression as a non-invasive, "virtual diagnostic" in complex accelerator environments.

Speaker: Jinseo Park (SLAC National Accelerator Laboratory)

A6-Working group # 6

157 An MeV X-ray source from Laser Wakefield Acceleration based betatron radiation

Laser-driven plasma X-ray sources are attractive for High Energy Density Science, particularly for diagnosing Inertial Confinement Fusion implosions and resolving the influence of hydrodynamic instabilities such as Rayleigh-Taylor growth. For these applications, an effective source must combine high spatial resolution (< 50 um) with photon energies reaching several hundred keV, sufficient to probe within the gold hohlraum. Betatron radiation generated in Laser-Wakefield Acceleration is especially compelling because it’s resolution is typically 10s of microns, depending on laser and plasma conditions. In this study, we evaluate the spectral extent and spatial resolution of betatron emission produced in a plasma-waveguide enhanced LWFA configuration, parameters that have not previously been characterized for this regime. We will present measurements obtained during an August 2025 campaign at the ELBA end station of ELI Beamlines using the HAPLS laser system (800 nm, 30 fs, 15 J, .2 Hz), including the resulting X-ray flux, critical energy, and source size. These measurements also offer new experimental insight into wakefield behavior under this enhancement scheme for LWFA, particularly into electron beam trajectories reflected in the observed betatron source size. Previous studies have shown that limited flux and substantial shot-to-shot variability have hindered the broader use of betatron X-rays compared with more established platforms such as X-ray tubes and synchrotron facilities. By exploring the role of a plasma waveguide on LWFA X-ray source generation, we seek to clarify how deliberate shaping of electron beam properties within a laser wakefield can control X-ray source performance and determine its suitability for targeted applications.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, supported by the LDRD program under tracking code 25-ERD-010 and the Foster-Brown Fellowship. LLNL-ABS-2013664

Speaker: Isabella Pagano (Lawrence Livermore National Laboratory)

158 Direct laser acceleration and betatron radiation in arbitrary-velocity wakefields

Electrons accelerated in the plasma wake of a high-intensity laser pulse can reach higher energies by interacting with a second, delayed pulse. The total energy gain depends on the phase velocity of the wake and the phase and group velocities of the pulses. With conventional pulses, these velocities are set by the plasma density, which limits the maximum energy gain. Here, we show that flying-focus pulses can enhance the energy gain in synergistic laser wakefield and direct laser acceleration by enabling control of the wake and pulse velocities independent of plasma density. The higher electron energies, in turn, result in brighter and more energetic betatron x-rays. Calculations demonstrate that higher electron energies and enhanced x-ray emission are achievable with experimentally realizable flying-focus pulses on 100-TW-class laser systems.

This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number(s) DE-NA0004144, and the US Department of Energy, Office of Science, under Award Number DE-SC0021057.

Speaker: Lavonne Mack

159 Shallow-angle and superradiant inverse Compton scattering

Compact Inverse Compton Scattering (ICS) sources offer tunable radiation in the X-ray spectral range essential for a wide range of scientific and technological applications. Unfortunately, their utility is limited by low brightness compared to large-scale facilities, resulting from the small scattering cross-section and large emission opening angle. Here, we present two synergistic strategies to overcome this limitation. First, a shallow-angle scattering geometry enhances brightness with spectral control independent of electron beam energy. Recent experiments at the UCLA Pegasus laboratory, including the demonstration of shallow-angle ICS and the observation of the relativistic Brewster effect will be discussed. Second, the superradiant regime is explored, promising an orders-of-magnitude increase in brightness by spatially structuring the electron beam at the radiation wavelength scale. Building on the flexibility of spectral tuning by crossing angle, we will show that superradiant ICS can be achieved via inverse free electron laser bunching. This approach will be exploited in our upcoming experiment at the Accelerator Test Facility at Brookhaven National Laboratory.

Speaker: Brian Schaap (UCLA)

160 Wavefront shaping of terahertz radiation using two-color flying-focus pulses

Properly phased two-color laser pulses drive photoionization currents that emit broadband THz radiation. With conventional two-color pulses, the ionization front travels at a nearly constant superluminal velocity, generating THz radiation with conical wavefronts at a Cherenkov-like angle. Here we show that the dynamic intensity peak of a two-color ultrashort flying-focus pulse can be used to control the shape of the THz wavefronts. Simulations demonstrate that non-uniform motion of the intensity peak and the ionization front it drives result in a time-dependent emission angle that determines the wavefront shape. A decelerating intensity peak, in particular, enables the generation of THz radiation with parabolic phase fronts that are well suited for collection and focusing.

Speaker: Amanda Elliott (Laboratory for Laser Energetics)

161 Coherent Smith-Purcell radiation from plasma-accelerated electrons: a synchronized strong-field terahertz radiation source

Undulating surface currents that charged particles induce in a metal grating as they pass over its facets at close range emit broadband Smith-Purcell radiation (SPR) into an angle-encoded fan of wavelengths 𝜆(𝜃), where the angle 𝜃 is measured from the particle propagation direction [1, 2]. If the length l = c𝜏 of a charged particle bunch of duration 𝜏 is shorter than the grating period d, then SPR at 𝜆 > d becomes coherent, and the energy of the coherent portion of the radiated pulse is proportional to N^2, where N is the number of particles in the bunch. Thus, few-femtosecond (c𝜏 ≈ few micrometers) electron bunches from laser-wakefield accelerators (LWFAs) can generate strong coherent SPR (CSPR) at much shorter wavelengths than was possible with few-picosecond (c𝜏 ≈ few millimeters) bunches typical of RF accelerators [2]. We experimentally confirmed that SPR remains strongly coherent down to the shortest THz wavelengths (𝜆 ≈ 10 µm) when generated by few-fs LWFA electron bunches [3], as described in separate workshop contributions.

