NEFERTARI final workshop - Padova 25-27 March 2026

25 Mar 2026, 07:00 → 27 Mar 2026, 17:00 Europe/Rome

Auditorium / Sala Blu (Orto Botanico Università di Padova / Area della Ricerca CNR Padova)

 

Final workshop of the NEFERTARI project (New Equipment for Fusion Experimental Research & Technological Advancements with Rfx Infrastructure)

 

The aim of the workshop is to provide a discussion forum covering the scientific and technological objectives achieved with the NRRP-IR project NEFERTARI.

NEFERTARI project website: <https://www.istp.cnr.it/nefertari/>

 

Participation in the event is limited to the staff of the entities involved in the project and to experts invited by the Scientific Committee 

Hotel-list.pdf

Locations-Padova-downtown.pdf

NEFERTARI-timetable.pdf

Wednesday 25 March

08:30 → 09:00 Accoglienza e registrazione

09:00 → 10:30 # Sessione istituzionale: l'impatto del PNRR negli EPR e Università #

Convener: Olga DE PASCALE (CNR ISTP)

09:00 → 09:05 Benvenuto dell'Università degli Studi di Padova

Speaker: Prof. Paolo BETTINI

09:05 → 09:15 Intervento del Ministero dell'Università e della Ricerca

Speaker: Dr Michele MAZZOLA (Ministero dell'Università e della Ricerca)

09:15 → 09:25 Intervento del Direttore del CNR-DSFTM e vicepresidente del Consorzio RFX

Speaker: Dr Stefano FABRIS (CNR-DSFTM)

09:25 → 09:45 The PNRR-IR NEFERTARI project: a network of Research Infrastructures for Magnetic Confinement Fusion Research

In the framework of the Italian National Recovery and Resilience Plan (NRRP), funded by the European Union NextGenerationEU plan, the project named “New Equipment for Fusion Experimental Research and Technological Advancements with the RFX Infrastructure” (NEFERTARI) has been awarded of funding by the Italian Ministry of University and Research (MUR), with the main aim of strengthening the research infrastructures and more specifically in fusion energy field [1].

The scientific and technological objectives of the project are mainly the enhancement of a large set of experimental plants and diagnostic systems for the RFX-mod2 fusion experiment, based in Padova (Italy), capable of operating both in Reversed Field Pinch and Tokamak configuration, and the reinforcement of an integrated network of laboratories (located in different Italian sites, Bari, Milano, Napoli) with specific competences on plasma wall interaction, diagnostics for imaging of soft X-rays and neutrons, optical plasma diagnostics, High Voltage insulation, Remote Handling Systems.

The project has been shared among 3 public research institutions (CNR, University of Napoli, University of Padova), with contribution of Consorzio RFX as third party, and involved a team of 50 Full Time Equivalent per year, a total budget of 18 M€, with a duration of 3,5 years (2022-2026).

This contribution presents an overview of the project results, highlighting challenges and strengths from scientific, financial and managerial perspective, and provides prospects for the exploitation of this Research Infrastructure in the international context of fusion science and technology development for the forthcoming years, after the completion NEFERTARI project.

[1] <Avviso pubblico per la presentazione di proposte progettuali per “Rafforzamento e creazione di Infrastrutture di Ricerca” da finanziare nell’ambito del PNRR> Missione 4, “Istruzione e Ricerca” - Componente 2, “Dalla ricerca all’impresa” - Linea di investimento 3.1, “Fondo per la realizzazione di un sistema integrato di infrastrutture di ricerca e innovazione”, finanziato dall’Unione europea – NextGenerationEU; MUR Avviso n.3264, 28/12/2021 https://www.mur.gov.it/it/atti-e-normativa/avviso-n-3264-del-28-12-2021

Speakers: Lionello MARRELLI (Consorzio RFX), Monica SPOLAORE, Simone PERUZZO (Consorzio RFX)

20260325_Nefertari-finalWS_MSpolaore_v05.pdf

Nefertari_FinalWorkshop_day1_Peruzzo.pdf

Nefertari_FinalWorkshop_day1_Peruzzo.pptx

09:45 → 10:30 Tavola rotonda: l'impatto del PNRR nei dipartimenti universitari

moderatore: Piergiorgio Sonato

Speakers: Prof. Alberto TREVISANI (DTG, Università degli Studi di Padova), Prof. Fabio VILLONE (DIETI, Università degli Studi di Napoli Federico II), Prof. Fabrizio DUGHIERO (DII, Università degli Studi di Padova), Prof. Flavio SENO (DFA, Università degli Studi di Padova), Prof. Nicola BIANCO (DII, Università degli Studi di Napoli Federico II), Prof. Piergiorgio SONATO (Consorzio RFX)

10:30 → 10:45 coffee break

10:45 → 13:15 # Le IR per la fusione potenziate con il PNRR e i potenziali stakeholders #

Conveners: Nicola VIANELLO (Consorzio RFX), Roberto PASQUALOTTO (Consorzio RFX)

10:45 → 11:15 keynote speech EUROfusion

Speaker: Dr Gianfranco FEDERICI (EUROfusion Consortium)

GFEDERICI@Padova_fin2.pdf

GFEDERICI@Padova_fin2.pptx

11:15 → 11:45 keynote speech ENI Magnetic Fusion Initiatives

Speaker: Dr Francesca FERRAZZA (Eni SpA)

11:45 → 12:10 The RFX-mod2 experiment

RFX-mod2 is an evolution of the Reversed Field eXperiment (RFX), succeeding the RFX-mod configuration. Unlike the original RFX, which was a thick-shell device, RFX-mod and RFX-mod2 feature a thin copper shell and a network of 48 × 4 independently fed saddle coils.

The plasma-shell distance and the high resistivity of the Inconel vacuum vessel were identified as limiting factors for RFX-mod. Consequently, in RFX-mod2, the vacuum vessel has been removed and the other vessel components have been modified, thanks to EU Regional Development Funds (ROP-ERDF), to ensure vacuum tightness while reducing the shell-to-plasma radius ratio b/a from 1.11 to 1.04.

Supported by NEFERTARI funding, RFX-mod2 is equipped with improved core and edge diagnostic systems aimed at exploring new regimes (such as the fast-rotating Tearing Modes observed only at very low current in RFX-mod) and investigating remaining open issues in RFP research.

Furthermore, the flexibility of its control systems, magnets, power supplies, and new diagnostics will allow RFX-mod2 to characterize various magnetic configurations, including Ohmic tokamaks with very-low-q (q(a)<2), shaped configurations, ultra-low-q (q(a)<<1) regimes. This will facilitate the study of fundamental physics phenomena (e.g., the effects of 3D fields on MHD dynamics, edge turbulence, and transport barrier physics) and the exploration of demanding scenarios such as disruptions, runaway electrons, and sideway forces.

Speaker: Lionello MARRELLI (Consorzio RFX)

RFX-mod2-experiment_v5.pdf

RFX-mod2-experiment_v5.pptx

12:10 → 12:35 The BiGyM Project: Status and Perspectives

GyM [1] is a linear plasma device (LPD) operating at Istituto per la Scienza e Tecnologia dei Plasmi, CNR, Milan, with the aim of studying the plasma-material interaction (PMI) for magnetic confinement nuclear fusion applications. GyM is part of the portfolio of the EUROfusion facilities and one of the LPDs of the EU Contracting Party involved in the IEA Technology Collaboration Programme on Plasma-Wall Interaction.
This contribution reviews the upgrade of GyM, named “BiGyM”, currently underway as part of the NEFERTARI project [2] funded by Next Generation EU, which is due to conclude at the end of April 2026. The aim of the upgrade is to extend the accessible parameter space from plasma densities of 10$^{16}$–10$^{17}$ m$^{-3}$ and ion fluxes of 10$^{20}$–10$^{21}$ m$^{-2}$s$^{-1}$, suitable for reproducing ion and charge-exchange neutral fluxes impinging on the main chamber wall of tokamaks, such as ITER, towards 10$^{18}$–10$^{19}$ m$^{-3}$ and 10$^{22}$–10$^{23}$ m$^{-2}$s$^{-1}$, which are more representative of divertor conditions. This is being achieved by installing two helicon plasma sources, each delivering 10 kW of power via 13.56 MHz RF birdcage antennas [3]. In addition, a new sample exposure system has been developed to reproduce the operating conditions of ITER divertor plasma-facing components by heating the samples up to 1500 K and applying a negative bias voltage down to –300 V, thereby enabling precise control over the energy of the incident ions. Finally, GyM’s PMI diagnostic capabilities are also being enhanced through the implementation of a picosecond laser-induced breakdown spectroscopy (ps-LIBS) for in situ characterization of material composition changes and hydrogen isotope retention. Procurement was completed in February 2026, and the upgrade phase has recently begun. The GyM vessel has been disassembled and the layout rearranged to accommodate the new sectors for the two helicon birdcage antennas. First vacuum tests have been successfully completed, and the BiGyM magnetic configuration has also been implemented. The new pumping system is now being achieved. First plasma is expected by June, with PMI experiments planned later in 2026.

[1] A. Uccello, et al., Front. Phys. 11, 1108175 (2023)
[2] L. Marrelli, et al., manuscript submitted to Nucl. Fusion
[3] Ph. Guittienne, et al., Plasma Sources Sci. Technol. 30, 075023 (2021)

Speaker: Andrea UCCELLO (Consiglio Nazionale delle Ricerche, Istituto per la Scienza e Tecnologia dei Plasmi (CNR-ISTP))

Uccello_NEFERTARI_workshop_v1.pptx

12:35 → 13:15 Tavola rotonda: Prospettive di ricerca nei laboratori per ricerche sulla fusione potenziati nell'ambito del progetto PNRR-IR NEFERTARI

moderatori:
Roberto Pasqualotto (CNR-ISTP & Consorzio RFX)
Nicola Vianello (CNR-ISTP & Consorzio RFX)

Speakers: Dr Alessandra CANTON (Consorzio RFX), Prof. Alfredo PIRONTI (Università degli Studi di Napoli Federico II), Francesca FERRAZZA (Eni SpA), Gianfranco FEDERICI (EUROfusion Consortium), Dr Olga DE PASCALE (CNR ISTP), Prof. Paolo BETTINI (Università degli Studi di Padova, CRF)

13:15 → 14:15 pausa pranzo

14:15 → 16:20 # Overview delle principali linee di ricerca sviluppate nel progetto NEFERTARI #: part 1

Conveners: Lionello MARRELLI (Consorzio RFX), Monica SPOLAORE

14:15 → 14:30 From RFX-mod to RFX-mod2: revamping of the Technological Plants within the NEFERTARI Project

