5th IWC-HTS International Workshop on Cooling Systems for HTS Applications

26 Oct 2026, 08:30 → 29 Oct 2026, 22:05 Europe/Zurich

Waaier (University of Twente)

Patricia Tavares Coutinho Borges De Sousa (CERN), Srini Vanapalli (University of Twente), Hans van Oort (University of Twente)

It is our great pleasure to invite you to join us at the 5th International Workshop on Cooling Systems for HTS Applications (IWC-HTS 2026) at Enschede, The Netherlands. The IWC-HTS 2026 is co-sponsored by Cryogenics Society of Europe. The workshop aims to effectively exchange the latest research results with a focus on technology for high temperature superconducting systems. 

Set in the green campus of the University of Twente, the venue offers a unique combination of cutting-edge research facilities and a tranquil, inspiring environment. The campus provides modern conference spaces, networking areas, and a vibrant academic atmosphere that fosters collaboration and idea exchange.

Conference website: www.hts2026.com 

Chairpersons: 

Dr. Patricia Tavares Coutinho Borges De Sousa (CERN, Switzerland)

Prof. dr. Srini Vanapalli (University of Twente, The Netherlands)

Prof. dr. Hans van Oort (University of Twente, The Netherlands)

 

Monday 26 October

08:30 → 17:00 Technical Course: Introduction to AC losses in Superconductors

Lecturers: dr.ir. Ruben Keijzer, ir. Jurrie Bruggeman
In this short course we aim to introduce you to the rich field of superconductor AC loss. With the growing application of 2G ReBCO coated conductors in electrical machines, a solid understanding of AC loss mechanisms is vital for proper design of their cooling architecture.
The morning program consists of lectures covering the basics of superconductor AC loss in terms of physical mechanisms, measurement techniques and numerical modelling methods.
We will conclude the morning session with a tutorial on the numerical implementation of Brandt’s method to calculate AC loss and current distribution in ReBCO coated conductors.
In the afternoon, a hands-on experimental tutorial will allow you to apply this knowledge in our lab. You will conduct experiments related to measuring the properties of superconductors and you will learn how to set up an electrical AC loss measurement. During your time in our lab, past and present experiments conducted at the University of Twente are also on display with plenty of opportunity for discussion!
N.B. For the morning tutorial session it would be convenient if you bring your own laptop, with either Julia or Matlab installed.

Conveners: Jurrie Bruggeman, Dr Ruben Keijzer

Tuesday 27 October

09:00 → 09:05 Welcome

09:05 → 09:45 Plenary - Herman ten Kate

Convener: Prof. Hans van Oort (University of Twente)

09:05 Advances in High-Temperature Superconductors and their Application: Promises, Problems and Prospects

For over four decades, we have specialised in high-temperature superconductor (HTS) technology. The current-carrying capacity, manufacturability and practical performance of the conductors has increased significantly.
A variety of materials were considered for use as practical conductors. However, the current focus of R&D and industrial efforts is primarily, although not exclusively, on ReBCO tape conductors for the fabrication of cables and coils. These include high-field magnet facilities, magnets for fusion devices, power transmission, electric motors, magnetic levitation and medical technologies.
While current tape technology may be adequate for low-energy stationary devices, more development is necessary for larger-scale high-energy devices and varying field magnets, which require cables and large coils. It is essential that this technology evolves to ensure stable and reliable operation, initially in demonstrator models and subsequently in commercial devices.
There are still several challenges to be addressed, including manufacturing costs, material brittleness, electrical and mechanical anisotropy, AC loss, quench protection, and cooling requirements at 20 - 40 K level.
The promises, problems and prospects of HTS technology in terms of achieving a more efficient and sustainable future are addressed.

Speaker: Herman ten kate

09:45 → 10:35 Oral Session - Cryogenics for Large Scale Applications

Session chair: Srini Vanapalli

Convener: Vicente Climente-Alarcon (United Kingdom Atomic Energy Authority - UKAEA)

09:45 High-Temperature Superconductivity and Deep Cryogenics: A Relationship with a Future

The discovery of high-temperature superconductors in 1986 seemed to herald the end of the era of large cryogenic systems. Phase transition temperatures of up to 138 K were achieved in ceramic materials within a short period of time. Superconductivity at room temperature seemed within reach. However, further success proved much more difficult than expected. The material class of hydrides, for example, requires pressures far too high (> 100 GPa) for any practical application, and the brittleness of ceramic superconductors initially posed major challenges for cable manufacturers. For many years, HTS conductors existed as niche demonstration projects, initially in areas such as current limiters, generators, and motors. In 2014, a 1-kilometer-long HTS cable was integrated into the power grid of the city of Essen, Germany, on a trial basis for the first and for a limited time.
The complex process of manufacturing HTS cables has now been mastered, resulting in a dramatic fall in production costs. At the same time, the quest for higher magnetic fields pushed conventional superconducting technology towards its limits, creating new opportunities. Among other achievements, this led to the development of HTS magnets cooled with liquid helium — well below their phase transition temperature. Stable magnetic fields of up to 45 tesla can now be generated with very compact magnets. This has led to significant progress in areas such as fusion technology, which was once considered highly futuristic.
The increasing technical maturity of HTS technology does not render cryogenics obsolete; rather, it creates new opportunities and demands for cryogenic systems. This presentation will discuss the cryogenic challenges, cooling concepts, and practical implementation of modern HTS applications. Examples from the fields of power transmission, fusion technology, particle accelerators, and other industrial systems illustrate how advances in superconductivity are driving renewed demand for innovative cryogenic solutions.

Speaker: Lutz Decker (Linde Kryotechnik AG)

10:05 A Conduction Cooled modular testbed for Coated Conductors and High Field Magnets

Princeton Plasma Physics Laboratory (PPPL) is a DOE national laboratory focused on plasma physics and nuclear fusion science. Our primary mission is research into and development of fusion as an energy source. PPPL recently developed a REBCO coated conductor continuous in-field characterization system and tested a large warm bore conduction cooled Nb3Sn model coil capable of generating 6 T in a liquid cryogen free modular testbed. PPPL is also building a 900 mm warm bore conduction-cooled superconducting magnet to support a new laboratory search for dark matter with a small scale experiment - Princeton Axion Search (PXS). Fundamental understanding of electro-thermal-mechanical properties of coated conductor, and its deployment in high current HTS cable and coil assembly for high field HTS magnets is critical for thermal and mechanical management to avoid quench damage and screening current induced stress failure. The design and fabrication for a cryocooler-based modular testbed will be presented and the design is anticipated to achieve first and second stage temperatures of 44 K and 4.5 K respectively. The conduction cooled modular testbed is being commissioned to validate coil test capabilities and thermal links. Modeling results of HTS insert coil cooling scenarios in the conduction cooling system including cooldown, current ramp and quenching will be discussed.

Speaker: Yuhu Zhai (Princeton Plasma Physics Laboratory)

10:20 On the use of a hyperconducting centre solenoid for spherical tokamaks

Tokamaks rely upon a centre solenoid to initiate and warm up the plasma at the beginning of each pulse [1]. A conventional centre solenoid consisting of hollow copper conductors and insulated with epoxy resin-impregnated glass and kapton tape was used in JET [2]. In the larger ITER, however, it was decided that only a superconducting coil could fulfil the flux requirements. NbTi cooled down to the boiling temperature of helium is used in this case [3]. The introduction of Nb3Sn and/or high temperature superconductors appear as the only viable options for the even bigger DEMO [4]. Nevertheless, cryogenically cooled materials that exhibit conventional conduction behaviour could still be a feasible solution for smaller devices that promise to deliver a simpler design for plasma confinement and heating. This is the case of the spherical tokamaks, where the bootstrap current greatly contributes to plasma heating, and hence less externally applied flux variation is needed. Moreover, in this kind of devices the leaner centre pylon limits the neutron shielding options, and neutron triggered effects would reduce the endurance of delicate materials such as HTS. In this sense, this contribution will present an optimisation procedure, from the point of view of the purity of the material, of conventional, cryogenically cooled centre solenoids. It will show how higher purities do not always imply a reduction in losses [5]. The effect of neutron radiation will also be accounted for [6]. Finally, a simple method to connect current feeders to the centre solenoid will also be presented.

[1] P. Rutherford, “The Tokamak: 1955-80,” Nuclear Fusion, vol. 20, no. 9, pp. 1086-1092, 1980.
[2] J. R. Last, D. Cacaut, A. P. Pratt, J. C. Rauch, P. J. Ferry, U. Arensmann and A. Alvarez, “Poloidal coils and transformer core for JET - Design and manufacture,” IEEE Transactions on Magnetics, vol. 17, no. 5, pp. 1923-1926, 1981.
[3] B. Lim, F. Simon, Y. Ilyin, C. Y. Gung, J. Smith, Y. H. Hsu, C. Luongo, C. Jong and N. Mitchell, “Design of the ITER PF coils,” IEEE Transactions on Applied Superconductivity, vol. 21, no. 3, pp. 1918-1921, June 2011.
[4] M. Kumar, K. Sedlak, X. Sarasola and P. Bruzzone, “Preliminary design of DEMO PF coils based on EU DEMO 2018 baseline,” IEEE Transactions on Applied Superconductivity, vol. 30, no. 4, p. 4201505, June 2020.
[5] H. Zhang, A. C. Smith, M. F. Iacchetti, P. M. Tuohy, A.-V. Rusu, S. M. Harrison and V. Climente-Alarcon, “Optimizing loss performance in aluminum litz wires for cryogenic electrical machines,” IEEE Transactions on Energy Conversion, vol. 40, no. 3, pp. 2399 - 2409, September 2025.
[6] H. R. Brager, “Effects of neutron radiation to 63 dpa on the properties of various commercial copper alloys,” Westinghouse Hanford Company, 1986.