Here, we address the question of whether the radiated CSPR "fan" can be tailored into strong-field (≳ GV/m) pulses that are useful for ultrafast nonlinear THz spectroscopy in applications such as nonlinear phononics, solid-state high-order harmonic generation, and ultrafast magnetic switching. Through simulations, we show that it is possible to remove the inherent spatial and angular chirp of a selected angular cone of the THz CSPR fan, compress the remaining longitudinally-chirped waveform to sub-ps duration, and focus the compressed pulses to field strengths of several GV/m using standard commercially-available optical components from chirped-pulse amplification (CPA) technology. The unique advantage of LWFA-driven CSPR over existing strong-field THz sources based on optical rectification of sub-ps infrared laser pulses in 𝜒(2) crystals [4] is the perfect synchronization of the CSPR pulses with the fs e-bunches that generated them. Thus, they are also perfectly synchronized with secondary betatron or inverse-Compton-scattered hard X-ray pulses of fs duration that the e-bunches generate. This opens the possibility for jitter-free probing of THz-driven structural dynamics via fs X-ray diffraction or fs X-ray absorption spectroscopy. The principal advantages of LWFA-driven CSPR over RF-accelerator-driven THz sources [5] are its compactness, low cost, mobility, and configurability. Any existing LWFA laboratory can home-build the CSPR generation, detection, de-chirping, and focusing systems presented here at low marginal cost. Thus, LWFA-driven CSPR offers unique capabilities for ultrafast strong-field THz spectroscopy that complement existing laser-based and RF-accelerator-based THz sources.

[1] S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953).
[2] G. Doucas, Smith-Purcell Radiation: Basic Theory and Applications (Oxford U. Press, 2025).
[3] R. Rudzinsky et al., Optica 13 (5), 810-821 (2026).
[4] C. Vicario et al., Phys. Rev. Lett. 112, 213901 (2014); G. Toth et al., Light Sci. Appl. 12, 256 (2023).
[5] B. Green et al., Sci. Rep. 6, 22256 (2016); M. Helm et al., Eur. J. Phys. Plus 138, 158 (2023).

Speaker: Mike Downer (The University of Texas at Austin)

162 Results from the FACET-II E320 Strong-field QED program

The E-320 experiment at SLAC FACET-II aims to investigate Quantum Electrodynamics (QED) in the strong-field regime.
By colliding 10 GeV, high-quality electron beams with 10 TW NIR laser pulses it is aspired to probe the QED critical (Schwinger) intensity of 10E29 Wcm-2 in the electron rest frame. In this regime, characterized by X = E/Ecr>1, quantum corrections to classical synchrotron radiation become important and the probability for electron-positron pair production is no longer exponentially suppressed. Due to comparatively high stability and low energy spread in the FACET-II electron beam, E320 is able to contribute precision measurements of the emerging processes.
The experiment E-320 is to studying the transition from the perturbative (a0^2<<1) to the non-perturbative regime (a0^2>>1), characterized by the intensity parameter a0, while quantum effects are relevant (i.e., X ~ 0.1 ).
We report on the measurements of the red shift of the Compton edges and the transition to a quasi-continuous spectrum, as well
as current and future efforts towards the measurement of the Nonlinear-Breit-Wheeler process.

Speaker: Alexander Knetsch (SLAC National Accelerator Laboratory)

Banq

Friday 31 July

08:15 Breakfast

Invited Talks

163 Progress in THz acceleration

Review of recent progress in THz-based acceleration

Speaker: Prof. Franz Kaertner (DESY)

164 Dephasingless laser wakefield acceleration of electrons using a flying focus

Laser wakefield acceleration (LWFA) is a highly promising route to realizing compact particle accelerators and radiation sources, utilizing electric fields >100 GV/m to produce multi-GeV electron beams with percent-scale energy spread and sub-mrad divergence. Until now, the maximum producible electron energy has been limited by dephasing, where electrons outrun the accelerating phase of the wakefield and stop gaining energy. Current state-of-the-art accelerators achieve 10 GeV energies by using a reduced plasma electron density to increase the group velocity of the drive pulse. But this has several drawbacks, including a reduction of the accelerating field. Using a flying focus—a technique which allows the velocity of the peak laser intensity to be precisely controlled—we show that dephasing can be eliminated by driving a wakefield at the vacuum speed of light. Scaling this approach could enable substantially higher energy electrons to be produced while maintaining >100 GV/m accelerating gradients in a compact accelerator with small-f/# optics. Using near-future 20 PW laser systems, 100 GeV electron energies are predicted. In this talk, I will present recent experimental results demonstrating electron acceleration over multiple dephasing lengths and discuss some of the challenges involved in scaling DLWFA to the multi-GeV regime.

Speaker: Charles Arrowsmith (University of Rochester Laboratory for Laser Energetics)

165 High-dimensional phase space reconstruction using generative modeling of beam distributions

Advanced accelerator concepts rely on the precise measurement and control of the beam distribution. However, conventional methods used to characterize precise features of the beam distribution in six-dimensional phase space require many measurements taken over tens of hours of beam time. In recent years, generative phase space reconstruction (GPSR) has been shown to significantly reduce the number of measurements needed to reconstruct the beam distribution in four-, five-, and six-dimensional phase space by using a generative model of the beam combined with differentiable beam dynamics simulations. In this talk, we present an overview of the GPSR method, including its implementation at the Argonne Wakefield Accelerator and other facilities. Furthermore, we show recent developments in GPSR that enable its use in real time for online tuning of beam distributions in advanced accelerator applications.

Speaker: Juan Pablo Gonzalez-Aguilera (SLAC National Accelerator Laboratory)

10:15 Coffee Break

Student Prizes

UCLA lab tours (optional)