The RFX experiment has been in operation since 1991. A first upgrade, leading to the RFX-mod configuration, was completed in 2004. This upgrade enabled significant improvements in the understanding of fundamental plasma physics and the development of technological solutions, particularly in the field of active MHD control. These systems proved successful in mitigating the effects of plasma modes and in investigating the properties of the Reversed Field Pinch (RFP) configuration up to a plasma current of 2 MA, the highest value ever achieved in an RFP experiment.
RFX-mod operated for more than ten years and, in 2016, entered a new upgrade phase aimed at overcoming the limitations encountered during its operation. This upgrade led to the development of RFX-mod2. The main upgrades include a new vacuum vessel, a new boundary structure surrounding the plasma, and a redesigned layout of magnetic sensors. These modifications are expected to improve the plasma start-up phase, while the slight increase in plasma radius and the reduction of the distance between the plasma and the stabilizing wall are expected to enhance equilibrium control, reduce error fields, decrease the amplitude of tearing modes, and improve plasma transport.
Thanks to funding obtained within the framework of the NEFERTARI project under the Italian National Recovery and Resilience Plan (PNRR), a major revamping of key RFX-mod2 technological systems has been carried out.
In particular, the acquisition of an absolute laser tracker, a high-precision 3D metrology system, enabled the accurate assembly of the new machine boundary of RFX-mod2. This includes the installation and alignment of the graphite tiles composing the first wall, the conductive stabilizing shell with its fixing rings, and the vacuum vessel. The same system will also be employed for the installation and alignment of the new diagnostics developed within the NEFERTARI project.
Additional major activities comprised the refurbishment of the vacuum pumping system and of its control system, which now also integrates the gas injection control [1]. Furthermore, the boronization system has been upgraded in order to comply with the updated ATEX regulations.
Particular attention has been devoted to first-wall conditioning techniques, namely Glow Discharge Cleaning (GDC) [2] and Pulse Discharge Cleaning (PDC).
For GDC, a new system of movable electrodes has been designed, manufactured, and tested. This system will complement the existing mobile electrode system, which has also been modified with respect to the original design and will operate only in continuous current without the RF power. In addition, a new control system for the GDC plant has been developed and tested.
Due to the presence of gaps in all conducting structures (the copper shell and the vacuum vessel), high-temperature baking with induced currents will not be possible in RFX-mod2. Therefore, wall conditioning will rely on Pulse Discharge Cleaning. The PDC system, originally built in 2000, had not been modernized or commissioned and has therefore required significant upgrades.
[1] M. Zausa et al., Upgrade and Optimization of the Vacuum System for RFX-mod2 within the NEFERTARI Project, in this book of abstract
[2] M. Fadone et al., Glow Discharge cleaning efficiency analyses in view of RFX-mod2 operation, in this book of abstract

Speaker: Luca GRANDO (Consiglio Nazionale delle Ricerche - Istituto per la Scienza e Tecnologia dei Plasmi c/o Consorzio RFX Corso Stati Uniti, 4 35127 Padova PD - ITALY)

Nefertari_FinalWorkshop_WP1_final.pdf

Nefertari_FinalWorkshop_WP1_final.pptx

14:30 → 14:45 FARHA-ONE: Remote Handling Test and Training facility for RFX-mod 2

Remote Maintenance is essential for ensuring the safe, reliable, and long‑term operation of fusion machines, including devices such as RFX-mod2, DTT, and ITER.
RFX was equipped with a state-of-the-art manipulator for maintenance of internal tiles without disassembling the whole machine. Thanks to NEFERTARI and in collaboration with University of Napoli Federico II and University of Padova, RFX-mod2 will be equipped with a significantly upgraded manipulator (ROMAN), complemented with a mock-up facility for test and training (FarHa-One). The aim is not only to ensure maintenance, but also to investigate advanced strategies for remote handling (RH) of in vessel components and a proper Virtual Reality Simulator improving the perception and awareness of the environment for the robots and the operators who must operate without the aid of exteroceptive sensors and must therefore base decisions on the system digital twin. The high accuracy digital twin, used for operator training and task simulation, replicates in real-time Roman, by including joint and link flexibility using an advanced modelling approach. The Remote Handling facility FarHa-One will enable the possibility to plan and test RH tasks and procedures and train operators offline without the need to access the real equipment. The facility will enable the integration of different robotic systems to validate multiple maintenance and inspection solutions. The facility will also support the validation of maintenance procedures on the real machine, covering the full operational workflow, from installation and calibration to inspection and tile removal inside the machine.

Speaker: Giuseppe DI GIRONIMO (Università degli Studi di Napoli Federico II)

Nefertari_FinalWorkshop_DIGIRONIMO.pdf

WP1_A3_RH_ABSTRACT_DIGIRONIMO-GIUSEPPE.pdf

14:45 → 15:00 Revamping of the Remote Handling System for RFX-mod2 and design of a test facility within the NEFERTARI Project

The Remote Handling System (RHS) of the RFX experiment has been in operation since 1991. Subsequently, following major upgrades to the toroidal assembly and power supply systems, RFX-mod began operation in 2004, while the original RHS remained essentially unchanged.
Thanks to funding obtained within the framework of the NEFERTARI project under the Italian National Recovery and Resilience Plan (PNRR), a new project was launched to design and construct an upgraded Remote Handling System intended to support the experimental activities of RFX-mod2.
The first step of the work package focused on a detailed analysis of the previous Remote Handling System to identify its strengths and limitations. Based on this analysis, a new kinematic architecture was developed in collaboration with the Naples research unit under the direction of Prof. Di Gironimo. The first section of the arm is largely similar to the previous design, while a novel elbow joint was introduced to address issues related to stiffness and backlash. In addition, the transporter arm was also redesigned and updated.
The second phase of the work focused on defining an appropriate control architecture for the motors of the new remote handling system. In particular, a simple Human–Machine Interface (HMI) was developed using a touchscreen display directly connected to the machine controller.
To support the development of control architecture, a dedicated test facility was designed and several electrical motors and devices were acquired. In particular, a robotic arm controlled by the same control system as the new remote handling system was installed, together with a precision measurement device used to evaluate positioning accuracy and to calibrate the kinematics of both the robotic arm and the remote handling system.

Speaker: Giovanni BOSCHETTI (Dipartimento di Ingegneria Industriale (DII) - Università di Padova)

Giovanni Boschetti - Revamping of the Remote Handling System.pptx

15:00 → 15:30 Electromagnetic measurements and feedback control in RFX-mod2

Electrical and magnetic measurements play a fundamental role in magnetically confined fusion research, including devices such as RFX-mod2, DTT, and ITER, as well as in plasma-based systems and accelerator facilities such as SPIDER and MITICA. The magnetic and electrical diagnostics serve a dual role: they provide the real-time signals necessary for plasma control and machine protection, while simultaneously forming the primary dataset for post-shot physics analysis and most import for plasma equilibrium reconstruction, which is fundamental for all subsequent analysis.
Modern fusion devices rely on highly sophisticated plasma control architectures. A large number of coordinated controllers must operate simultaneously to shape, stabilize, and sustain the desired plasma scenario, in accordance with both experimental objectives and operational constraints. The effectiveness of these control strategies depends directly on the quality, accuracy, bandwidth, and reliability of real-time diagnostic measurements. Fast and reliable measurements are indispensable to detect off-normal events, mitigate instabilities, and safeguard both the plasma-facing components and the overall machine.
Funded through the PNRR (Piano Nazionale di Ripresa e Resilienza - National Recovery and Resilience Plan), NEFERTARI (New Equipment for Fusion Experimental Research and Technological Advancements with RFX Infrastructure) is a coordinated €18M investment program aimed at modernizing the Italian fusion research infrastructure centered on RFX-mod2. Representing a structural investment in scientific capacity, technological innovation, and human capital, NEFERTARI’s goal is to enhance diagnostic capabilities and reinforce a national network of advanced fusion laboratories. The program is organized into nine dedicated Work Packages (WPs) addressing complementary technological areas.
Work Package 2 (WP2), with an allocated budget of €2.5M for hardware and personnel, plays a central role in enhancing the experimental performance of RFX-mod2. It is dedicated to the development, installation, and integration of an advanced system for electromagnetic measurements and real-time plasma feedback control, addressing one of the key challenges in magnetically confined fusion devices: the stabilization and control of magnetohydrodynamic (MHD) instabilities. The WP's achievements are structured across three main lines:
1. Hardware Design and Signal Acquisition
The new front-end boards for the conditioning and acquisition of the signal from 1424 magnetic sensors to control the plasma and protect the machine has been designed, procured and tested. The system is based on flexible ADC architecture, providing a purely numerical integration of signals. The system simultaneously provides high-resolution DAQ for physical studies and a limited bandwidth low latency real time data stream for plasma control system. The new in air multi pair shielded cables to connect the in-vessel magnetic sensors to the acquisition boards have been procured. Additionally, the multimedia and IT materials for the new Control Room have been purchased. To ensure precise execution, a specific service contract with TF_Automazioni provided qualified personnel to support Consorzio RFX technicians during the assembly of the machine's electromagnetic sensors.
2. Machine Protection and Control Algorithms
Leveraging the CREATE-L model, a control-oriented electromagnetic model of RFX-mod2 was developed. This facilitated the creation of advanced, model-based algorithms for magnetic control and fault detection, combining physics-informed and data-driven approaches. These algorithms aim to improve stability control, increase accuracy in magnetic field regulation, and extend the operational envelope of the device. Furthermore, adaptive fault-detection strategies were developed to automatically recognize and classify abnormal conditions in real time, determining optimal corrective actions without requiring manual reconfiguration for different plasma scenarios.
3. In-House EMC Pre-Compliance Laboratory
A pre-compliance Electromagnetic Compatibility (EMC) laboratory, featuring a fully instrumented anechoic chamber, has been realized. Compliant with EMC testing standards, this facility enables radiated and conducted emission measurements, magnetic sensor calibration, and material characterization under harsh environmental conditions (strong RF/microwave, magnetic, and electrical fields). This in-house capability is a strategic asset for the rapid verification and iterative design of diagnostic electronics. By proactively assessing immunity to the severe electromagnetic noise inherent in fusion environments, the lab minimizes integration delays, reduces operational downtime, and prevents critical failures once systems are installed on the device.

Speakers: Alfredo PIRONTI (Università degli Studi di Napoli Federico II), Matteo BROMBIN (Consorzio RFX)

Electromagnetic measurements and feedback control in RFX_mod2_Part II.pdf

Electromagnetic measurements and feedback control in RFX-mod2 – Part I.pdf

15:30 → 15:50 WP- 3 Innovative diagnostics for edge fusion plasmas

Understanding edge plasma dynamics is fundamental for the success of magnetic confinement fusion, as it dictates the global energy confinement and the feasibility of first-wall materials. However, characterizing this region requires diagnostics with simultaneous high spatial and temporal resolution across diverse magnetic configurations.
Here we report on the development and implementation under the NEFERTARI project of a suite of innovative diagnostic systems for the RFX-mod2 experiment, designed to operate in reversed-field pinch as well as in tokamak equilibria.
Our approach integrates a fast reciprocating manipulator (FarM) with complex electrostatic and magnetic arrays, enabling deep-edge sampling while avoiding thermal degradation. To capture the multi-scale nature of plasma turbulence, we deployed ultra-high-frequency magnetic probes and a distributed network of over 500 in-vessel sensors, including Langmuir, ball-pen, and Mach probes. This setup is complemented by an ultrafast four-unit reflectometric system for real-time position control and density profiling, alongside advanced spectroscopic tools: a seven-camera light impurity tomography (LIT) system and a 2D-polychromator for tangential edge imaging.
Together, these systems provide a comprehensive characterization of electron temperature, density, and plasma flow, as well as the 3D interaction between particle sources and magnetic topologies.
By bridging the gap between small-scale instability detection and global plasma control, these diagnostics offer a robust framework for investigating transport phenomena in shaped and circular plasmas. These advancements are critical for optimizing the boundary conditions of future fusion reactors and validating complex magnetohydrodynamic models in non-axisymmetric configurations.