Speaker: Vicente Climente-Alarcon (United Kingdom Atomic Energy Authority - UKAEA)

10:35 → 11:10 Coffee Break

11:10 → 11:50 Plenary - Markus Mueller

Convener: Prof. Srini Vanapalli (University of Twente)

11:10 SuperMachine – a platform modular electrical machine for energy and transport applications

Electrification of energy, aviation and shipping requires lightweight, highly efficient electrical machines. Conventional permanent-magnet machines are difficult to scale to multi-megawatt wind systems while maintaining low mass, or to the power densities required for transport. The SuperMachine concept aligns the machine structure with the benefits of HTS materials and provides a highly modular architecture. This presentation covers experimental validation, modular cooling options and design studies for wind, aerospace and marine applications.

Speaker: Markus Mueller (The University of Edinburgh)

11:50 → 12:20 Oral Session - HTS Cable Developments

Session chair: Hans van Oort

Convener: Aya SBAI

11:50 Electromagnetic Design and Mechanical Evaluation of a 15 T High-Temperature Superconducting Racetrack Magnet

REBCO coated conductors are regarded as an enabling material for next-generation high-field magnets due to their high current-carrying capacity at elevated fields and temperatures. The development of compact high-field HTS magnets has become increasingly important across a variety of scientific and technological applications. Among different coil configurations, the racetrack geometry is particularly advantageous for generating a long and straight uniform field region, making it a natural fit for accelerator facilities, particularly superconducting dipoles (bending magnets) and insertion devices such as wigglers and undulators.
This paper presents a comprehensive design of a 15 T REBCO racetrack magnet. The magnet is designed to operate at 10 K, with a bending radius of 6 mm and a straight-section length of 50 mm, wound using 4-mm-wide REBCO tapes from Shanghai Superconductor Technology Co. A genetic algorithm (GA) is adopted for electromagnetic optimization to minimize tape consumption, with the number of double pancakes, turns per double pancake, and operating current as optimization variables. The target central field is 15 T. The optimized design consists of ten double pancakes with 400 turns each and operates at 200 A.
A systematic stress analysis is also performed, accounting for winding tension, thermal stress during cooldown, and Lorentz forces during energization. The results show that the maximum hoop stress reaches 430 MPa and is concentrated in the curved end regions, which remains below the 600 MPa tensile limit of the REBCO tape.
Based on the validated electromagnetic and mechanical designs, a prototype model coil is currently under fabrication. The winding is impregnated with solder via vacuum pressure impregnation (VPI) to ensure good inter-turn thermal and electrical conductivity while improving the overall mechanical rigidity. The magnet is conduction-cooled by a cryocooler, eliminating the need for liquid helium and simplifying the cryogenic system. Subsequent testing of the model coil will be carried out to verify the design methodology and validate the stress analysis, providing a technical reference for future high-field HTS magnet development.

Speakers: Mr Yuan Cheng (Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences), Mr Zhanguo Zong (Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences)

12:05 Toward design and optimization tools for high-temperature superconducting cable terminations

High-temperature superconducting (HTS) cables are promising candidates for compact and efficient high-power electrical transmission, owing to their high current-carrying capability and negligible ohmic losses under superconducting operating conditions. However, in applications involving relatively short cable lengths, such as urban power links, railway infrastructures, or embedded electrical systems, the relative contribution of the terminations to the overall thermal budget can become particularly significant. Reducing the heat load associated with HTS cable terminations is therefore a key challenge for improving the efficiency, compactness, and practical relevance of such systems.

This work addresses the steady-state thermo-electrical design problem of HTS cable terminations, which provide the electrical and thermal transition between the ambient-temperature power interface and the cryogenic cable core. Three representative architectures reported in the literature are reviewed and compared: conduction-dominated terminations, terminations cooled by natural convection, and terminations assisted by forced convection. A one-dimensional modelling framework is introduced for the resistive current lead, accounting for axial heat conduction, Joule heating, and, when relevant, convective heat exchange with the cryogenic fluid.

The comparison clearly shows that the cooling mode has a first-order impact on the thermal performance of the termination. For a representative nominal current of 2 kA, the estimated heat load at the cold end decreases from about 90 W for a conduction-dominated design to 39.4 W with natural convection and 16 W with forced convection. While forced convection offers the most effective heat extraction and may enable more compact designs, its benefit must be assessed at system level by including the additional losses, complexity, and integration constraints associated with auxiliary cooling equipment.

The proposed analysis provides a first benchmark for the design of efficient HTS cable terminations and represents an initial step toward a coupled thermo-electrical optimization tool. Future work will extend the model toward two- and three-dimensional multiphysics numerical validation, before progressing in the longer term to experimental assessment on a prototype termination. This will support the development of compact, low-loss and system-efficient terminations for practical HTS cable applications.

Speaker: Aya SBAI (Université de Lorraine, GREEN)

12:20 → 13:45 Lunch

13:45 → 14:25 Plenary - Tabea Arndt

Convener: Patricia Tavares Coutinho Borges De Sousa (CERN)

13:45 Cooling and operating stationary and rotating superconducting arrangements: concepts of the past, special requirements, and recent developments

Historically and even today for selected applications, superconducting coils have been cooled by liquid helium pool cooling. The technical viability and business case in magnets and power applications has been widely influenced by the operating conditions and the available cooling devices. HTS have simplified cryogenic measures and considerably extended the devices’ suitable power range. For stationary and rotating applications, specific requirements pose additional challenges for cooling concepts. However, current trends in magnets and rotating machines may enable new concepts. This presentation will give an overview of the historical basis, special aspects, the changes, and new prospects.

Speaker: Prof. Tabea Arndt (KIT)

14:25 → 15:30 Oral Session - Novel Cryogenic and HTS Technologies I

Session chair: TBD

14:25 Integrating Liquid Hydrogen for Advanced Cryogenic Cooling of High-Temperature Superconducting Devices

Interest in high-temperature superconducting (HTS) technologies is surging across fusion energy, large electric transport, data centers, and electric utilities due to their unmatched power density. Notably, liquid hydrogen (LH2) platforms simplify HTS integration by utilizing LH2 at 20 K as an effective cryogenic heat sink. However, the advancement of these technologies is heavily constrained by safety concerns and a scarcity of specialized, capital-intensive research facilities.
To accelerate progress, validate early designs, and de-risk prototype propulsion and power systems, collaborative development is essential. The Center for Advanced Power Systems (CAPS) and the FAMU-FSU College of Engineering have addressed this infrastructure gap by establishing advanced testbeds for HTS power distribution, cryogenic electrical insulation, fluid circulation, and AC loss measurement at LH2-relevant temperatures. Recent innovations at CAPS include novel heat exchangers, optimized cryogenic gas mixtures for enhanced heat transfer, and fully integrated cryogenic platforms. This presentation outlines these unique capabilities, highlights successful collaborative milestones, and invites new partnerships to maximize the impact of CAPS's research infrastructure.

Speaker: Sastry Pamidi (FAMU-FSU College of Engineering & The Center for Advanced Power Systems)

14:45 Development and Performance of a High-Capacity Closed-Cycle 1 K Cryostat for Low-Temperature Characterization of Superconducting Materials

A high-capacity closed-cycle 1 K cryostat based on a capillary Joule–Thomson (J–T) expansion stage is developed and experimentally characterized for low-temperature physical property measurements of superconducting detectors. The cryostat achieves a base temperature of 1.37 K and provides a cooling power of approximately 30 mW at 1.54 K. By employing a lower-impedance capillary, the cooling power can be increased up to 110 mW, at the expense of a moderate increase in the base temperature. The steady-state cooling performance is analyzed using an enthalpy-based thermodynamic model that accounts for both latent and sensible heat contributions of helium in different operating regimes. The cryostat also exhibits excellent temperature stability, with root-mean-square temperature fluctuations below 3.3 mK under typical thermal loads, satisfying the requirements for precision low-temperature material characterization. The demonstrated high cooling capacity, stable operation, and clear performance scaling provide practical design guidelines for capillary-based J–T cryostats targeting superconducting detector development and related cryogenic measurement applications.