Speaker: Matteo ZUIN (ISTP-CNR and Consorzio RFX)

Nefertari_FinalWorkshop_Zuin_WP3.pdf

15:50 → 16:20 WP-4: Enhancement of RFX-mod2 main plasma diagnostics

The Reversed Field eXperiment (RFX)-mod2 device, the upgraded version of RFX-mod, is entering its operational phase with significantly enhanced diagnostic capabilities developed within the NEFERTARI (New Equipment for Fusion Experimental Research & Technological Advancements with RFX Infrastructure) project. Work Package 4 (WP-4) focuses on strengthening the main plasma diagnostics to enhance the capability to characterize performance in multiple magnetic configurations, including both Reversed Field Pinch (RFP) and tokamak regimes. The upgrade targets key parameters, including electron (Te) and ion temperature (Ti), through harmonized improvements of Thomson Scattering (TS), Soft X-Ray (SXR), bolometry and Neutral Particle Analyser (NPA).
A major effort has been devoted to the enhancement of the TS system that has been equipped with a second Nd:YAG pulsed laser capable of operating in single-shot or burst mode (0.3–3 kHz). It delivers up to 10 pulses per burst (5 at 0.3 kHz), each with an energy of 4.11 ± 0.04 J, thereby empowering temporal resolution and signal-to-noise ratio. The integration with the existing 100 Hz source required a quasi-coaxial alignment over distances exceeding 15 m. A dedicated campaign ensured that both lasers probe the same scattering volumes along the internal machine diameter. The TS diagnostic has also been upgraded with a modernized acquisition chain based on new digitizers (12-bit at 5 GS/s and 16-bit at 125 MS/s), together with a dedicated manipulator enabling efficient and reliable beam dump maintenance. Furthermore, it provides potential retro-reflection configurations to enhance the scattered signal, particularly beneficial for the tokamak configuration of RFX-mod2, typically operated at low density.
In parallel, the Soft X-Ray (SXR) tomography system has been strengthened through the realization of three new heads operating under ultra-high vacuum. Each includes three photodiode arrays viewing the plasma along defined lines of sight through pinholes and beryllium filters of different thickness. This configuration selects the SXR spectral range while suppressing UV and visible radiation. The geometry of pinholes and detectors has been optimized to maximize plasma coverage, allowing simultaneous measurements of SXR emissivity and Te profiles. Low-noise amplifiers have been procured and tested as well as photodiodes have been comparatively characterized using a calibrated X-ray source exploiting silver anode emission. In addition, a new 128-channel acquisition system operating at 1 MS/s has been designed and assessed.
The bolometric diagnostic has also been upgraded through improvements of the amplification and acquisition hardware, including validation of signal integration within the existing framework.
A Compact Neutral Particle Analyzer (CNPA) was initially proposed to complement the Ti measurements provided by the Diagnostic Neutral Beam Injector improved within WP-5. However, due to the Russian embargo, its procurement was not possible. Therefore, an upgrade of the existing NPA system has been implemented, extending the measurable energy range by a factor of 1.3 (up to 26 keV) and increasing the temporal resolution up to 50 kHz.
Overall, WP-4 has successfully progressed from design and procurement to installation, alignment and commissioning. The upgraded diagnostics will significantly enhance the capacity of RFX-mod2 to measure fundamental parameters, opening new opportunities for advanced studies of plasma phenomena.

Speakers: Paolo FRANZ (Consorzio RFX), Ruggero MILAZZO (ISTP-CNR)

20260324_poster_sxr_franz.pdf

Milazzo_Nefertari_Final_Workshop_WP4.pptx

16:20 → 16:40 coffee break

16:40 → 18:00 # Overview delle principali linee di ricerca sviluppate nel progetto NEFERTARI #: part 2

Conveners: Lionello MARRELLI (Consorzio RFX), Monica SPOLAORE

16:40 → 17:00 NEFERTARI WP5: a diagnostic neutral beam injector and spectroscopic diagnostics for RFX-mod2 core measurements

The ongoing upgrade of RFX-mod to RFX-mod2, thanks to a better stabilization of edge instabilities, will allow Consorzio RFX to continue experimental research on plasmas with Reversed Field Pinch and other magnetic confinement methods. To measure the ion temperature, the ion speed, the impurity content and the magnetic field in the plasma core, the Charge Exchange Recombination Spectroscopy (CXRS) and Motional Stark Effect (MSE) diagnostics require the injection of a neutral beam.
The project NEFERTARI, with its Work Package 5, aimed at upgrading the RFX-mod diagnostic Neutral Beam Injector (DNBI), which could not be operated due to technical faults, to the obsolescence of several components and to high voltage safety issues. The open-cycle cryogenic pumping system was substituted with a commercial one, to ensure economic sustainability against helium costs. The duct between the DNBI and the toroidal chamber was redesigned and manufactured, to reduce beam reionization losses. Contemporarily, the CXRS and MSE diagnostics were designed and the main instrumentation was procured.
This contribution presents an overview of the activities and of the results, with a focus on the new electric systems and control systems for the DNBI.

Speaker: Marco BARBISAN (CNR, Istituto per la Scienza e Tecnologia dei Plasmi)

Barbisan_workshopNEFERTARI.pdf

17:00 → 17:20 Development of Advanced Experimental Facilities for High-Voltage Insulation Studies within the NEFERTARI Project

The design and operation of magnetic confinement fusion devices and associated high-power systems require reliable electrical insulation solutions capable of operating under extreme conditions. In particular, several subsystems of fusion facilities—such as Neutral Beam Injectors (NBIs) and high-power transmission infrastructures—operate at high or extra-high voltage levels, where insulation performance becomes a critical technological challenge. Within the NEFERTARI project, Work Package 6 has been devoted to the development of an advanced experimental laboratory for the investigation of high-voltage insulation phenomena relevant to fusion applications, focusing on both vacuum and pressurized gas environments.
The activities have been carried out at the High Voltage laboratory of the Industrial Engineering department of the University of Padova, where the High Voltage Padova Test Facility (HVPTF) has been operating since 2010. The facility is capable of performing high-voltage DC tests in high and ultra-high vacuum conditions, applying voltages up to 800 kV on a single vacuum gap. One of the main objectives of the work package was the refurbishment and upgrade of the existing experimental setup dedicated to vacuum insulation studies. Vacuum represents an attractive insulating medium due to its environmental compatibility and its excellent dielectric properties; however, the physical mechanisms governing electrical breakdown in vacuum remain only partially understood despite decades of experimental investigations. The upgrade of the HVPTF facility involved the improvement of the vacuum system, the installation of new high-voltage feedthroughs, the enhancement of diagnostic capabilities, and the implementation of improved environmental control of the laboratory. These upgrades were necessary to increase the reliability of the system and to mitigate the effects of energetic vacuum arcs that may occur during high-voltage experiments, enabling more stable and reproducible experimental campaigns.
In parallel, a second major objective of WP6 was the design and realization of a completely new experimental facility dedicated to the study of electrical insulation in pressurized gases under high-voltage DC conditions. Gas-insulated transmission technologies are widely used in high-power electrical systems due to their compactness, high reliability, and low transmission losses. In fusion facilities, Gas Insulated Lines (GIL) represent an attractive solution for supplying high-power systems such as Neutral Beam Injectors. However, while AC gas-insulated technologies are mature and widely adopted in industrial applications, several open issues remain in the case of HVDC systems. In particular, the stationary electric field distribution along insulating structures under DC voltage is strongly influenced by charge transport processes and charge accumulation at gas–solid interfaces, which can significantly affect insulation performance and reduce the flashover voltage.
The new experimental facility developed within WP6 includes a real-scale pressurized vessel equipped with high-voltage bushings, electrodes, and dedicated diagnostic systems, together with a high-voltage DC power supply rated up to 500 kV and a dedicated data acquisition and control system. This infrastructure enables systematic investigations of insulation phenomena in gas-insulated HVDC systems, including the study of charge carrier transport, surface charge accumulation, dark currents injected by high-voltage electrodes, and the influence of environmental factors such as temperature, humidity, and particle contamination. Particular attention is also devoted to the investigation of alternative insulating gases and gas mixtures with lower environmental impact than SF₆, contributing to the development of more sustainable solutions for high-voltage technologies.
In addition to experimental investigations, the experimental activities also support the development and validation of advanced numerical models for the simulation of electro-quasi-static phenomena in HVDC gas-insulated systems. These models aim at capturing the complex interaction between electric fields, charge transport mechanisms, and material properties, including effects such as radiation-induced conductivity (RIC) that may occur in fusion environments. The combined experimental and modeling approach provides a powerful framework for improving the understanding of insulation phenomena and for supporting the design of reliable high-voltage components for future fusion devices.

Speaker: Nicolò MARCONATO

Nefertari_FinalWorkshop_Marconato.pdf

17:20 → 17:40 WP-8: Laboratory for innovative diagnostics for imaging of soft X-rays and neutrons

RFX-Mod 2 will feature a suite of new, state-of-the-art plasma diagnostics. Work Package 8 is responsible for developing two of these diagnostics, specifically the X-ray imaging diagnostic and the 2.5 MeV neutron diagnostic. The first one is based on the Gas Electron Multiplier (GEM) concept. The second one is based on lanthanum chloride scintillator crystals. In addition to developing, designing, and assembling these two diagnostics and installing them on RFX Mod 2, WP8 took care of the realisation and implementation of a full laboratory/facility aimed at designing, assembling, and testing of detectors for plasma science applications. The premises acquired through the NEFERTARI project are, more specifically:
- a Test Irradiation Area (a large shielded room with a set of X and gamma-ray sources dedicated to the test od detectors)
- a Detector Assembly Unit (a large Clean Room for the assembly of critical detector parts)
- an additive manufacturing lab, equipped with a series of 3D printers aimed at the internal design and production of detector parts like frames, supports etc.
With these innovations, integrated into the previous structures of the ISTP-CNR in Milan (which offer, among other things, the possibility of absolutely calibrating the X-ray and gamma detectors), the ISTP laboratory increases its capabilities as an infrastructure capable of taking care of the design, construction, testing and maintenance of various types of nuclear diagnostics for applications in plasma physics.

Speaker: Enrico PERELLI CIPPO (Istituto per la Scienza e Tecnologia dei Plasmi - CNR)

Nefertari_FinalWorkshop_WP8_EPC_1.0.pptx

17:40 → 18:00 WP9 - Research and Development of optical plasma diagnostics and modelling for fusion

In this WP we have developed two facilities, one experimental, the other one theoretical, based on the expertise of the Bari group in the diagnostics and modelling of non-equilibrium plasmas.
The experimental facility is a projection of our consolidated expertise in the optical diagnostics of gas discharges into applications to fusion-relevant studies and the development of new diagnostic strategies. In particular, we have acquired instrumentations for three main diagnostic applications:
1. Installation for studies on Laser Induced Breakdown Spectroscopy (LIBS) by fs laser, for the in-situ elemental analysis of surface modifications and, in particular, fuel retention in plasma facing materials. The relevant instrumentation is a fs laser facility, a state-of-the arts spectrograph and a set of optical microscope/optical profilometer to characterize the craters made by the laser for a quantitative depth profilometry;
2. Installation for optical emission spectroscopy, to support CR models of hydrogen emission. The relevant instrumentation is a fast gated optical spectrograph;
3. Installation for laser spectroscopy studies, with a double aim. One is the study of the kinetics of electronic states of hydrogen, to support the CR models, for which a tuneable ps OPO laser has been acquired. The other aim is the analytical application of Laser Induced Fluorescence (LIF) to the detection of transient species and, in particular H atoms, for which a ns tuneable laser has been acquired capable of wavelengths down to 204 nm.
Studies and developments of diagnostic techniques require small scale plasma test facilities that can run continuously and every day, on which the diagnostics can be tested, improved and adapted to the final user’s demands. To this end we have developed and built two discharge systems based on a DC reflex IBC discharge scheme which is capable of high-density plasma production even at low, order of 1 Pa, gas pressure. One of these discharges, with two cathodes, is used for loading with deuterium test samples for LIBS and for discharge-assisted LIBS. The other, with 8 cathodes, will be used for spectroscopy studies.
An important part of the project has been the refurbishment of new laboratory space, with technical installations, to accomodate the huge amount of new instrumentation. This operation has been made in the building of the Department of Physics of the University of Bari, where we were already present with smaller labs and with teaching activities on discharge and plasma physics. The increase of space and facilities in the Physics Department paves the way for a penetration of nuclear fusion issues into the University of Bari and for a fruitful exchange in terms of both scientific expertise and availability of new research personnel.
The Computational lab pursued two objectives:
1. Numerical simulation of negative ion source for neutral beam Injection, with the development of s three-dimensional PIC code and of a Collisional-Radiative model for the interpretation of emission spectra, in close connection with the OES experimental activities.
2. Numerical simulation of plasma-wall interaction in the Divertor region.
The numerical laboratory has enriched its calculus facilities by the acquisition of two workstations where the codes can be tested prior to launching them of large supercomputers.
This modelling facility will project its work beyond the present project, in close connection with the experimental activity in the infrastructure, along four topical areas: i) calculation of state selective cross section for elementary processes in bulk and surface; ii) interface between plasma and solid-state physics; iii) control of plasma-external power coupling, iv) coherent structures in magnetized plasma.

Speaker: Giorgio DILECCE (CNR - ISTP)

NEF_Dilecce.pptx

Thursday 26 March

09:00 → 11:00 RFX experimental plants: -

Conveners: Giuseppe DI GIRONIMO (Università degli Studi di Napoli Federico II), Matteo BROMBIN (Consorzio RFX)

09:00 → 09:15 Upgrade and Optimization of the Vacuum System for RFX-mod2 within the NEFERTARI Project

The RFX experiment has been in operation since 1991. Subsequently, following significant upgrades to the toroidal assembly and power supply systems, RFX-mod began operation in 2004, while the original vacuum and gas injection systems remained unchanged.
Thanks to funding obtained within the framework of the NEFERTARI project under the Italian National Recovery and Resilience Plan (PNRR), a project was launched to design and construct a new vacuum system specifically conceived to serve and support the experimental activities of RFX-mod2.
The main functions of the vacuum system are:

• evacuation of the vacuum vessel from atmospheric pressure down to operational conditions (10-6-10-7 mbar);
• maintenance of proper vacuum conditions inside the vessel during experimental operations (H₂, D₂, He) and during first-wall conditioning processes (GDC, PDC, boronization).

The upgrade involved the complete refurbishment of the fore-vacuum section, including the installation of two primary pumping units, each consisting of a roots pump combined with a screw pump, along with the corresponding DN160 piping. For the high-vacuum section, the existing turbomolecular pumps (featuring a weighted rotor design) were retained, while new sensors and valves were installed to improve control and operational reliability.
The control system was entirely redesigned to manage not only the vacuum plant and the injection systems, but also the boronization plant.
The management of the supply contract, the most economically significant within the NEFERTARI project, required close collaboration among ISTP, CRFX, and the contractor company, highlighting the importance of effective coordination between research institutions and industry in the realization of complex high-performance facilities.

Speaker: Matteo ZAUPA (CNR-ISTP)

zaupa.pptx

09:15 → 09:30 Glow Discharge cleaning efficiency analyses in view of RFX-mod2 operation

RFX-mod2 is the upgraded version of the RFX-mod experiment, a toroidal plasma confinement device, with a major radius of 2 m and a minor radius of 0.5 m, capable of operating in both Reversed Field Pinch and Tokamak configurations. RFX-mod2 is presently under re-assembly at Consorzio RFX (Padova, Italy) after substantial modifications aimed at increasing the plasma volume and optimizing its position with respect to the active and passive components of the Magnetohydrodynamic (MHD) control system, enabling the exploration of plasma regimes with higher temperature and improved stability. As in all magnetic confinement devices, the initial operational phase requires
effective first wall conditioning, typically performed by Glow Discharge
Cleaning (GDC). The GDC system of RFX-mod2 has been significantly upgraded
and now includes eight new fixed electrodes, which will act as Plasma
Facing Components (PFCs), together with two movable electrodes designed
for the boronization procedure. The new configuration is intended to improve
plasma uniformity and enhance the overall efficiency of the wall conditioning
process.
This work presents the first experimental results obtained during hydrogen
and helium discharges using the new fixed electrodes. Experimental
campaigns have been carried out in a dedicated facility where representative
first wall materials for RFX-mod2 — including alumina-coated copper
components, graphite tiles, and Torlon 5030 support rings — are installed.
Plasma temperature and density measurements have been performed as a
function of probe position and electrode feeding power. In addition, Residual
Gas Analysis (RGA) and optical spectroscopy diagnostics have been used to assess the effectiveness of the GDC process.
The results provide key information on the operational reliability and
conditioning performance of the upgraded GDC system, contributing to the
optimization of future RFX-mod2 plasma-wall conditioning campaigns.

Speaker: Michele FADONE (CNR)

Nefertari_FinalWorkshop_WP1_MF.pptx

09:30 → 09:45 Integration of the Pulse Discharge Cleaning system in RFX-mod2

The Pulse Discharge Cleaning (PDC) is a system that will be used in RFX-mod2 to clean the first wall through repeated low-current pulses of about 50 kA. It comprises three main power supplies, each dedicated to a different set of magnets. One generates an oscillating pulse of 10 kA with a duration of a few ms, repeated every 2 s, another provides a static toroidal field of 50 mT, and the third generates a vertical poloidal field to facilitate the plasma discharge.
The current system was installed in the early 2000s for RFX-mod, the previous iteration of the experiment, however its completion, including the connection to the magnets of RFX-mod and its full commissioning, never took place. In the last few years, in view of the start of operations of RFX-mod2, a significant effort has been conducted to bring this system to operational readiness.
Thanks to funding obtained within the framework of the NEFERTARI project under the Italian National Recovery and Resilience Plan (PNRR), the missing components required to enable the operation of the PDC have been procured and installed. The main procurement items were the medium-voltage disconnectors, needed to isolate the PDC power supplies from the magnets during normal experimental operation, the laying of the missing medium-voltage cable connections, and a snubber circuit to reduce the voltage derivative on the magnetizing magnet of RFX-mod2 used for PDC operation. The installation and commissioning of these components have been successfully completed, and the system is currently undergoing an integrated commissioning to verify the correct operation of all subsystems prior to its use in the RFX-mod2 experimental campaign.

Speaker: Francesco SANTORO (Consorzio RFX)

PDC_PNRR_r0.1.pptx

09:45 → 10:00 FARHA-ONE: Remote Handling Test and Training facility for RFX-mod 2. From requirement elicitation to experimental validation

This work presents the research coordination and supervisory activities carried out within the NEFERTARI project, targeting the development of a robotic remote handling system for inspection and maintenance operations inside the RFX-mod2 fusion machine. The contribution spans the full engineering lifecycle, with direct involvement in requirement elicitation and formalization, conceptual definition of the kinematic and mechatronic architecture, and design of the overarching software architecture, alongside the supervision of a multidisciplinary research team covering mechanical design and software development.

The adopted methodology is grounded in a structured, requirement-driven engineering approach that systematically translates environmental, operational, and reactor-specific constraints into coherent technical specifications across all levels of system abstraction. The confined geometry environment of RFX-mod2 imposes stringent demands on system compactness, accessibility through limited ports, mechanical reliability, and remote operability in the absence of direct sensor feedback — constraints that governed both the kinematic concept and the software architecture strategy. The latter integrates flexible-body simulation, real-time control, collision avoidance based on distance-field representations, and immersive Digital Twin visualization within a modular framework supporting human-in-the-loop operation and operator training. The research activity culminated in the successful realization and experimental validation of the complete system, demonstrating the effectiveness of the proposed integrated approach and offering a generalizable methodological contribution to the field of robotics for confined and hazardous environments.

Speaker: Andrea FONTANELLI (Università degli Studi di Napoli Federico II)

10:00 → 10:15 FARHA-ONE: Remote Handling Test and Training facility for RFX-mod 2. Designing and Validating Multitasking Robots in Confined Environment

This work presents the systematic design, realization, and experimental validation of a serial articulated robotic manipulator conceived for remote handling operations in confined and highly constrained environments. The work addresses the intrinsic complexity of developing robotic systems for such contexts by adopting a rigorous, requirement-driven engineering methodology that ensures coherence between operational needs, design choices, and experimental outcomes. Starting from a structured elicitation of stakeholder and application requirements, the proposed approach translates functional and environmental constraints into clear technical specifications governing kinematic architecture, mechanical layout, actuation strategy, and system integration. These specifications form the basis for the conceptual and detailed design of a compact, multi-degree-of-freedom manipulator capable of operating through limited access ports while maintaining adequate stiffness, payload capacity, and controllability. The design phase is supported by analytical and numerical methods, including kinematic modeling, actuator sizing, and structural analyses, which guide critical decisions on link geometry, joint architecture, and transmission solutions. Attention is devoted to the integration of the manipulator within a dedicated remote handling facility, specifically developed to replicate the geometric and operational conditions of the target environment and to enable controlled testing and qualification activities. The validity of the proposed methodology is demonstrated through the physical realization of the robotic arm and its successful experimental assessment. Factory-level tests confirm the consistency between predicted and measured performance in terms of deflections, alignment, and operational behavior. Beyond the specific system presented, the results highlight the robustness and transferability of the adopted design approach, providing a structured framework for the development of reliable robotic manipulators for confined-environment applications.

Speaker: Salvatore FUSCO (Università degli Studi di Napoli Federico II)

10:15 → 10:30 FARHA-ONE: Remote Handling Test and Training facility for RFX-mod 2. Remote Control of Flexible Robots using Digital Twins

This work presents a comprehensive framework for the modeling, simulation, and control of flexible robotic manipulators (FRMs), with a particular focus on remote handling applications in fusion machines. The work is motivated by the limitations of classical rigid-body assumptions when applied to long-reach, lightweight, high-degree-of-freedom robotic systems, as well as the challenges in accurately controlling and simulating these robots in constrained or hazardous environments where direct access to sensors is limited and interactions with the environment significantly affect system behavior. The proposed approach is based on a Digital Twin architecture that integrates geometrically exact flexible-body modeling with real-time, human-in-the-loop control. The simulation of FRMs relies on an efficient formulation capable of capturing large deformations while remaining suitable for real-time execution. These models are embedded within a modular software architecture that combines flexible-body simulation, vibration suppression, optimal control, collision detection based on distance-field representations, and immersive visualization through a photorealistic virtual-reality Digital Twin. The framework is validated within the NEFERTARI project, targeting remote inspection and maintenance tasks inside the RFX-mod2 fusion machine. The results demonstrate the effectiveness of the proposed approach for the design, simulation, and control of long-reach manipulators, providing enhanced situational awareness, operator support, and training capabilities in scenarios where direct sensing is limited or unavailable.