Speaker: Prof. Cheng Shao

15:00 Heat pipe to interconnect cryogenic cooling circuits in a nuclear fusion machine

Viable nuclear fusion reactors will need to gather in a constrained space a wide variety of elements related to the fuel cycle, and plasma initiation, shaping, and positioning, amongst others. Tokamaks rely upon several sets of coils for plasma control [1]. The large currents circulating through those magnets make the use of superconductors advantageous. For practical purposes, superconductors offer no electrical resistance under constant current conditions; however, this assertion does not hold when current, magnetic field, or both, vary. In a Tokamak, toroidal field coils operate at nearly constant condition to provide a circumferential containment field, whereas the poloidal field ones must accommodate some pulsing mode to exerting its function of plasma initiation, shaping, and control [2]. These dissimilar functions and related performances are translated into different sets of requirements for their corresponding cryogenic systems. Hence, the common approach has been to design several independent cryogenic circuits [3]. In this regard, this contribution will present a cryogenic thermal bridge for connecting the cryogenic circuit of poloidal field coils to the cryogen return of the toroidal field ones. The thermal bridge would be constituted of copper heat pipes filled with a small quantity of either hydrogen (protium, deuterium), neon, or a mixture of them, which suffer a phase change around the expected temperature of operation of the HTS magnets (20 K – 30 K) [4]. In the proposed configuration, those heat pipes act as thermal diodes, evacuating the extra heat produced in the transient operation of the poloidal field coils to the cryogen return of the constant operated toroidal field ones, while preventing the heat flow in the contrary sense. This would increase the pulsing duty cycle of the poloidal field coils while saving space, especially scarce in locations around the inboard side of the vacuum vessel.

Speaker: Dr Vicente Climente-Alarcon (United Kingdom Atomic Energy Authority - UKAEA)

15:15 Turbomachinery-based cooling systems for HTS applications

Turbomachinery based cooling systems have advantages compared to other cooling systems in terms of low maintenance due to the oil-free gas bearing, low micro-vibration emission as they are continuous flow machines with well-balanced rotor, and the low specific energy consumption (W per W of cooling) due to their high efficiency. In a first concept, they are applied as turbo compressor and turbo expander in Reverse Turbo-Brayton (RTB) cryocoolers. The load heat exchanger (i.e. the cold head) of RTB cryocoolers can be mechanically connected to the HTS as for any other cryocooler. In a second concept, if a central cryo plant is available, i.e. if cold temperatures are already generated with a separate cryocooler, turbo compressors can distribute the cooling capacity via circulating cold helium (or other gases) to the HTS location. The gas-bearing turbo compressor operates as a cold compressor or a cryo fan. Again, at the application, a load heat exchanger can mechanically connect to the HTS or the helium can directly cool the HTS. Celeroton’s gas bearing and motor/generator technology allows for operation of the turbomachinery fully immersed in the cold zone, without requiring a flanged solution and therefore giving more flexibility to the cold box design and allowing for higher package density in the cold box.

Speaker: Patrik Fröhlich

15:30 → 16:00 Break

16:00 → 17:05 Oral Session - Novel Cryogenic and HTS Technologies II

Session chair: Yuhu Zhai

Convener: Yuhu Zhai (Princeton Plasma Physics Laboratory)

16:00 Role of Cryogenics in Superconducting RF (SRF Technology

Superconductivity plays a significant role in modern high-energy accelerators as it enables:

• High field magnets for bending, focusing, and wiggling charged particle beams
• High field magnets in large detectors for particle identification from colliders
• Superconducting RF cavities for charged particle beam acceleration

In this talk I will give a briefely describe the role of Cryogenics in SRF technology.

Speaker: Shrikant Pattalwar (UKRI- STFC Daresbury Laboratory)

16:20 Numerical Study of AC Loss in Fast-Ramping REBCO Coils with Micro-Filamentary Tape for Magnetic Refrigeration

Magnetic refrigeration and hydrogen liquefaction based on the active magnetic regenerator cycle require the applied field to be ramped up and down repeatedly. In a superconducting drive coil the resulting AC loss is dissipated directly into the cryogenic environment, so it competes with the useful cooling power of the device and sets a practical ceiling on the achievable cycle rate. Reducing this loss is therefore a prerequisite for compact, fast-cycling systems.

We report a numerical evaluation of the AC loss of REBCO coils wound from micro-filamentary coated conductor. The conductor is assumed to be processed by a fabrication route proposed by the present authors, which subdivides the tape into narrow filaments while maintaining a high inter-filament resistance. Coils operating at 20 K and generating up to 5 T are analysed using a three-dimensional electromagnetic model that resolves the individual filaments together with the resistive paths between them, so that both the hysteretic and the inter-filament coupling contributions to the total loss are obtained.

Calculations are carried out for filament numbers up to N = 100 and for several winding configurations. The dependence of the total loss on these parameters, the relative weight of the two loss mechanisms, and the resulting implications for the thermal load budget of the cryocooler are discussed.

Speaker: Haruumi Yamamoto (National Institute for Materials Science)

16:35 Producing neon from liquid-hydrogen cold energy to expand the usable inventory as coolant for HTS applications

Below the 77 K of liquid nitrogen, the practical liquid-cryogen candidates are essentially three, namely helium, hydrogen, and neon. Among them neon is distinctive. It liquefies near 27 K, possesses an exceptionally high volumetric latent heat, about forty times that of helium and three times that of hydrogen, and, as an inert noble gas, is non-flammable and does not embrittle materials. It avoids the explosion-proofing and material precautions that hydrogen demands, a practical advantage for high-temperature-superconductor (HTS) cooling.
Usable neon, however, is scarce. The atmosphere is its only terrestrial reservoir (~65 billion tonnes), yet at ~18 ppm neon is recovered only as a trace by-product of cryogenic air separation run mainly for bulk oxygen, nitrogen and argon. Global production is just a few hundred tonnes per year, a negligible fraction of the reservoir. Conventional liquefaction also depends on energy-intensive refrigerators with helium.
We examine the significance and feasibility of producing neon from the cold energy released when liquid hydrogen (LH₂) is regasified. Heat exchange with LH₂ can liquefy and purify neon without a helium refrigerator, converting otherwise-wasted cold into product. Thermophysical and energy-balance considerations indicate the cold is abundant relative to demand. The true constraint is the dilute air feedstock. As hydrogen infrastructure expands, such a route could progressively enlarge the neon inventory humanity can practically use, helping enable wider HTS deployment.

Speaker: Shinnosuke Matsunaga (National Institute of Technology, Gifu College)

16:50 Effect of temperature-gradient orientation on dissipative work in a tandem active magnetic regenerator

Tandem active magnetic regenerator (AMR) configurations, in which two AMR beds are magnetized and demagnetized in antiphase, are attractive because the magnetic forces acting on the beds largely cancel each other and the mechanical work required to drive the beds is reduced. In our previous force-based evaluation, however, the achieved reduction of the magnetic work was smaller than that expected from ideal cancellation. The work that remains consists of a reversible contribution associated with the temperature difference between the upper and lower beds and a dissipative contribution that cannot be recovered. This study focuses on the latter, hereafter referred to as the dissipative work, and identifies the factors that govern it. Under the idealized assumptions of isothermal magnetization and a spatially uniform bed temperature, the dissipative work is governed by the asymmetry of the axial magnetic field gradient experienced by the two beds over one stroke. We show that it becomes essentially zero if the field gradient varies linearly along the axial coordinate and its average over the entire bed length vanishes at both stroke ends. This condition is no longer sufficient once adiabatic magnetization and a realistic bed temperature gradient are taken into account. When the temperature gradient is parallel to the direction of bed motion, a substantial fraction of the input work remains dissipative. We hypothesize that this arises from the asymmetry of the magnetization caused by the local temperature distribution during the field change. To examine this, the temperature gradient was reoriented along the radial direction of the bed, so that the cross-sectionally averaged temperature becomes uniform over the whole bed length. The calculated dissipative work fraction then decreased substantially, supporting the proposed mechanism and indicating that the orientation of the temperature gradient relative to the field-gradient axis is a key design parameter for tandem AMR systems.

Speaker: Mr Tsuyoshi Shirai (National Institute for Materials Science)

18:00 → 21:00 Social Dinner - Twente FC

Wednesday 28 October

07:00 → 08:00 Fun Run

08:50 → 08:55 Welcome

08:55 → 09:35 Plenary - Prof. Nakamura

Convener: Marc Dhallé (University of Twente)

08:55 Current Status and Prospects of Liquid-Hydrogen-Cooled High-Temperature Superconducting Rotating Machines

Liquid hydrogen serves as an excellent medium for transporting hydrogen, a clean energy source for the next generation. Also, its atmospheric boiling point (20 K) is well-suited to the operating environment of high-temperature superconducting equipment; thus, a synergistic effect between the liquid hydrogen—acting as both an energy source and a coolant—and the superconducting equipment enables the realization of highly efficient systems. This presentation provides an overview of liquid-hydrogen-cooled high-temperature superconducting rotating machines, covering their fundamental concepts, applications such as in aircraft and liquid hydrogen pumps, and future prospects.

Speaker: Taketsune Nakamura

09:35 → 10:35 Oral Session - Big Science & Protection

Session chair: TBD

Convener: Prof. Hans van Oort (University of Twente)

09:35 Thermo-economic optimization of cooling systems for nested HTS magnets in the FCC-ee short straight sections

The HTS4 project, part of the CHART framework and the FCC Feasibility Study, investigates energy-efficient nested high-temperature superconducting (HTS) magnet systems for the FCC-ee short straight sections (SSS). Replacing selected normal-conducting magnets with nested ReBCO-based variants can reduce electricity consumption through two mechanisms: elimination of ohmic magnet losses and an increased dipole filling factor, which lowers the synchrotron-radiation power. The increased filling factor may also reduce the required RF voltage and, consequently, the scale and cost of the RF system.