Speaker: Alessandro SOFIA (Università degli Studi di Napoli Federico II)

10:30 → 10:45 Motion Planning and Robust Control of the Remote Handling System concerning RFX-mod2 within the NEFERTARI Project

Within the framework of the technological development activities associated with the RFX-mod2 experimental infrastructure and carried out in the context of the NEFERTARI project, a research activity was conducted focusing on motion planning and control of the robotic manipulator intended to perform remote handling operations. These developments are part of a broader program aimed at upgrading the technological infrastructure of the RFX facility in order to improve operational reliability and enhance experimental capabilities in the field of nuclear fusion research.
After updating the remote handling system with a novel kinematic model and therefore improving its dexterity in the operational workspace, based on this model a motion planning procedure is developed to generate desired end-effector trajectories that are consistent with the operational environment. The desired trajectories defined in Cartesian space are subsequently transformed into reference signals in joint space thanks to an inverse kinematic approach, thus obtaining the position profiles required for the electric actuators installed in the various joints of the manipulator.
In order to guarantee accurate tracking of the reference signals, dedicated controllers are designed for each individual motor, while explicitly considering the dynamics of the actuation system. In this context, a robustness metric is explicitly incorporated into the control design process, with the aim of ensuring satisfactory performance even in the presence of model uncertainties and unmodeled contributions, such as unknown external disturbances.
The performance of the entire closed-loop system is numerically verified. In particular, the robustness of the control system is further assessed by applying a disk margin approach; this analysis allows a quantitative evaluation of the system tolerance with respect to simultaneous gain and phase variations. The results highlight the capability of the proposed control architecture to guarantee stable and robust performance under the expected operating conditions.

Speaker: Jason BETTEGA (Università degli Studi di Padova)

Docs_uploaded.zip

10:45 → 11:00 Discussion: RFX experimental plants

Chair 1: Giuseppe Di Gironimo
Chair 2: Matteo Brombin

11:00 → 11:15 coffee break

11:15 → 11:45 Integrated Plasma Equilibrium Control in RFX-mod2 via Model Predictive Control

Magnetic confinement is widely recognized as one of the most promising strategies for achieving controlled thermonuclear fusion on Earth. In toroidal devices, the precise regulation of plasma equilibrium, including plasma current, position and shape, is essential to guarantee safe, stable and high-performance operation. In this framework, RFX-mod2 (Reversed Field eXperiment), the upgraded configuration of RFX-mod, represents a highly flexible experimental platform capable of operating in both reversed field pinch and tokamak configurations. The ongoing hardware refurbishment provides an opportunity for redesigning the magnetic control system. This work presents an integrated framework for plasma equilibrium control in tokamak operation of RFX-mod2, combining electromagnetic modeling, constrained optimal control, and real-time boundary reconstruction. A linear control-oriented plasma model is first computed using the CREATE-L code, explicitly accounting for the complex circuital interconnections between the poloidal field (PF) coils and the power supplies. A major challenge arises from the one-quadrant a.c.–d.c. converters driving the PF coils, which impose strict positivity constraints on the commanded voltages and significantly restrict the admissible control actions. To address these issues, the well-known Model Predictive Control (MPC) approach has been formulated for simultaneous plasma current and shape control. Unlike conventional two-layer architectures, the proposed MPC provides a unified optimization-based framework that explicitly embeds the electromagnetic model and actuator limitations within the control law. In particular, the controller incorporates shape control objectives by directly regulating plasma boundary descriptors through coordinated voltage references. This enables accurate tracking of desired equilibrium configurations while rigorously satisfying voltage constraints. Extensive simulation studies based on the RFX-mod2 model, including plasmaless discharge scenarios derived from experimental data of the previous RFX-mod device, demonstrate equilibrium control, effective constraint handling and robust multivariable performance. Furthermore, the computational feasibility of the proposed controller is assessed within the MARTe2 real-time framework envisaged for RFX-mod2 operations, confirming its suitability for practical implementation. To complete the control architecture, a physics-informed neural network approach for real-time plasma boundary reconstruction is also integrated in the control loop. The CARONTE algorithm leverages an Extreme Learning Machine to solve the homogeneous Grad–Shafranov equation using magnetic sensor measurements, enabling real-time training and therefore adapting the network to the evolving plasma equilibrium. Compared with other Neural Network-base reconstruction approaches, the CARONTE eliminates the need for extensive offline training datasets.
Overall, the integration of electromagnetic modeling, optimal constrained predictive control with explicit shape regulation and physics-informed data-driven reconstruction provides a coherent and computationally viable framework for advanced plasma equilibrium management in magnetic confinement experiments in the RFX-mod2 device.

Speakers: Dr Dario Giuseppe LUI (Università degli Studi di Napoli Federico II), Dr Federico FIORENZA (Consorzio CREATE)

Integrated Plasma Equilibrium Control in RFX-mod2 via Model Predictive Control_Parte1.pdf

Integrated Plasma Equilibrium Control in RFX-mod2 via Model Predictive Control_Parte2.pdf

11:15 → 12:00 Plasma diagnostic and modeling: part 1

Conveners: Lorella CARRARO (ISTP-CNR- Consorzio RFX), Marco TARDOCCHI (ISTP CNR)

11:45 → 12:00 Three-dimensional modeling of RFX-mod2 experiment for magnetic control of exotic tokamak plasma regimes

Three dimensional (3D) effects play a crucial role in the stability and control of magnetohydrodynamic (MHD) instabilities in toroidal confinement devices, particularly when the plasma operates in naturally unstable regimes such as “low-$q$” (Lq) and “ultra-low-$q$” (ULq) configurations. Plasmas in such “exotic'' regimes are intrinsically unstable to ideal MHD modes and the control of resistive wall modes (RWMs) is mandatory for the experiment success.
Non axisymmetric features of the surrounding conducting structures and of the control coils can significantly modify the MHD plasma stability and the effectiveness of active control schemes. As a consequence, accurate 3D modeling is essential to correctly predict the mode growth rate and its spatial structure, evaluate passive stabilization provided by the surrounding conducting structures, and design robust feedback control strategies.

In this contribution, the main non axisymmetric features of RFX-mod2, a major upgrade of the former RFX-mod, are presented and the solutions adopted for their modeling are described.
One of these solutions has been integrated into the CarMa code, which couples the linearized MHD solver MARS-F with the CARIDDI code, that solves the eddy current problem in a three dimensional formulation. This coupling enables a consistent description of the dynamics of the RWM for an upper single null plasma equilibrium with $q_a < 2$, leading to a state space representation of the system.
The resulting state space model, following an order reduction, has been implemented in a Matlab-Simulink application for dynamic modeling of the instability evolution and control.
A nominal full state-feedback controller based on pole placement has been sketched, generally demonstrating RWM control in RFX-mod2 with model-based techniques. As an upgrade, a model-predictive controller has been designed and applied. The obtained results indicate the feasibility of shaped low-$q$ experiments with active control of RWM in this device.

Speaker: Andrea CORBIOLI (University of Padua/RFX Consortium)

Corbioli_Nefertari_FinalWorkshop_v2.pdf

12:00 → 13:00 Visita guidata all'Orto Botanico

13:00 → 14:00 pausa pranzo

14:00 → 16:30 Plasma diagnostic and modeling: part2

Conveners: Lorella CARRARO (ISTP-CNR- Consorzio RFX), Marco TARDOCCHI (ISTP CNR)

14:00 → 14:15 WP-3 Innovative Diagnostics for Edge Fusion Plasmas: Light Impurity Tomography and MANTIS polychromator

The plasma edge plays a key role in determining confinement and stability in fusion devices, governing heat and particle transport to plasma-facing components. Reliable, high-resolution diagnostics are therefore essential to characterize edge plasma properties and their dynamics.
A comprehensive set of spectroscopic diagnostics has been successfully developed and implemented to investigate plasma–wall interaction and light-impurity behavior at the edge of the RFX-mod2 device. The Light Impurity Tomography (LIT) system was designed, realized, assembled, and calibrated, providing a flexible tomographic tool for measuring the spatial emissivity distribution of Hα radiation and light impurities. The system consists of seven cameras distributed along the full poloidal cross-section, enabling both radial and poloidal resolution of particle influxes from the first wall and allowing detailed studies of the interaction between particle sources and the three-dimensional magnetic field structure.
In parallel, the MANTIS spectroscopic diagnostic was developed to obtain two-dimensional, wavelength-resolved images of edge plasma emission. The optical design and realization of a dedicated polychromator, combined with in-vessel mirrors and coherent fiber bundles, enabled tangential viewing of the plasma edge. The polychromator architecture, based on concave mirrors, lenses, and interferential filters, allows the simultaneous detection of emissions from different impurity species using multiple cameras. Laboratory assembly, alignment, and testing confirmed the diagnostic performance and spatial resolution.
A key outcome of these diagnostics is their capability to support three-dimensional reconstructions of edge plasma emissivity. Such 3D reconstructions are particularly crucial in devices like RFX-mod2, where intrinsically three-dimensional magnetic configurations and perturbations strongly influence plasma–wall interaction and impurity transport. The combined use of tomographic and spectroscopic imaging enables a more realistic representation of the edge plasma, improving the interpretation of impurity sources, transport mechanisms, and their coupling with complex magnetic topologies.
Together, the LIT and MANTIS diagnostics provide complementary and spatially resolved measurements of main gas and impurity influxes, delivering advanced experimental tools to assess the role of three-dimensional effects on plasma–wall interaction and impurity control in fusion plasmas.

Speaker: Margherita UGOLETTI

presentazione_ISTP_nefertari_workshop_PD.pdf

14:15 → 14:30 Advanced plasma edge measurements with the Thermal Helium Beam diagnostic

The Thermal Helium Beam (THB) diagnostic provides simultaneous measurements of electron temperature ($T_{e}$) and density ($n_e$) profiles in the plasma edge and scrape-off layer (SOL) using helium line ratios interpreted through a collisional–radiative model (CRM). For the RFP experiment RFX-mod2, a new-generation THB system has been designed and experimentally validated at the TCV tokamak. The diagnostic extends the conventional three-line configuration (667.8, 706.5, 728.1 nm) with a fourth He I emission line at 501.6 nm, enabling direct assessment of radiation re-absorption effects.
This upgrade is essential in the far SOL, where radiation trapping under conditions of high neutral helium density and low $T_{e}$ and $n_{e}$ can significantly affect the line intensities. For the first time in a tokamak, the impact of radiation re-absorption on $T_{e}$ and $n_{e}$ reconstruction has been experimentally quantified, demonstrating that its inclusion in the CRM is necessary for accurate edge profile measurements.
Beyond steady-state reconstruction, the THB enables time-resolved studies of edge dynamics. In Type-I ELMy H-mode plasmas at TCV, coherent inter-ELM fluctuations, mainly associated with density perturbations, were detected and radially localized. The diagnostic also allowed investigations of profile evolution during the ELM cycle and of turbulence-driven transport.
The validated four-line THB thus provides a robust tool for edge kinetic, fluctuation, and turbulence studies. In RFX-mod2, it will support accurate profile characterization and their temporal evolution, as well as poloidal profile reconstructions, contributing to a deeper understanding of edge transport and plasma-wall interaction processes.