We present a coupled electromagnetic, thermal, and economic optimization workflow for determining the preferred operating temperature and cooling-system architecture of the nested HTS magnets. Electromagnetic feasibility and field quality are evaluated using a two-dimensional finite-element model. For each configuration, the current-sharing temperature is calculated from the J_c scaling law. The cold heat load is determined using a component-level model that includes multilayer-insulation radiation, structural conduction, beam-induced heating, parasitic loads, and powering-related losses.

For conduction-cooled configurations, cryocooler cooling power and electrical input power are calculated using fitted manufacturer load-map data within the experimentally characterized operating range. The model also accounts for the thermal load of inactive coldheads in redundant configurations and constrains both the heat lift and electrical input per active coldhead. Distributed cryocoolers are compared with distribution-line concepts supplied by centralized cryogenic plants, together with alternative magnet-powering schemes.

The analysis is applied to both the LCC and GHC magnet configurations, to quantify how their different electromagnetic and thermal requirements affect the preferred operating temperature, cooling architecture, cooler count, redundancy, conductor amount, and electrical input power. For the LCC configuration, the present baseline favors distributed conduction cooling at a cold-sink temperature of around 40-50 K. Comparison with the GHC configuration establishes how the magnet and layout requirements shift the preferred cooling concept and operating point. More generally, the study identifies the principal design and cost trade-offs for large-scale deployment of HTS magnets in the FCC-ee short straight sections and the conditions under which they could become competitive with the normal-conducting reference.

This work was performed under the auspices of and with support from the Swiss Accelerator Research and Technology (CHART) program (www.chart.ch).

Speaker: Jaap Kosse (PSI)

09:55 The Protection Paradox

One of the great advantages of High Temperature Superconductor (HTS) magnets is their high thermal stability. Yet many protection concepts envisioned for large magnets deliberately work against this property by improving normal-zone propagation through partial insulation, heaters, or other means. Better propagation may help distribute energy, but it also makes the coil itself less stable.

There is a second problem: when the protection function is built into the winding pack, it is difficult to validate it independently. Testing this type of protection means deliberately driving the magnet into precisely the condition it is meant to survive, putting the full coil at risk.

This talk argues for separating these two functions. The magnet should be optimised for stability, cooling, and recovery from disturbances, while fast and deliberately unstable behaviour is moved into a dedicated, independently testable protection component. The challenge then becomes a rather unusual one: can we build an HTS component that is very good at becoming resistive, quickly and reliably, when we ask it to?

Speaker: Dr Jeroen van Nugteren (Little Beast B.V.)

10:15 Implementation of new cooling methods and instrumentation development for HTS magnets in the CERN SM18 test facility

The SM18 superconducting magnet test facility has a long-standing history and large capacity for testing superconducting magnets for accelerators. Existing cooling capacity includes 1.9 K or 4.5 K helium bath cooling, as used in LHC and HL-LHC magnets, and helium gas cooling from 5 to 80 K, used for HTS magnet tests, mostly within the HFM program. For 2027, a new cryostat insert is in development to provide conduction cooling and helium channel cooling while the magnet remains in vacuum.
Another ongoing development is cold electronics, which aims to provide signal amplification and noise reduction from the measurements and could have a strong impact on instrumentation and diagnostics, including voltage, acoustic, magnetic, and quench antenna measurements. In this contribution, the advancement in test station cooling methods for HTS magnets, as well as the advancement in instrumentation and electronics, will be discussed.

Speaker: Gerard Willering (CERN)

10:35 → 11:05 Coffee Break

11:05 → 11:45 Plenary - Mariusz Wozniak

Convener: Herman ten kate

11:05 Protection of HTS CC Magnets: Strategies, Challenges, and the Role of Numerical Modelling

High-temperature superconducting (HTS) coated conductor (CC) magnets have the potential to reach high fields for accelerators, fusion devices, and user magnets, but protecting them against quench-induced damage remains a central obstacle to their deployment. Compared with low-temperature superconductors (LTS), HTS combine slow normal-zone propagation and high minimum quench energy. Passive and active normal zone propagation that serve LTS magnets well are largely ineffective for HTS. Whereas for LTS limiting quench voltage and temperature during quench are important, for HTS CC also superconductor-level stresses due to the risk of delamination and, for no-insulation (NI) coils, the redistribution of current, energy, and force density bring additional challenges.

This talk provides an overview of strategies for protecting HTS magnets. The stored magnetic energy can be distributed (propagated) within the magnet or removed (extracted) from it by active or passive means through the conductor, coupled coils, structures, or power source. NI coils receive attention: current redistribution lowers the current density in the quenched region but has the potential to dramatically increase thermo-mechanical stress in other places of the magnet, and this is often hard to predict and design against. Energy extraction, quench heaters, coupling-loss-induced quench (CLIQ), the recent Energy Shift with Coupling (ESC), and the intrinsic current sharing of NI and metal-insulation windings are compared.

A recurring theme for HTS protection is that the quench analysis demands coupled magneto-thermal-mechanical modelling and constrains conductor and magnet design from the outset. The talk highlights where numerical modelling is decisive and current STEAM framework software capabilities, as well as the need for HTS-specific additional capabilities. Various tools will be presented with their differences highlighted. The impact and relevance of quench detection and protection for the cooling and cryogenics of HTS magnets will also be discussed.

Speaker: Dr Mariusz Wozniak (CERN)

11:45 → 12:30 Oral Session - Superconducting Motors, Generators & Actuators

Session chair: TBD

Convener: Marc Dhallé (University of Twente)

11:45 Design, Optimization and Validation of Flux Pumps for 2G HTS Coil Excitation

The increasing demand for renewable electricity is driving the deployment of larger and more powerful offshore wind turbines. Electrical machines employing second generation high temperature superconducting (2G HTS) field windings offer the potential for high magnetic loading, increased torque density and reduced active mass. However, conventional conductive energization of these 2G HTS windings requires high current leads and electrical joints. This introduces heat into the cryogenic environment through thermal resistive losses $[P_{\mathrm{joint}}]$ as described in equation (1). Moreover, the higher currents $[I_{\mathrm{HTS}}]$ of 2G HTS conductors can result in substantial resistive losses at these electrical joints.
$$ P_{\mathrm{joint}} = I_{\mathrm{HTS}}^2R_{\mathrm{joint}}. \tag{1} $$ This work investigates flux pump systems for efficient, non contact energization of 2G HTS field windings. Two flux pump configurations; a rotary permanent magnet flux pump (PMFP) and a stationary travelling wave flux pump (TWFP) are designed, fabricated and experimentally evaluated. Finite element models developed in Ansys Maxwell are used to characterize the magnitude, spatial distribution and temporal waveform of the magnetic flux density in the HTS air gap. The PMFP produces a short unipolar magnetic-field pulse during each magnet passage, followed by a relatively long low-field interval. In contrast, the TWFP employs multiphase AC windings together with a DC bias winding to generate a continuous, sinusoidal unipolar travelling magnetic field $[B_y(x,t)]$ according to the equation (2). Here, $B_{\mathrm{dc}}$ and $B_{\mathrm{ac}}$ are the instantaneous magnetic flux densities resulting from the DC and the AC supply respectively. And in steady-state, the electric field introduced in the 2G HTS depends on this travelling magnetic wave and the vortex velocity of the 2G HTS according to Faradays electro-magnetic induction. $$ B_y(x,t) = B_{\mathrm{dc}} + B_{\mathrm{ac}}\cos(kx-\omega t). \tag{2} $$ Although the reference PMFP demonstrated better initial charging performance, the TWFP is selected for further optimization because its stationary construction eliminates mechanically rotating components near the cryogenic system and therefore offers greater mechanical simplicity and potential reliability. Preliminary experiments are conducted using 0.6m long, 12mm wide THEVA TPL4120 and TPL2100 2G HTS tapes. Closed HTS loop is formed using face-to-face soldered lap joints with an overlap length of 20 mm. The joints are manufactured using a purpose built soldering system with controlled dwell time, temperature, and applied pressure. Experimental testing identified the best performing parameters as 50 s, 423 K, and 83.3 kPa, respectively. The circulating current is measured using a calibrated Hall sensor coupled to an iron core current transducer. All preliminary flux pump experiments are conducted in a liquid-nitrogen bath at approximately 77 K. The HTS charging equation itself consists of an inductive voltage term coming from the inductance of the HTS loop $[L_{\mathrm{HTS}}]$ and a resistive voltage term because of the solder joint resistance $R_{\mathrm{j}}$ as in the equation (3): $$ L_{\mathrm{HTS}}\frac{\mathrm{d}I_{\mathrm{HTS}}}{\mathrm{d}t} + R_{\mathrm{j}}I_{\mathrm{HTS}} = \overline{V}_{\mathrm{FP}}. \tag{3} $$

The PMFP energize the HTS loop to a maximum current of approximately 129 A with a pumping rate of around 65A/s and has a steady-state peak to peak current oscillation of around 50A. Whereas, the reference TWFP reached approximately 100 A with a pumping rate of 17A/s at 15Hz input AC frequency. The steady state peak-peak ripple is also higher around 60A. Subsequent TWFP design and control studies shows the air gap, excitation frequency and current waveform as important performance parameters. Reducing the air gap to 0.5 mm increases the maximum HTS current by 16.7% relative to the 1mm air-gap design. Increasing the excitation frequency reduced the time required to charge the loop to the maximum possible current from around 15s at 5 Hz to around 5s at 15 Hz. Further experiments will investigate different supply parameters to optimize the TWFP performance.