Speaker: Miriam LA MATINA (Consorzio RFX, C.so Stati Uniti 4, 35127 Padova, Italy)

presentazione_ISTP_THB2.pptx

14:30 → 14:45 Magnetic topology and ion dynamics during magnetic reconnection events in RFX-mod

During typical high-current Reversed Field Pinch (RFP) discharges, long phases of improved confinement with helical symmetry are occasionally interrupted by magnetic reconnection events, which cause weakening of plasma confinement and consequently significant Plasma-Wall Interaction (PWI)~\cite{Zanca_JNuclMat_2007, Gobbin_NF_2022}. This work aims at determining the role of tearing mode phase-locking in driving PWI in RFX-mod, as captured by a fast camera imaging the graphite-covered inner wall~\cite{Scarin_NF_2019}.

An initial analysis based on a three-dimensional Connection Length map~\cite{Schmitz_NF_2008}, computed using the Hamiltonian guiding-center code \orb~\cite{White_ORBIT}, indicates that $m = 1$ tearing modes play a primary role in shaping the PWI pattern. Moreover, it highlights a previously unreported contribution of the $m = 0$, $n = 7$ mode to the observed PWI~\cite{Agostini_NF_2017, Spizzo_NF_2017}. Connection Length map reproduces the PWI features in detail, suggesting the presence of complex hidden structures in the magnetic topology associated with stocasticity and enhanced particle losses~\cite{Spizzo_CHAOS}. A more refined analysis considering the dynamical properties of Maxwellian ions simulated in \orb~confirms the dual PWI topological nature during the event~\cite{Porcu_PoP}. These results emphasize the need for advanced diagnostic systems and improved control of tearing mode dynamics. The upcoming RFX-mod2 upgrade~\cite{Marchiori_FED_2017, Marconato_FED_2019}, including enhanced magnetic pickup arrays and a system of seven fast cameras, will enable a more precise characterization of these interactions and their relation to tearing modes phase-locking phenomena.

Moreover, the first implementation in \orb~of a three-dimensional electrostatic potential calculated by the three-dimensional MHD code Specyl~\cite{Cappello_Biskamp} is shown to be a fundamental key for understanding the thermal content behavior during magnetic reconnection, which had not been fully disclosed by numerical methods. Such analysis shows that magnetic reconnection events preferabily deplete the thermal content of the plasma and accelerate particle towards the wall~\cite{Spizzo_PPCF_2026}, coherently to what already observed experimentally via the Neutral Particle Analyzer (NPA) diagnostic~\cite{Anderson_PoP_2016}.

The NPA measurements constistute a fundamental instrument to understand the correlation between the onset of magnetic reconnection and the loss of accelerated particles at the plasma edge. This work also includes a preliminary refurbishment activity made on the diagnostic in perspective of the upgraded RFX-mod2~\cite{Marrelli_NF_2019, Carraro_NF_2024}, namely the calibration in time and energy of the acquisition system based on the CAEN 2730 digitizer.

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L. Marrelli \textit{et al.}, \href{https://iopscience.iop.org/article/10.1088/1741-4326/ab1c6a}{Nucl. Fusion} \textbf{59}, 076027 (2019)
\bibitem{Carraro_NF_2024}
L. Carraro \textit{et al.}, \href{https://iopscience.iop.org/article/10.1088/1741-4326/ad490a}{Nucl. Fusion} \textbf{64}, 076032 (2024)

Speaker: Pasquale PORCU (Università degli Studi di Padova - CRF; Consorzio RFX)

Porcu_vers4.pdf

14:45 → 15:00 Turbulence simulations of RFX-mod tokamak and reversed field pinch plasmas

One the greatest uncertainties in the success of magnetically confinement fusion is related to turbulent transport in the boundary region of fusion devices, which controls the heat flux to the wall and the access to high confinement regimes. Because of the wide range of spatial and time scales that characterize turbulence in magnetic confinement plasma devices and the complex magnetic geometries, a deep understanding of turbulent transport in this region can only be attained by combining highly-resolved measurements with the results of complex three-dimensional turbulence simulations.
RFX-mod (Consorzio RFX, Padua, Italy) is a flexible machine that can operate both as high-confinement (H-mode) tokamak and as high-current Reversed Field Pinch (RFP). This unique feature allows for a direct comparison of boundary turbulence in the two very different magnetic configurations. The RFX-mod turbulence simulations presented here are carried out with the state-of-the-art GBS code [1].
The first part of the talk is devoted to turbulence simulations of a RFX-mod diverted plasma in the presence of a biasing electrode, which has been recently implemented in GBS. The simulations show a strong suppression of turbulent transport caused by the flow shear generated by the biasing electrode, leading to the formation of an edge transport barrier with a pedestal-like structure, which agrees qualitatively and quantitatively with RFX-mod experiments [2].
The results of pioneering global flux-driven turbulence simulations in RFP plasmas are presented and discussed in the second part of the talk. These simulations are performed considering (i) a self-organized magnetic field that features multiple magnetic islands and significant magnetic chaos, and (ii) a simplified magnetic field where only the dominant magnetohydrodynamics modes are retained. A comparison between these two cases reveals a relatively weak effect of magnetic chaos on turbulence, while the electrostatic radial electric field is found to be deeply influenced by stochastic transport.

References
[1] M. Giacomin et al. J. Comput. Phys. 463 (2022) 111294.
[2] M. Giacomin et al. Nucl. Fusion 65 (2025) 036013.
This work has been funded by the European Union - NextGenerationEU (“NEFERTARI – New Equipment for Fusion Experimental Research and Technological Advancements with Rfx Infrastructure”). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. We acknowledge EuroHPC JU for awarding the project ID EHPC-REG-2024R02-031 access to Discoverer HPC (Sofia Tech Park, Bulgaria) and CINECA (Italy) for awarding access to Leonardo HPC under the ISCRA initiative (project ID IscrB_GBSRFP).

Speaker: Maurizio GIACOMIN (University of Padua)

Boundary_turbulence_RFX_NEFERTARI.pptx

15:00 → 15:15 Advanced Electromagnetic Modeling for Magnetic Confinement Fusion Devices and High-Voltage Gas-Insulated Components within the NEFERTARI Project

The development of reliable numerical tools for electromagnetic (EM) analysis is a key requirement for the design and operation of magnetic confinement fusion devices and associated power supply systems. Within the NEFERTARI project, advanced modeling strategies are being developed to address complex EM phenomena occurring both in large conductive structures surrounding the plasma and in high-voltage direct current gas-insulated systems (HVDC-GIS) used in fusion-related power infrastructures.
The first part addresses the modeling of eddy currents induced in passive conductive structures of fusion machines. The adopted framework is based on an Integral Equation Method (IEM) with a mixed volume–surface formulation, enabling the simultaneous treatment of thick conductors with volumetric elements and thin structures with surface elements. To enable the simulation of large-scale devices, advanced hierarchical matrix (H-matrix) approaches, have been considered in conjunction with Model Order Reduction (MOR) techniques. Projection-based reduced-order models are constructed offline and allow rapid evaluation of induced currents and electromagnetic quantities during transient events. These reduced models are particularly attractive for fast scenario analysis and for the development of digital-twin frameworks aimed at monitoring electromagnetic loads and structural responses in fusion devices.
The second part of the work focuses on EM modeling challenges in HVDC-GIS used in power supplies for NBI. In fusion environments, radiation fields can modify the dielectric properties of insulating gases through radiation-induced conductivity (RIC), affecting electric field distributions and promoting surface charge accumulation at gas–solid interfaces. Advanced electro-quasi-static models coupled with charge transport formulations are investigated to capture these effects and assess their impact on insulation performance.

Speaker: Francesco LUCCHINI (Department of Industrial Engineering, University of Padova)

Nefertari_FinalWorkshop_Lucchini.pdf

15:15 → 15:30 Redesign of the DNBI Vacuum System for RFX-mod2 within the NEFERTARI Project

In RFX-mod, several plasma measurements would have benefited from improved accuracy, particularly magnetic field diagnostics, while key core measurements such as ion temperature, impurity density, and impurity flow were not available. These quantities are of high relevance for the investigation of QSH and SHAx plasma states. For this reason, the RFX-mod2 upgrade includes the implementation of Charge eXchange Recombination Spectroscopy (CXRS) and Motional Stark Effect (MSE) diagnostics, whose development status is presented in this work.

The operation of these diagnostics requires a high-quality neutral beam, motivating the optimization of the Diagnostic Neutral Beam Injector (DNBI) transmission line in order to maximize the equivalent neutral current entering the RFX-mod2 vacuum vessel. Steady-state simulations identified beam reionization losses as being primarily localized in the connecting duct between the DNBI and RFX-mod2, which was consequently redesigned to minimize such losses.

In addition, to ensure economically sustainable operation of the DNBI, the original open-cycle cryopumps (2 × 24 kL/s) were replaced with closed-cycle units (2 × 10 kL/s), eliminating helium consumption but significantly reducing the available pumping speed. This change required a revalidation of the vacuum system and was explicitly taken into account during the duct redesign, including an assessment of the impact of the new equilibrium pressure on beam reionization losses.

Simulation results were compared with experimental data from previous RFX-mod campaigns, where DNBI transmission losses were observed to be significantly higher than expected. The analysis indicates that the measured losses exceed steady-state reionization predictions by approximately one order of magnitude, ruling out RFX-mod neutral gas filling pressure as the primary source of reionization of the observed past anomalies.

Speaker: Luca CINNIRELLA (Consorzio RFX)

presentation.pdf

15:30 → 16:15 Development of soft X-ray and neutron diagnostics for space-resolved spectroscopic measurements at RFX-mod2

The upgrade of RFX-mod (RFX-mod2) requires advanced diagnostics capable of providing space-resolved and energy-resolved measurements during Magnetic Reconnection (MR) events, which are fast transient phenomena characterized by intense bursts in particle flux at the detectors. In this context, this work focused on the development of soft X-ray (SXR) and neutron/gamma diagnostics for RFX-mod2, together with dedicated software for simulations and data analysis.

For the SXR diagnostic, an energy-resolved detection system based on Gas Electron Multiplier (GEM) detectors has been designed, accounting for the main challenges imposed by the RFX-mod2 environment, including operation in strong magnetic fields and possible detector gain variations. A custom simulation software, named REVOLT-U, has been developed to model the energy-resolved response of SXR pixelated detectors in nuclear fusion experiments. Its application to the development of an energy-resolved 1D tomographic reconstruction algorithm for RFX-mod2, and to the design of the SXR diagnostic system, supported the realization of a three-dimensional Computer-Aided Design (CAD) model of the diagnostic. The diagnostic is characterized by significant flexibility, as its parameters can be adapted to a wide range of operating conditions, depending on the experimental target and the plasma scenario.

As a neutron/gamma diagnostic for RFX-mod2, a system combining EJ-276D plastic scintillators and LaCl$_3$:Ce inorganic scintillators has been proposed.
The three-dimensional CAD model of the diagnostic system has been completed, with the detectors positioned as close as possible to the RFX-mod2 device in order to maximize the neutron flux, while ensuring adequate detector shielding for background mitigation and the definition of three lines of sight (allowing a basic level of spatial resolution).
The main challenge was identified in the potentially high magnetic fields at the detectors location ($\sim$ hundreds of mT), which led to the adoption of silicon photomultipliers (SiPMs) as photodetectors.
To address the potential challenges posed by pile-up, complex radiation fields, and the use of SiPMs coupled with LaCl$_3$:Ce scintillators, a neural network-based algorithm was developed for automated waveform processing, including pulse shape discrimination and pile-up recovery. This algorithm enables operator-independent particle identification and the recovery of events affected by pile-up. This can lead to a significant increase in the number of usable events compared to ideal pile-up rejection schemes, depending on the incident fluxes at the detectors and the observed pile-up probability.

The proposed neutron/gamma and SXR diagnostics will be installed in the same poloidal sector of RFX-mod2, providing simultaneous information on ion and electron acceleration during MR events, resolved in space, energy, and time.
Gamma-ray spectroscopy with spatial information could also contribute to the study of runaway electrons in future RFX-mod2 tokamak discharges.

Speakers: Andrea DAL MOLIN (Istituto per la Scienza e Tecnologia dei Plasmi - CNR), Federico GUIOTTO (Consorzio RFX), Oscar PUTIGNANO

Guiotto_NEFERTARI_WORKSHOP2026_PRESENTATION_FINAL_VERSION(REDUCED_dalMolin_Putignano)_v2.pdf

16:15 → 16:30 discussion - plasma diagnostics and modeling

Chair 1: Lorella Carraro
Chair 2: Marco Tardocchi

16:30 → 16:45 coffee break

16:45 → 17:00 Plasma–Neutral Modelling for the BiGyM Linear Device

Plasma–material interactions represent a key challenge for future nuclear fusion reactors and are widely investigated in linear plasma devices. The GyM [1] linear device, hosted at ISTP-CNR in Milan, operated at plasma densities of $10^{15}-10^{17}\text{m}^{-3}$, electron temperatures below 15eV, and ion fluxes up to $10^{21}\text{m}^{-2}\text{s}^{-1}$, reproducing tokamak main chamber conditions. To extend the parameter space toward divertor-relevant regimes, characterised by plasma densities of $\sim10^{19}\text{m}^{-3}$ and ion fluxes up to $10^{23}\text{m}^{-2}\text{s}^{-1}$, GyM is being upgraded to BiGyM, within the framework of the NEFERTARI project funded by the NextGenerationEU programme.
In BiGyM, helicon–wave–sustained plasmas will be generated by two 10kW birdcage resonant antennas [2] operating at 13.56MHz, alike those used in the RAID [3] linear machine, capable to ensure high plasma densities. The device will also feature a revised magnetic configuration, a redesigned vacuum vessel, a novel sample holder, and new in–situ surface diagnostics.
Among BiGyM design activities to support the machine optimisation, this contribution focuses on detailed plasma-neutral modelling performed with SOLPS–ITER [4], a tokamak edge simulation code recently adapted to linear geometries.
Firstly, BiGyM modelling was informed by parametric studies of a RAID plasma, examining the impact of absorbed power, power density distribution, particle absorption at pumping surfaces, particle diffusion, and energy transport coefficients. RAID simulations were validated against experimental data.
Building on these results, BiGyM simulations predict plasma parameters and explore their dependence on injected power, gas pressure, magnetic field configuration and boundary conditions. Different working gases, including helium and argon, were considered to evaluate the overall plasma performance.
For representative helium discharges (B≈20mT, p≈0.8Pa, $P_\text{injected}≈3\text{kW}$), simulations predict electron densities $n_e$ in the range $(1.5-2.0)\times10^{19}\text{m}^{-3}$ and electron temperatures $T_e$ of 4–5eV along the axis, with particle fluxes $\lesssim 3.5\times10^{22}\text{m}^{-2}\text{s}^{-1}$, consistent with divertor-relevant conditions. Under similar operating conditions, argon plasmas are predicted to reach densities of $\sim2\times10^{18}\text{m}^{-3}$ and electron temperatures of ~9eV along the axis, with particle fluxes $\lesssim 6\times10^{21}\text{m}^{-2}\text{s}^{-1}$. The results show good left–right symmetry of plasma parameters and indicate that variations in magnetic configuration modify them by less than 15%, assuming a fixed absorbed power density. By doubling the absorbed power, $n_e$ increases by about 70%, while $T_e$ increases by approximately 10%.
The predicted plasma conditions meet the performance targets set for the BiGyM upgrade, confirming that the adopted design choices are well suited to access divertor–relevant regimes and providing quantitative guidance for the finalisation of the machine layout and operational strategy.
References
[1] A.Uccello et al (2023) Front. Phys. 11, 1108175
[2] P.Guittienne et al (2021) Plasma Sources Sci. Technol. 30 075023
[3] I.Furno et al (2017) EPJ Web Conf. 157, 03014
[4] S.Wiesen et al (2015) J. Nucl. Materials 463:480–484

Speaker: Irene CASIRAGHI

Casiraghi_Scionti.pptx

16:45 → 18:30 plasma wall interaction & spectroscopic diagnostics

Conveners: Andrea UCCELLO (Consiglio Nazionale delle Ricerche, Istituto per la Scienza e Tecnologia dei Plasmi (CNR-ISTP)), Giorgio DILECCE (CNR - ISTP)

17:00 → 17:15 Helicon Wave Propagation for the BiGyM Linear Device

One of the main challenges in magnetically confined fusion research is the development of plasma-facing materials able to withstand the harsh environment of long-term plasma exposure. Linear plasma devices are widely used to address this issue. GyM [1] is one such device, capable of generating steady-state plasmas with electron temperatures up to 15 eV, densities in the range of 10¹⁵–10¹⁷ m⁻³, and ion fluxes up to 10²¹ m⁻²s⁻¹. GyM is currently being upgraded to BiGyM within the framework of the NEFERTARI project, funded by NextGenerationEU. The upgrade introduces a pair of helicon wave-generating birdcage radiofrequency (RF) antennas [2] to extend the operational range toward divertor-relevant plasmas with densities up to 10¹⁹ m⁻³ and ion fluxes of 10²³ m⁻²s⁻¹.
The work carried out in this project focused on validating the initial design choices taken for the device by investigating antennas performance and wave propagation. The figure of merit for this scope was the RF power density deposited by the wave, since maximizing such quantity represents the optimal energy transfer to the plasma.
A full 3D finite element model was developed using COMSOL [3], which reproduces the electromagnetic behaviour of the device and allows to study the propagation of the helicon waves generated by the antennas in a plasma. The model sensitivity to key physical parameters (neutral pressure and temperature, and plasma temperature) was tested and the effect of different antenna phasing on the helicon wave patterns was investigated in a hydrogen plasma. A set of different vessel geometries was investigated, each with a specific magnetic field profile, reaching plateau values of 18 mT. The results of this analysis allowed to identify the configuration that maximises the power deposition at the sample position and the best antennas phasing. The maximum power density value of about 105 W/m³ can be reached at the sample, up to two orders of magnitude higher than in the least favourable configurations.
The modelling activity supported the validation of the optimal design for BiGyM and offers a valuable tool for assessing antennas performances and serves as a reference on plasma operating conditions.

Speaker: Jimmy SCIONTI (Consiglio Nazionale delle Ricerche)

17:15 → 17:30 Laser ablation modeling and experimental activities supporting the implementation of an in-situ LIBS diagnostics for fusion-relevant plasma-material interaction studies

Laser-Induced Breakdown Spectroscopy (LIBS) is a versatile laser-based diagnostic technique that enables rapid elemental and isotopic characterization of materials through the analysis of optical emission from a laser-induced plasma. Thanks to its intrinsic features – such as remote detection, the absence of sample preparation, and the capability to work under harsh environmental conditions (including the presence of plasma and magnetic field) – LIBS is considered a promising diagnostics tool for in-situ monitoring of Plasma Facing Components (PFCs) in magnetic confinement fusion devices. In particular, it offers significant potential for investigating impurity deposition and hydrogen isotope retention, which are critical issues for the development of future fusion reactors.
This presentation summarizes the Ph.D. research activities carried out within the framework of the NEFERTARI project, a national initiative funded by Next Generation EU aimed at upgrading laboratories and experimental infrastructures for nuclear fusion research in Padova, Bari, and Milano. The doctoral project focused on preparatory activities aimed at supporting the implementation of an in-situ LIBS diagnostic on the upgraded BiGyM Linear Plasma Device (LPD), located at CNR-ISTP Milano.
A preliminary diagnostic layout was defined based on a literature review of LIBS applications in fusion environments and on sensitivity analyses performed on simple LIBS spectra. A picosecond Nd:YAG laser source and a compact high-resolution spectrometer (Isoplane 320 monochromator coupled to a PI-MAX 4 ICCD camera, Princeton Instruments) were identified as suitable components for a LIBS system mainly devoted to fuel retention studies. In addition, a conceptual optical path for coupling the laser system to the LPD was designed.
A major contribution of this work was the development of a numerical model of the laser ablation process, conceived as a predictive and interpretative tool for LIBS applications. The modeling activity, implemented using COMSOL Multiphysics, initially focused on the nanosecond pulse regime, which is widely adopted in fusion-related studies. The model describes laser energy deposition, heat transfer, phase transitions, and material removal mechanisms, enabling the prediction of ablation crater depth and diameter, as well as the temporal evolution of temperature within the target. The framework was subsequently extended to the picosecond regime through the implementation of a Two-Temperature Model, allowing separate treatment of electron and lattice subsystems and providing insight into non-equilibrium heating dynamics. Model predictions for both regimes were validated against dedicated laser irradiation experiments on tungsten and silicon, showing good agreement in terms of crater morphology and dimensions.
In addition, in-situ LIBS experiments for short-term deuterium retention measurements were performed on the PSI-2 LPD during a visiting period at the Forschungszentrum Jülich. These measurements provided practical insight into hydrogen isotope detection in fusion-relevant materials and enabled the extraction of short-term retention data and their temporal evolution for tungsten and tantalum, the latter being a potential alternative to tungsten for PFC applications. Furthermore, results from Nulcear Reaction Analysis (NRA) measurements, providing absolute concentration values and depth profiles for the two materials, are also reported.
Overall, the results discussed in this work provide a consistent framework that integrates diagnostic design, numerical modeling, and experimental validation. This combined approach supports the future implementation of an in-situ LIBS system on BiGyM and contributes to the development of a reliable diagnostic tool for plasma–material interaction studies under fusion-relevant conditions.

Speaker: Stefano CIPELLI (University of Padua/Consorzio RFX)

Nefertari FinalWorkshop Cipelli.pptx

17:30 → 17:45 WP9 - Development of LIBS Methodologies for Fusion-Relevant Materials Analysis

The primary aim of this WP was to reduce the spectral bandwidth of laser-induced emission in order to reliably detect and separate the hydrogen (Hα) and deuterium (Dα) lines using Laser-Induced Breakdown Spectroscopy (LIBS), with particular relevance to plasma–material interaction studies in fusion research. To achieve this goal, a LIBS laboratory was established from the ground up, including ultrafast lasers, ICCD-based spectrographs, vacuum and discharge systems, and diagnostics, and the methodology was progressively optimized as instrumentation became available.
A semi-qualitative investigation of nanosecond (ns), picosecond (ps), and femtosecond (fs) LIBS parameters demonstrated that spectral resolution is not governed solely by signal intensity but critically by the temporal evolution of the plasma.
The crater study, performed using optical profilometry, was a key component of this work and addressed a gap in the literature where LIBS spectral analysis and crater morphology are rarely studied simultaneously. Crater depth and width evolution on tungsten and molybdenum showed that ultrashort pulses produce well-defined, reproducible craters with minimal melting and redeposition. We have explored depths up to ~16 µm, well beyond the few-micrometer range commonly reported for fuel retention.
The discharge-assisted LIBS study demonstrated that an externally applied electrical discharge can decouple ablation from excitation. The discharge sustained excitation long after the LIBS plume decayed, allowing signal integration over hundreds of microseconds. This approach mitigated signal degradation over multiple laser shots and enabled stable detection even when the LIBS-only signal vanished at long delays.
A dedicated study of discharge characteristics and deuterium loading showed that a low-pressure two-electrode discharge can sputter electrode material and and trap deuterium onto a nearby molybdenum surface, producing laboratory-prepared samples. Electrical characterization confirmed stable discharge operation, and LIBS analysis verified the presence of hydrogen and deuterium emissions.
Finally, the detection and separation of Hα and Dα lines was achieved using optimized fs-LIBS conditions. Time-resolved spectra showed clear separation of the two lines at early delays, with reduced bandwidth compared to ns and ps cases. Overall, this work establishes a complete experimental framework spanning LIBS optimization, crater morphology, discharge assistance, and sample preparation that demonstrates a viable pathway toward high-resolution, depth-resolved detection of hydrogen isotopes relevant to fusion plasma diagnostics.