The results demonstrate the feasibility of both flux pump configurations and identify electromagnetic geometry and excitation control as effective routes for improving TWFP performance. A temperature controlled cryogenic chamber has additionally been constructed and is being commissioned to extend the investigation over 60K - 90 K using full-scale 2G HTS double-pancake coils. This work provides an experimental basis for the future integration of stationary flux pumps with superconducting field windings for offshore wind-turbine generators.

Keywords: 2G high-temperature superconductors; Flux pump.

Speaker: Adithya Harithas Venkatesh (Helmut-Schmidt Universität, Universität der Bundeswehr, Hamburg)

12:00 Numerical Study of AC Loss Reduction in MW-Class Fully HTS Wind Turbine Generators for Reduced Cryogenic Requirements

AC loss in high-temperature superconducting (HTS) stator windings is a key constraint in fully HTS rotating electrical machines, as it directly determines the cryogenic cooling load and thermal management requirements. In practical operation, HTS stator windings are exposed simultaneously to rotating magnetic fields and AC transport currents. The resulting AC loss is therefore not simply the sum of magnetization and transport losses, due to their electromagnetic coupling. Under a given machine performance requirement, balancing these two loss components is essential for minimizing the total AC loss and associated cryogenic load. In this work, the AC loss characteristics of HTS stator windings are numerically investigated using a MW-class axial-flux fully HTS wind turbine generator as the reference machine. The effects of generator geometry, stator winding configuration, and HTS conductor type on AC loss are systematically evaluated. Finite-element models based on the T–A formulation are developed, incorporating interpolated Ic(B,θ) characteristics to account for the dependence of critical current on magnetic-field magnitude and orientation. A moving-mesh technique is employed to capture the transient electromagnetic behaviour associated with rotor motion. The results demonstrate that appropriate optimization of the machine geometry and stator winding parameters can effectively reduce the total AC loss. In particular, reducing the perpendicular component of the magnetic field, Bper, is identified as an effective approach for mitigating AC loss and cryogenic cooling requirements. These results highlight the importance of coordinated optimization of electromagnetic and winding parameters for reducing AC loss and enabling efficient cryogenic and system-level design of fully HTS generators.

Speaker: Shuangrong You (The University of Edinburgh)

12:15 FAST – Fast actuator using superconducting technology

Superconductivity has the potential to be an enabling technology for future high-tech systems. Coils wound from commercially available superconducting (REBCO) tape are uniquely suited to produce high magnetic fields at high current densities. This has applications in varying fields from motors and actuators to plasma containment in fusion, from MRI and NMR to high-voltage power transport.
In order to gain experience using ReBCO superconductors and cryogenics in high-tech industry we at VDL ETG are designing and building a demonstrator linear motor using superconductivity. The linear motor design consists of a conduction cooled DC stator array of superconducting racetrack coils and conventional copper AC coils in the mover. The three phase demonstrator actuator is designed to accelerate and decelerate the mover at 1000 m/s2, over a stroke of 100 mm. The superconducting coil array targets a peak magnetic field of 7T at 25K. A thin wall, flat cryostat is required to insulate the HTS coils, while allowing the mover to be in atmospheric conditions.
In this talk we will discuss the design effort of the 100g demonstrator. We will show the cooling and insulation method of the design and discuss the challenges we meet while designing and building the demonstrator.

Speaker: Mathijs van Gorcum (VDL ETG Technology & Development)

12:30 → 13:45 Lunch

13:45 → 15:00 Poster session

Poster Session with coffee and refreshments

13:45 A helium gas-cooled test bench for hyper- and superconducting aviation cables.

We present the design, assembly and commissioning of a modular test bench to investigate the electrical and thermal performance of aviation-relevant power cables and terminations under a wide range of steady-state or dynamic loading conditions.

Particular focus is placed on demountable custom cryogenic flanges and high current feedthroughs, providing a high degree of flexibility for the test bench.

A promising route towards sustainable aviation combines LH2, fuel cells, and compact electric motors linked by a low-weight cryogenic distribution network that may consist of high-purity aluminum (hyper-conducting) or of superconducting cables. To validate the design of such cables and auxiliary technology under operational conditions and to test their resilience to various failure scenarios, a dedicated forced-flow GHe test bench is built, allowing for tests at temperatures between 50 to 100 K; at He gas pressure levels up to 10 bar; and He flow rates up to 50 g/s.
The closed-loop GHe flow is driven by a cryofan and re-cooled with a single-stage cryocooler. Its pressure and temperature are measured at multiple locations and compared to model predictions of the cable-, heat exchangers- and joints behavior. Also cable current and voltage are monitored to evaluate its electrical stability and AC losses, while inductive antennas are used to analyze the current distribution within the cables.

Speaker: Margreet ter Schure (University of Twente)

13:45 A Modular Distributed Cryogenic Cooling Solution for Long-Distance HTS Power Cables

High-temperature superconducting (HTS) power cables are moving toward large-scale and long-distance applications, placing increasing demands on the efficiency, reliability, and maintainability of cryogenic systems. Conventional cooling architectures generally rely on centralized cryogenic stations and long-distance circulation of subcooled liquid nitrogen. As cable length increases, this approach leads to higher pumping requirements, larger temperature rises along the cable, and increasing system complexity.To address these limitations, this paper proposes a modular distributed cryogenic cooling solution for long-distance HTS power cables. The key idea is to replace long-distance transport of cooling capacity with distributed local refrigeration. Compact cryogenic units are installed along the cable to provide local recooling and circulation. Since practical HTS cable systems inevitably require cable joints, these locations can also be used to integrate standardized cryogenic modules, thereby reducing additional infrastructure requirements.Based on this concept, two system configurations are proposed. In the segmented-loop configuration, each 500 m–1 km cable section operates as an independent liquid-nitrogen circulation loop. In the relay configuration, the liquid-nitrogen flow path remains continuous, while intermediate cryogenic stations provide local recooling and pressure boosting. Compact Stirling-type hybrid pulse-tube cryocoolers and highly integrated reverse-Brayton cryocoolers are considered as candidate refrigeration platforms.By shifting from centralized long-distance cooling to distributed local refrigeration, the proposed solution decouples cryogenic performance from total transmission distance and enables a modular and scalable system architecture.

Speakers: Xiaotao Wang (Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (TIPC-CAS)), Mr Haibing Li (Lihan Cryogenics)

13:45 Current Transport Experiments on REBCO Coated Conductors in Liquid Neon Compared with Liquid Hydrogen Experiments

To expand the application range of high-temperature superconducting (HTS) conductors, the transport characteristics of REBCO coated conductors were evaluated under liquid hydrogen and liquid neon cooling conditions. Although REBCO conductors maintain their superconducting state at the liquid nitrogen temperature of 77 K, their intrinsic performance cannot always be fully exploited in applications involving high current densities and high magnetic fields. Cooling to the 20–30 K temperature range markedly enhances the critical current density, enabling current densities more than an order of magnitude higher than those at 77 K.
Liquid hydrogen is one of the candidate coolants for this temperature range; however, its flammability imposes substantial safety-management requirements. Liquid helium is nonflammable but suffers from high cost, limited availability, and operational constraints. In contrast, liquid neon has a boiling point of approximately 27.1 K and can provide a cryogenic environment comparable to that of liquid hydrogen. As a nonflammable noble gas, it is an attractive coolant for evaluating HTS applications in the 20–30 K temperature range.
A measurement system has been developed to evaluate the V–I characteristics and stability of REBCO coated conductors under liquid neon cooling at approximately 27 K. Prior to the experiments, the cooling
energy required to liquefy 200 cm^3 of neon was estimated from the enthalpy difference between neon gas at 300 K and saturated liquid neon at 27.1 K near atmospheric pressure. The required heat removal was calculated to be approximately 90.5 kJ. Assuming an effective cooling capacity of 5 W, the liquefaction time was estimated to be approximately 5.0 h, indicating that several hours are required for the liquefaction process in liquid neon experiments.
The measurement system is based on an inductive current-excitation method. A sinusoidal current is applied to the primary coil, inducing a transport current in the secondary superconducting loop through electromagnetic induction. The V–I characteristics of the conductor are then obtained from the secondary-side response. This technique enables transport-characteristic evaluation without introducing large currents directly into the superconducting conductor inside the cryostat. In this study, a Fujikura REBCO coated conductor incorporating a BHO-doped EuBCO superconducting layer was employed as the test sample.
The measurement system, liquefaction analysis, comparison between liquid hydrogen and liquid neon cooling experiments, and conductor stability are presented and discussed based on the experimental results.

Speaker: Rise Takagi (National Institute of Technology, Gifu College)

13:45 Development of a high-capacity, high-efficiency GM Cryocooler and supercritical helium circulating cooling system for HTS applications

HTS applications demand Gifford-McMahon (GM) cryocoolers with higher cooling capacity and efficiency at relatively higher temperatures. HyMaster has developed a high-efficiency single-stage GM cryocooler (HMR1020) achieving 104.4 W at 20 K, corresponding to a relative Carnot efficiency (rCOP) of 11.5%. Reliability testing is performing currently being performed to ensure long-term product performance.
Based on this large-capacity GM cryocooler, a 20 K supercritical-helium circulation system has been developed, providing rapid precooling and steady cryogenic operation for high-temperature superconducting (HTS) systems. The demo system equips four HMR1020 GM cryocoolers for cooling and a cryogenic turbine fan for helium circulation. This paper presents the system configuration, key design parameters, and preliminary performance testing results.

Speaker: Dr Yingzhe Wu (Shanghai HyMaster Technology, Co., Ltd.)

13:45 Experimental comparison of the heat transfer performance of conventional copper braids and neon pulsating heat pipes as thermal links between a cryocooler and an HTS coil

Cryocoolers are increasingly favored over bath or forced-flow cooling systems for providing heat removal and thermal stability in High Temperature Superconducting (HTS) magnets. Efficient heat transfer between coil and cryocooler is crucial to the operation of such a system. Compared to conventional thermal buses, which are typically made of solid materials such as high-purity copper braids, the Pulsating Heat Pipe (PHP) -a passive device that operates through thermally induced two-phase flow- offers superior heat transfer performance at a reduced mass. PHPs are commonly constructed from a capillary sized tube bent in serpentine between an evaporator (in contact with the coil) and a condenser (in contact with the cryocooler). This configuration minimizes the bulk while allowing large areas of the magnet to be cooled. The tube is filled with a cryogenic fluid at saturation conditions. Heat is efficiently transferred by a combination of latent and sensible heat transfer mechanisms. In addition to being efficient, lightweight, and passive, it functions as an autonomous thermal bus and switch, capable of operating in zero-gravity, high-magnetic-field and high-radiation environments. For these reasons, the Paul Scherrer Institute (PSI), in collaboration with the VDL Enabling Technologies Group (VDL ETG), has launched a project to design, manufacture, characterize, and apply cryogenic PHPs for enhancing the cooling efficiency and reliability of cryocooler-based HTS magnets. This project belongs to PSI’s SMILE (Superconducting Magnets to Improve the Efficiency of Large Research Facilities) program that seeks to develop efficient energy superconducting magnet technology that will increasingly replace resistive magnets currently in use in large research facilities of the Paul Scherrer Institute.
This work presents an experimental comparison between conventional copper braids and neon-filled PHPs used as thermal links between a cryocooler and an HTS coil. The objective is to compare magnet coil temperatures obtained with neon PHPs and copper braids having the same cross-section and adiabatic length, for transferring heat generated by AC losses in an insulated HTS coil. The coil was tested with currents varying from 0 to 500 A, using ramps of 500 A/s and a 0.1 s plateau. The dedicated test bench developed at PSI is first described, followed by the HTS coil, the PHPs, and the copper braids used in the experiments. Finally, the experimental results obtained with neon PHPs and copper braids are analyzed and compared, demonstrating proof of concept and quantifying the heat transfer improvement achieved with neon PHPs.

Speaker: Jacob Cornelis Maris (VDL ETG Technology & Development B.V.)

13:45 Experimental Study on Large Cooling Capacity GM-JT Cryocooler in Liquid Helium Temperature Range

The Joule-Thomson (JT) cryocooler precooled by Gifford-Mcmahon (GM) cryocooler features high cooling efficiency and large cooling capacity, with a compact configuration, no moving parts at the cold end, and the capability for long-distance cooling power transport, making it suitable for applications such as superconducting electric levitation, gas liquefaction, and pre-cooling of millikelvin-level cryocooler units. In this study, a large-capacity GM–JT cryocooler operating in the liquid helium temperature range is experimentally investigated. The configuration of the experimental system and the overall cryocooler architecture are described, followed by offline performance tests of the JT compressor to characterize its operating characteristics. The cooling performance of the integrated GM–JT cryocooler is evaluated under different operating conditions. The experimental results demonstrate that the cryocooler achieves a cooling capacity of 5.9 W at 4.2 K with a total input power of 9.0 kW, corresponding to a relative Carnot efficiency of 4.43%.

In this work, an experimental investigation of a large-capacity GM–JT cryocooler operating in the liquid helium temperature range is conducted. The study includes offline performance testing of the JT compressor and integrated low-temperature performance evaluation of the complete GM–JT cryocooler on a dedicated experimental platform. Cooling capacity, input power, and relative Carnot efficiency are systematically measured under steady-state operating conditions. The experimental results show that the cryocooler achieves a cooling capacity of 5.9 W at 4.2 K with a total input power of 9.0 kW, corresponding to a relative Carnot efficiency of 4.43%.

Speaker: Dr Yunhao Cui (Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (TIPC-CAS))

13:45 Inductive Current Distribution Sensing on HTS CORC Cables: Simulation, Design and Measurement

For models of HTS cables for large-current transfer applications, an accurate prediction of current distribution over the strands is important, as this forms the basis for many AC loss- and stability simulations. Especially in non-fully transposed multiple-strand cables, such as those of the CORC geometry, carrying a non-DC transport current, strand current distributions may be highly non-uniform. In this study, a current-distribution/AC-loss model of the electrical-network type is used to simulate current distributions, as well as the corresponding axial component of the cable’s magnetic flux time-derivative. Subsequently, this same axial flux-derivative signal is measured on a 0.6 m, 8-layer CORC sample using inductive pickup coils. The measurements and simulation show good correspondence, providing a validation tool for the current-distribution network model that is complementary to and independent from measuring the voltage over the cable. These results strengthen the use-case of these types of electrical-network models for calculating loss- and stability behavior of HTS current transmission cables of the CORC- or similar geometry.

Speaker: Jurrie Bruggeman (University of Twente)

13:45 Integrated DC Qualification of a Single High-Temperature Superconducting Cable Link for Cryogenic Electric Propulsion

Future electric aircraft require lightweight and high-power-density electrical transmission systems. High-temperature superconducting (HTS) cables are therefore promising for cryogenic electric propulsion, but their practical application requires coordinated evaluation of the cable, terminations, electromagnetic behaviour, and insulation. This work develops a modular single-cable cryogenic platform for the integrated DC qualification of an HTS cable link. Critical-current tests were performed to evaluate the DC transport capability, while segmented voltage measurements were used to characterize the resistance of the soldered cable-to-copper terminations. A two-dimensional electromagnetic model was established to analyse the self-field and current-density distributions under DC operating conditions. Insulation-resistance and withstand-voltage tests were also conducted to verify the electrical integrity of the cable assembly. The proposed platform enables the superconducting cable, electrical terminations, and insulation system to be assessed within the same cryogenic setup, providing a practical basis for component-level performance identification and the development of reliable HTS power links for cryogenic electric propulsion and future high-power electric aircraft.

Speaker: Prof. Wei Wang (Sichuan university)

13:45 Morphing a (nano) 0.002”D M5 (Mach 5) HSS (hypersonic stochastic switch) USP9550586B2 (choke) into an enumerated 0.001K superconductive electron/stripping QQTRON© (CHOKE) consisting essentially of a compounded/shafted aperture wherein Hψ = Eψ with ψ = Schrödinger wave function of the (quantum/ relativistic) Hamiltonian Ħ flux, a warp.

Because state of the art cryocoolers suffer from (CARNOT) inversion syndrome because of the 2nd law of thermodynamics wherein (heat/energy/charges) can only flow from higher to lower/charge levels, the HSS (hypersonic stochastic switch) an eigenvalue (condition of optimality in nature underscoring the power of Boltzmann “distributions” (i.e. extreme ((quantum/relativistic)) stochastic randomness) an 80K multiplier in Borel/galactic space (in the hypersonic domain), wherein the speed of light morphs ABS/ZERO ((dynamically)) given the infiniteness of the speed of light in Borel space. Instant presentation will hence focus on (1) the SPINNX© HSS (hypersonic stochastic switch) (VT May/2013) art (2) HICS (hypersonic (isentropic) cosines switch) electron stripping inversion art (VT Aug/2018) (3) SQS (supercritical quantum switch) art VT Sept/2018 (4) uniqueness of atm. air conforming as refrigerant (with O2 the enabling catalyst) (5) postulating GOL (gravity of light) as the dimensionless ((galactic)) quantum/relativistic tensor wherein Gg = GOL/g = 114M/g (indexed at g= 32.2ft/sec2 computationally) (6) postulating elemental blackholes hence as the 1st derivative of the entropy of the universe) analytically @2.77Boltz (speed of light expressed in natural log exponent) with 20 Boltz = 1,000BN x speed of light nominally = 1TRK/ABS in conformance with the enumerated speed of light synthesis underscoring 2nd law of thermodynamics (7) electron/stripping Gibbs (free/energy) the enabling QQTRON© eigenfunction/vector morphing ABS/ZERO (dynamically) (8) scalability and (9) dissecting the HSS (hypersonic stochastic switch) USP9550586B2 quantum/relativistic nexus (date/stamp January 2023) in support of the “EXTREME (ZERO.K) BLACKBULB COUPLE IN THE CRYOGENIC ZONE” topic underscoring the (July 2023) ASME/DC SHTC2023 presentation, predicated likewise on the “Cryogenic heat and mass transfer conference” (Twente) 4-5 November 2019, conversely (10) predicated on the “Cryogenic Kettle” synthesis .