References
1. Hussain, A., Aceto, D., Ambrico, P. F., & Dilecce, G. (2025). Characteristics of glow-discharge LIBS in a rarefied environment. Plasma Physics and Controlled Fusion, 67(10), 105014. https://doi.org/10.1088/1361-6587/ae0cfe;
2. Cipelli, S., Aceto, D., Ambrico, P. F., Casiraghi, I., Cremona, A., De Pascale, O., Dilecce, G., Hussain, A., Laguardia, L., Pedroni, M., Ricci, D., Ripamonti, D., Scionti, J., & Uccello, A. (2025). Nanosecond laser ablation modeling of silicon and tungsten as support activity for LIBS diagnostic. Journal of Nuclear Materials, 156315. https://doi.org/https://doi.org/10.1016/j.jnucmat.2025.156315
3. Hussain, A, D. Aceto, P. F. Ambrico, G. Dilecce; (2025). Laser Induced Breakdown Spectroscopy from
ns to fs laser pulses for the detection of deuterium in fusion plasma walls[Poster]. International Conference on Phenomena in Ionized Gases 36th Edition; Aix-en-Provence France;
4. Hussain, A, D. Aceto, P. F. Ambrico, G. Dilecce., (2024). Discharge-assisted LIBS for the analysis of hydrogen isotopes content in tungsten samples [Poster]. Low-Temperature Plasma Diagnostic Conference 2024, Czech Republic;
5. Hussain, A, D. Aceto, P. F. Ambrico, G. Dilecce., (2024). Enhanced LIBS signal with small linewidth by electrical discharge assistance for application to hydrogen and deuterium line separation in plasma-surface interaction studies [Poster]. Third Futuro INAREA Symposium 2024, Bari, Italy;
6. Cipelli, S., Aceto, D., Ambrico, P. F., Cremona, A., De Pascale, O., Dilecce, G., Hussain, A., Laguardia, L., Ricci, D., & Uccello, A., (2024). Nanosecond laser ablation modeling using COMSOL Multiphysics as support activity for LIBS diagnostics [Poster]. FuseNet PhD Event 2024, Stuttgart.
7. Hussain, A., (2024). 61st Culham Plasma Physics Summer School, Culham Campus, Abingdon UK; http://www.culhamsummerschool.org.uk. 15/07/2024-25/07/2024.

Speaker: Arshad HUSSAIN (University of Padua/RFX Consortium)

Arshad_Nefertari_Presentation.pdf

Arshad_Nefertari_Presentation.pptx

17:45 → 18:00 WP9 - Plasma Sources and Optical Diagnostics

WP9 - Research and Development of optical plasma diagnostics and modelling for fusion
Plasma Sources and Optical Diagnostics
Domenico Aceto, Arshad Hussain, Paolo Francesco Ambrico, Giorgio Dilecce
CNR- ISTP sezione di Bari

Within the framework of the NEFERTARI project, a high-density plasma discharge prototype based on an Inverse Brush Cathode (IBC) Reflex configuration has been designed, installed, and experimentally characterized. The system operates in pulsed DC mode, with optional RF superposition, at pressures in the 0.01–0.1 Torr range. The discharge geometry consists of eight water-cooled cathodes arranged in opposing pairs around a central spherical anode, enabling a pronounced reflex effect that enhances ionization efficiency at low pressure.
Electrical characterization was performed through current–voltage measurements under different cathode configurations, clearly demonstrating the role of the reflex mechanism in sustaining high discharge currents even in weakly collisional regimes. Time-resolved Langmuir probe diagnostics, synchronized with the discharge pulse, were employed to measure electron density, electron temperature, and plasma potential. Electron densities follow the discharge current trend, while electron temperatures remain below 1 eV, consistent with a partially ionized, low-temperature plasma well suited for spectroscopic investigations.
RF superposition produces a substantial increase in plasma luminosity and electron density. Quantitative probe diagnostics in this regime are partially affected by RF-induced perturbations, for which mitigation strategies are currently under development.
Beyond hydrogen operation, laser-induced fluorescence (LIF) diagnostics were carried out on N₂ and N₂/O₂ discharges using laser instrumentation acquired within the project [1]. A pin-to-plate geometry operating at 100 Torr in pure nitrogen and a plate-to-plate configuration fed by air at atmospheric pressure were investigated, providing spatially resolved measurements of excited-state populations and collisional processes. These results yield insight into energy transfer mechanisms and plasma chemistry relevant to both spectroscopic studies and application-oriented research [2-9], and are further supported by comparison with numerical simulations.

[1]: L. Ibba et al 2025 Plasma Sources Sci. Technol. 34 105012, DOI 10.1088/1361-6595/ae0765
[2]: M. Ambrico et al 2025 J. Mater. Chem. A 14 4996-5006, DOI 10.1039/D5TA05024C
[3]: D. Aceto et al 2025 Chem. Biol. Technol. Agric. 12 151, DOI 10.1186/s40538-025-00865-0
[4]: M. Ambrico et al 2025 J. Phys. D: Appl. Phys. 58 125302, DOI 10.1088/1361-6463/ada44d
[5]: R. D’Orsi et al 2025 J. Phys. Mater. 8 045003, DOI 10.1088/2515-7639/adf94c
[6]: P.R. Rotondo et al 2025 Sci Rep 15 5536, DOI 10.1038/s41598-025-88369-7
[7]: D. Aceto et al, Frontiers in Low Temperature Plasma Diagnostics 2024 (FLTPD XV), 28/04-02/05/2024, Castle Liblice, Prague, Czech Republic, oral presentation: “Laser Diagnostics in an Atmospheric Pressure, Plane-to-Plane Nanosecond Pulsed Diffused Dielectric Barrier Discharge”.
[8]: D. Aceto et al, Europhysics Conference on the Atomic and Molecular Physics of Ionized Gases 2024 (ESCAMPIG XXVI), 9-13/07/2024, Brno, Czech Republic, poster presentation: “Atmospheric Pressure, Low -Temperature Plasma applications for decontamination of agrifood products”.
[9]: D. Aceto et al, International Conference on Phenomena in Ionized Gases 36th Edition (ICPIG 2025), 20-25/07/2025, Aix en Provence, France, poster presentation: “Plasma-Activated Fog treatments as sustainable protective tool in post-harvest”.

Speaker: Domenico ACETO (CNR - ISTP)

Aceto_WP9_final.pdf

Aceto_WP9_final.pptx

18:00 → 18:15 PIC model for negative ion source and plasma-divertor wall interaction

PICCOLO (PIC COde for LOw temperature plasma), a general-purpose suite code developed at CNR-ISTP-Bari in collaboration with ENEA-Frascati will be first presented. Two different simulation scenario will be shown, the first is the negative ion source SPIDER and the second the plasma-wall transition in the divertor region. Both simulations are two-dimensional in cartesian geometry. The plasma transport in the plane perpendicular to the magnetic filter field of SPIDER has been analyzed. It leads to important asymmetry and dis-honogeneity along the entrance of the extraction region [1,2]. Finally, PICCOLO has been used to self-consistently calculate the particle and heat flux along the single divertor monoblock taking into account the realistic geometry of the monoblock. The 2D domain extends along the toroidal direction y and the direction normal to an axisymmetric divertor z. The effects of the bulk collisions and of the electron surface emission (secondary and thermionic) has been analyzed. The ion impact energy and angle distribution is also calculate to better assess possible ion-induced erosion of the tungsten divertor wall.

[1] F. Taccogna, A. Panarese, A. De Tommaso, P. Minelli, F. Cichocki, Particle-in-Cell modeling of SPIDER negative ion source, ESCAMPIG XXVI, Brno, Czech Republic, July 9–13, 2024.
[2] F. Taccogna, P. Minelli, F. Cichocki, PICCOLO: a Particle-in-Cell code suite for low-temperature plasmas, XXXVI ICPIG, Aix-en-Provence, France, July 20-25, 2025.

Speaker: Francesco TACCOGNA (CNR)

Nefertari_FinalWorkshop_Taccogna.pdf

18:15 → 18:30 discussion - plasma wall interaction & spectroscopic diagnostics

Chair 1: Andrea Uccello
Chair 2: Giorgio Dilecce

18:30 → 19:30 contingency

19:30 → 22:30 Social Dinner

https://www.exforo.it/

Friday 27 March

08:30 → 09:00 Accoglienza - Welcome coffee

09:00 → 09:05 Benvenuto dell'Area territoriale della Ricerca del CNR di Padova

Speaker: Maria LOSURDO (CNR-ICMATE)

09:05 → 09:10 Introduzione alla giornata

Speaker: Stefano FABRIS (CNR-DSFTM)

09:10 → 09:35 Risultati del progetto NEFERTARI: Infrastruttura di ricerca sulla fusione potenziata con il PNRR

Speaker: Simone PERUZZO (CNR-ISTP)

09:35 → 09:50 Le Infrastrutture di Ricerca potenziate dal PNRR nel settore ESFRI ENERGY

Speaker: Michela VELLICO (OGS)

09:50 → 10:40 Business & Big Science: Public-Private Partnership nell’ambito dell’energia da fusione

Tavola rotonda con la partecipazione di:
- Diego Ruaro (De Pretto Industrie S.r.l.)
- Fabio Zanon (Eni S.p.A., Magnetic Fusion Initiatives)
- Giuseppe Taddia (OCEM Power Electronics)
- Enrico Maccallini (SAES Getters S.p.A.)
- Andrea Baratta (Simic S.p.A.)

moderatore: Piergiorgio Sonato (Consorzio RFX)

SAES GETTERS Presentation.pdf

10:40 → 11:30 Opportunità per le PMI: Tavola rotonda

Tavola Rotonda con la partecipazione di:
Stefano Miotto (Confindustria Veneto)
Filippo Mazzariol (Unioncamere Veneto)
Sergio Bobbo (CNR-ITC)
Olga De Pascale (CNR-ISTP)
Simone Peruzzo (CNR-ISTP)
Alessandra Canton (Consorzio RFX)

moderatore: Vanni Antoni (CNR-ISTP & Consorzio RFX)

11:30 → 13:00 Visita Tecnica: Tour guidato agli impianti sperimentali RFX-mod2 e NBTF

13:00 → 14:00 Networking Lunch: Connessioni tra ricercatori e aziende