POSTSCRIPT: See https://www.utwente.nl/en/tnw/ems/ecd-2020/Events/chmt/ University Twente 2019 generally and POSTER slideshow at https://www.utwente.nl/en/tnw/ems/ecd-2020/Events/chmt/p8-twente2-chmt2019-janeke-poster-slides-refined-7nov2019.pdf conversely. Also "A hypersonic stochastic switch is a patented mechanical and aerodynamic concept developed by inventor Charl E. Janeke (Constellation Dynamics LLC). It is designed to manipulate extreme airflow and thermodynamic states for aerospace and industrial applications.” (Google AI). Finally see “21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter.” June 2019 Abstract: Hypersonic Cryogenics: Stochastic Shock Compression Modelling. https://meetings.aps.org/Meeting/SHOCK19/Session/V1.54

Speaker: Charles Janeke (ASME)

13:45 Multidisciplinary design optimization of cryogenic mixed-refrigerant cycles

Cryogenic mixed-refrigerant cycles (CMRC) are a promising technology for the efficient cooling of HTS applications including power cables and current leads. Their efficiencies and lowest achievable temperatures are largely determined by the mixture composition and the heat exchanger design, both of which can be optimized using evolutionary algorithms.
Current modeling concepts involve first determining the optimum process parameters with an assumed heat exchanger performance, followed by optimizing the heat exchanger design. This approach, however, neglects the influence of actual heat exchanger characteristics, such as longitudinal heat conduction and non-constant pressure drop, on the optimum process parameters. In contrast, a multidisciplinary design optimization (MDO) optimizes process parameters and heat exchanger geometry simultaneously, exploiting the interdependency between disciplines to find the best solution.
In this contribution, the integration of a monolithic solver for heat exchangers into a process simulation framework is presented. Established MDO formulations and search strategies are discussed in the context of CMRC optimization and their suitability is evaluated.

Speaker: Mr Jakob Reichert (Karlsruhe Institute of Technology)

13:45 Three Approaches to 20 K Pulse Tube Cryocoolers for High-Temperature Superconducting Applications

Achieving hundred-watt-class cooling near 20 K is critical for the development of high-temperature superconducting (HTS) magnets, yet remains challenging for regenerative cryocoolers. This work presents recent advances at Tongji University in three pulse tube cryocooler (PTC) configurations designed to improve phase control, recover expansion power, and enhance cooling capacity.

The displacer type PTC uses a gas-driven displacer to control the phase relationship between pressure and mass flow while recovering part of the expansion PV power. Experiments on the connecting tube and on auxiliary inertance tube or orifice phase shifters showed that these components can improve phase matching and system performance. Two-stage displacer type PTC achieved minimum temperatures of 15.6-16.9 K in the reported configurations.

The shared inertance tube PTC connects the hot ends of two pulse tubes to a common inertance tube, enabling the redistribution of phase-shifting capability and PV power between the cold heads. An analytical model combining the dual Helmholtz resonator analogy with the transfer matrix method was developed to clarify the phase-shifting mechanism and guide system design.

The third configuration is a two-stage thermally coupled GM-type PTC using active buffers. The prototype reached a minimum temperature of 7.8 K and delivered a cooling capacity of 100.1 W at 19.99 K. It also provided 50 W at 14.13 K. These results demonstrate the feasibility of hundred-watt-class cooling near 20 K for HTS applications.

These results demonstrate the feasibility of hundred-watt-class cooling near 20 K and provide a promising cryogenic solution for HTS magnet applications.

Speaker: SHURUI ZHANG (Tongji University; Cardiff University)

13:45 TITLE: Morphing a (nano) 0.002”D M5 (Mach 5) HSS (hypersonic stochastic switch) USP9550586B2 (choke) into an enumerated 0.001K superconductive electron/stripping QQTRON© (CHOKE) consisting essentially of a compounded/shafted aperture wherein Hψ = Eψ with ψ = Schrödinger wave function of the (quantum/ relativistic) Hamiltonian Ħ flux, a warp.

ABSTRACT;
Because state of the art cryocoolers suffer from (CARNOT) inversion syndrome because of the 2nd law of thermodynamics wherein (heat/energy/charges) can only flow from higher to lower/charge levels, the HSS (hypersonic stochastic switch) an eigenvalue (condition of optimality in nature underscoring the power of Boltzmann “distributions” (i.e. extreme ((quantum/relativistic)) stochastic randomness) an 80K multiplier in Borel/galactic space (in the hypersonic domain), wherein the speed of light morphs ABS/ZERO ((dynamically)) given the infiniteness of the speed of light in Borel space. Instant presentation will hence focus on (1) the SPINNX© HSS (hypersonic stochastic switch) (VT May/2013) art (2) HICS (hypersonic (isentropic) cosines switch) electron stripping inversion art (VT Aug/2018) (3) SQS (supercritical quantum switch) art VT Sept/2018 (4) uniqueness of atm. air conforming as refrigerant (with O2 the enabling catalyst) (5) postulating GOL (gravity of light) as the dimensionless ((galactic)) quantum/relativistic tensor wherein Gg = GOL/g = 114M/g (indexed at g= 32.2ft/sec2 computationally) (6) postulating elemental blackholes hence as the 1st derivative of the entropy of the universe) analytically @2.77Boltz (speed of light expressed in natural log exponent) with 20 Boltz = 1,000BN x speed of light nominally = 1TRK/ABS in conformance with the enumerated speed of light synthesis underscoring 2nd law of thermodynamics (7) electron/stripping Gibbs (free/energy) the enabling QQTRON© eigenfunction/vector morphing ABS/ZERO (dynamically) (8) scalability and (9) dissecting the HSS (hypersonic stochastic switch) USP9550586B2 quantum/relativistic nexus (date/stamp January 2023) in support of the “EXTREME (ZERO.K) BLACKBULB COUPLE IN THE CRYOGENIC ZONE” topic underscoring the (July 2023) ASME/DC SHTC2023 presentation, predicated likewise on the “Cryogenic heat and mass transfer conference” (Twente) 4-5 November 2019, conversely (10) predicated on the “Cryogenic Kettle” synthesis .
POSTSCRIPT: See https://www.utwente.nl/en/tnw/ems/ecd-2020/Events/chmt/ University Twente 2019 generally and POSTER slideshow at https://www.utwente.nl/en/tnw/ems/ecd-2020/Events/chmt/p8-twente2-chmt2019-janeke-poster-slides-refined-7nov2019.pdf conversely. Also "A hypersonic stochastic switch is a patented mechanical and aerodynamic concept developed by inventor Charl E. Janeke (Constellation Dynamics LLC). It is designed to manipulate extreme airflow and thermodynamic states for aerospace and industrial applications.” (Google AI). Finally see “21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter.” June 2019 Abstract: Hypersonic Cryogenics: Stochastic Shock Compression Modelling. https://meetings.aps.org/Meeting/SHOCK19/Session/V1.54

Speaker: Charles Janeke (ASME)

15:00 → 17:15 Oral Session - Novel Cryogenic and HTS Technologies III

Session chair: TBD

Convener: Adil Shah (The University of Edinburgh)

15:00 High-efficiency hydrogen liquefaction by active magnetic refrigeration

At the National Institute for Materials Science (NIMS) in Japan, a project on high-efficiency hydrogen liquefaction by magnetic refrigeration is being carried out under the JST-Mirai Program. Liquid hydrogen is a key medium for storing and transporting hydrogen as an energy carrier, yet conventional gas-cycle liquefiers rely on compression work and reach only 20–30% of the Carnot limit. Magnetic refrigeration, which exploits the magnetocaloric effect, requires no compressor and thus offers substantially higher thermodynamic efficiency. In this presentation, we report the recent achievement of more than 60% of the Carnot limit in the active magnetic regenerator over a temperature range around the hydrogen liquefaction temperature, together with other progress in the project.

Speaker: Koji Kamiya (National Institute for Materials Science)

15:15 Numerical Analysis and Experimental Research of Cryogenic System for the High-Magnetic Field HTS Test Platform

In order to improve the stability and comprehensiveness of the performance test of HTS conductor, a cryogenic system based on a 360 W@4.2 K helium refrigerator has been designed to provide 4.5 K-50 K test environment. This study conducts process simulation of the system, establishes the objective function for control parameters, and designs the optimal operation modes under different test temperatures ranging from 4.5 K to 50 K, along with the control strategies for key parameters such as flow rate, pressure, and heater power. At the same time, the reliability of the cryogenic system was verified through experimental study. This work thus can provide theoretical guidance for selecting operation modes and setting parameters of the cryogenic system at various test temperatures, ultimately enhancing experimental efficiency.

Speaker: Jingxin Zheng (Hefei Institutes of Physical Science, Chinese Academy of Sciences)

15:30 Integral Formulation for Simulating Current Distribution and AC loss in ReBCO Tape Conductors in a Ferromagnetic Environment

With ReBCO tape conductors increasingly being applied in electrical machines, understanding their rich behaviour in terms of current distribution and AC loss under applied currents and – magnetic fields in environments that include ferromagnetic materials is crucial. Such behaviour is often simulated with commercial Finite Element Method (FEM) software using, among many other techniques, the H- and T-A formulations. As computationally efficient alternatives to such FEM formulations, integral methods such as the Partial Element Equivalent Circuit (PEEC) method and Brandt’s method have successfully been implemented for various cable- and coil lay-outs at the University of Twente.
In this work, we expand our 2D PEEC formulation to include also the effects of non-linear ferromagnetic materials in the vicinity of the superconductor. The ferromagnetic domain is resolved with the Magnetostatic Moment Method (MMM), which is then implicitly coupled with the PEEC formulation. In addition, the model is benchmarked against analytical solutions and the T-A formulation implemented in COMSOL Multiphysics, showing a good agreement for a wide range of cases.

Speaker: Ruben Keijzer (University of Twente)

15:45 Development of a Compact Two-Stage Stirling Cryocooler for Superconducting Applications

This paper presents the development and experimental investigation of a compact two-stage free-piston Stirling cryocooler for superconducting applications. The cryocooler adopts a coaxial configuration, in which the compressor piston and two-stage displacer are arranged along a single axis, providing a compact structure suitable for integration with superconducting systems. The original design also incorporates gas bearings and an external-coil magnetic circuit to improve reliability and compactness.

To improve the low-temperature performance, different regenerator materials, including stainless-steel spheres, holmium-copper material, and stainless-steel wire mesh, were experimentally compared. After optimization, the cryocooler achieved a minimum no-load temperature of 14 K. At an operating frequency of 50 Hz and an electrical input power of 220 W, a cooling capacity of 1 W was obtained at 20 K.

The results demonstrate the capability of the developed cryocooler to provide compact refrigeration in the 20 K temperature range. Owing to its single-axis architecture, the cryocooler also shows potential for future integration with rotating superconducting electrical machines, where it may be mounted on the rotor and rotate together with it. The feasibility and performance under rotating conditions remain to be experimentally investigated.

Speaker: Xiaotao Wang (Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (TIPC-CAS))

16:00 Multiscale Simulation Framework for Stirling Cryocoolers

Several software packages are currently available for simulating the operation of Stirling cryocoolers. However, fully three-dimensional CFD models are computationally expensive and time-consuming, making one-dimensional models the preferred approach for system-level simulations. These models typically rely on empirical correlations to describe component behavior, yet such correlations are often difficult to obtain experimentally and may originate from studies conducted decades ago. Furthermore, incorporating newly derived correlations into existing simulation tools can be challenging. To address these limitations, we are developing a one-dimensional simulation framework, providing greater accessibility than traditional implementations. The framework is based on the direct implementation of the governing differential equations, enabling straightforward modification and extension of the model. In parallel, advances in computational power now allow physical correlations to be derived from CFD simulations of representative small-scale volumes. These simulations will be combined with tomographic characterization techniques, such as CT scanning of regenerator structures, to capture realistic component geometries. The resulting multiscale modeling framework facilitates design optimization at both the system and component levels while reducing the need for extensive experimental characterization.

The one-dimensional system model is implemented in Python using the Pyoomph package. This package enables the direct definition of the governing differential equations, providing greater flexibility and control than most existing simulation software. Internally, the equations are translated into Oomph-lib C++ code, allowing efficient numerical solution of the resulting system. A library of predefined components is being developed to facilitate rapid model construction. Components such as regenerators, compression and expansion spaces, heat exchangers, and connecting tubing can be combined with appropriate boundary conditions to form a complete Stirling cryocooler model. Additional physical phenomena can be incorporated by defining the corresponding differential equations, enabling the model complexity to be adjusted as required. Furthermore, the framework employs a time-stepping approach, allowing the simulation of transient operating conditions, such as the initial cooldown process.

The implemented cryocooler simulation framework was validated against our previous work on a high-frequency Stirling cryocooler, for which reference simulation results were available. The reference model was developed using Regen3.2, which resolves the thermodynamic processes within the regenerator while assuming ideal isothermal expansion and compression spaces. The two models predict similar temperature and pressure profiles, with cooling powers differing by less than 14% in the present implementation. The remaining discrepancy is primarily attributed to differences in the implementation of material properties, which are currently being refined to improve model accuracy.

Speaker: Rick Spijkers

16:15 Performance of a ReBCO linear-actuator under dynamic operation

The performance of a superconducting linear-actuator demonstrator is evaluated under dynamic excitation. The voice-coil type of device consists of a ReBCO layer-wound stator and a permanent magnet mover. Its design and its static performance were presented earlier, showing a 100 000–fold higher efficiency than copper-based actuators [1]. Under dynamic excitation however, as relevant to various applications, significant AC losses are expected. Furthermore, the ferromagnetic elements in the assembly add to this ReBCO loss and also directly affect the dynamic response of the system. To model this behaviour, an equivalent non-linear electrical circuit is formulated, incorporating also mechanical work, inertia and losses. The model is tested against experiments where the demonstrator is operated in different modes in LN2. Various excitation cases are considered: blocked-mover, free-moving and delivering work; and are presented in terms of active and reactive power flows.

Reference: [1] W.M. Verbruggen, et al. “A compact & efficient linear actuator based on a layer-wound ReBCO solenoid”, submitted to Superconductor Science and Technology.

Speaker: Wouter Verbruggen (University of Twente)

18:00 → 20:00 Dinner

Thursday 29 October

09:00 → 09:10 Welcome

09:00 Annual Symposium Welcome & Opening

Speaker: Prof. Hans van Oort (University of Twente)

09:10 → 10:20 Symposium Cryogenics & Superconductivity

Annual Symposium on Applied Superconductivity and Cryogenics
Morning Session - Big Science (Accelerators & Fusion)
Afternoon Session - Clean Aviation, Medical Applications and Ultra-High Field

Convener: Prof. Hans van Oort (University of Twente)

09:10 R&D in Magnet Technology at CERN

Overview of R&D in Magnet Technology at CERN with a focus on the HFM Programme

Speaker: Gerard Willering (CERN)

09:30 Quench & Stability R&D

Speaker: Mr Jan van Steenlandt (University of Twente)

09:45 Future Nb3Sn Demand for Fusion

Speaker: Dr Matheus Wanior (Bruker)

10:05 Eurofusion Collaboration with Twente

Eurofusion Collaboration with Twente (TBC)

Speaker: Mr Giulio Anniballi (University of Twente)

10:20 → 10:50 Coffee Break

10:50 → 12:00 Symposium Cryogenics & Superconductivity Special Event

Details will be published shortly.

Convener: Prof. Hans van Oort (University of Twente)

12:00 → 13:30 Lunch

13:30 → 14:30 Symposium Cryogenics & Superconductivity Joint Session: Einstein Telescope Joint Session

Einstein telescope Joint Session with COMET Workshop

Convener: Michiel van Limbeek (University of Twente)

13:30 (Plenary) Short Introduction to the Einstein Telescope

Speaker: Gideon Koekoek (Maastricht University)

13:50 (Plenary) Deepdive Vacuum & Cryogenic Technology Einstein Telescope

Speaker TBC

Speaker: Michiel van Limbeek (University of Twente)

14:10 (Plenary) Keynote Speech from Industry (DEMCON)

Speaker: Romaine Kunst

14:30 → 16:00 Symposium Cryogenics & Superconductivity

Annual Symposium on Applied Superconductivity and Cryogenics
Morning Session - Big Science (Accelerators & Fusion)
Afternoon Session - Clean Aviation, Medical Applications and Ultra-High Field

Conveners: Prof. Hans van Oort (University of Twente), Marc Dhallé (University of Twente)

14:30 Ongoing developments in the 14T Dynamic Programme

14T UHF MRI developments at Donders

Speaker: Dr Martijn Cloos (Donders Institute RU)

14:50 Coffee break

15:10 Whole body MRI testing and installation

Tesla Talk

Speaker: Mr Mike Pearson (Tesla Engineering Ltd)

15:25 HTS High Field Magnet Program at HFML-FELIX

HFML-FELIX HTS programs (TBC)

Speaker: Mr Andries den Ouden (HFML-FELIX)

15:45 AC Losses in HTS Motor Coils for Aviation

Jurrie Placeholder

Speaker: Jurrie Bruggeman (University of Twente)

14:30 → 16:00 Vacuum & Cryogenics – Bridging Research and Industrial Applications

COMET Workshop

Conveners: Michiel van Limbeek (University of Twente), Noa Avital (Oost NL)

14:30 Coffee Break

14:45 Industry's role in ET

OostNL

Speaker: Ms Noa Avital (OostNL)

14:55 Interactive session

Breakout sessions:
one moderator from the project team in each group
(Draft for team: Noa, Matthias, Judith, Albert)

15:50 Summary and follow-up contact points

LIOF

Speaker: Albert van Dorssen (LIOF)

16:00 → 17:00 MESA+ ET and Syperconductivity+Cryogenics Lab visits

17:00 → 18:00 Drinks & Bites