CHATS-AS 2026

Mar 9, 2026, 2:00 PM → Mar 12, 2026, 1:30 PM Europe/Zurich

Saariselkä, Ivalo, Finland

Tiina Salmi (Tampere University of Technology, Finland)

CHATS AS 2026 will be held on March 9-12 2025, hosted by Tampere University (Finland)

Objectives and Topics

The traditional focus of the workshop will be maintained on the modelling and related experimental validation of HTS/LTS superconducting systems, from cables to magnets, and related cryogenics, aimed at supporting their design and operation for nuclear fusion, particle accelerator, power generation and transmission, and other applications.

All different kinds of modelling, including but not limited to thermal-hydraulic, electromagnetic, thermomechanical, multi-physics and multi-scale will fall within the scope of the workshop.
 

The registration is now open: Register here by February 8 2026.

We acknowledge with gratitude the contribution of our sponsors, ESAS, IEEE, Luvata, and Quanscient, whose support helped us provide accessible registration fees and a furthter reduced student fee.

 

CHATS2026-Saariselka_Practical_info.pdf

Mon, March 9

5:00 PM → 6:30 PM Registration and Welcome: Welcome reception

Tue, March 10

8:25 AM → 8:30 AM Opening

Speaker: Tiina-Mari Salmi

8:30 AM → 10:10 AM Modeling methods and tools: Thermalhydraulics & Quench I

8:30 AM Modelling the thermo-hydraulic response of ITER TF coils under representative fast-discharge scenarios in the Magnet Cold Test Facility

The 18 Nb₃Sn toroidal field (TF) coils of ITER, based on cable-in-conduit conductors (CICC) cooled by forced-flow supercritical helium, provide a peak field of 11.8 T at the plasma and store about 41 GJ of magnetic energy, making controlled fast discharge a key aspect of the magnet protection strategy (Ref [1]). To support commissioning and ensure reliable integration into the machine, selected TF coils and PF1 will undergo full-scale cold tests in the ITER Magnet Cold Test Facility (MCTF), where the main objectives are to validate electrical, thermal and mechanical performance of the coils – together with their protection and insulation systems - under operational vacuum and cryogenic conditions, at currents up to the nominal 68 kA for TF coil (Ref [2]).
In this context, numerical modelling is essential to complement the diagnostics and support the definition of robust and efficient test procedures. Previous analyses have addressed fast discharge and quench behaviour of ITER TF coils at system (Ref [3]) and conductor level (Ref [4]) during plasma operation. However, published studies specific to the MCTF configuration remain scarce, despite their relevance for anticipating key transients and guiding test campaigns.
This work presents a set of electro-thermo-hydraulic analyses performed with the CryoSoft suite code (Ref [5], Ref [6]) on a detailed model of the ITER TF coil in the MCTF configuration. Two fast-discharge scenarios are discussed: (i) 34 kA with a 60 s decay, a time-constant-relevant case selected to limit the inter-terminals voltages (200 V); and (ii) 68 kA with a 5 s decay, the nominal-current discharge, that is identified as the ITER voltage-relevant scenario (4.1 kV) and generates significant eddy-current losses in the TF radial plates (~32 MJ) and case (~40 MJ). For both cases, the analysis resolves the coupled thermo-hydraulic behaviour of TF winding pack and TF case, including the forced-flow cooling of the CICC, the TF case-cooling loop and their mutual heat transfer. This integrated approach provides the transient temperature distribution in the pancakes, together with the evolution of helium pressure, mass-flow rate and energy deposition in the conductor and TF casing, allowing the identification of phases where thermal margins are reduced and providing temperature, pressure and voltage signatures for comparison with facility measurements. Altogether, these insights consolidate the physical picture of fast-discharge transients in the MCTF configuration, providing a robust basis for the preparation and interpretation of the test facility tests.

Ref [1] Neil Mitchell et al 2021 Supercond. Sci. Technol. 34 103001
Ref [2] Barabaschi et al., Fusion Engineering and Design 215 (2025) 114990
Ref [3] Fink et al., Fusion Engineering and Design, 75–79 (2005) 135-138
Ref [4] L. Bottura, Journal of Computational Physics, 125 (1), 26–41, 1996
Ref [5] L. Bottura et al., Cryogenics, 40 (8–10), 617–626 (2000)
Ref [6] https://htess.com/cryosoft/

Speaker: Serafina Baschetti

8:55 AM Modeling Thermal Coupling Effects in the ITER TF Coil

This paper presents a thermal network model of an ITER Toroidal Field (TF) coil pancake aimed at accurately simulating thermal coupling between conductor turns. The model is implemented within the CryoSoft THEA code and represents the pancake as a network of equivalent thermal resistances and capacitances, enabling efficient and physically consistent prediction of heat transfer paths among adjacent turns. A key advantage of the proposed approach is the exploitation of THEA’s adaptive meshing capabilities, which allow localized refinement in regions of steep temperature gradients and provide enhanced resolution of quench initiation and propagation.
The paper details the model formulation, including the derivation of inter-turn thermal resistances and the numerical implementation in THEA. Simulation results are presented for both normal operating conditions and quench scenarios. The results quantify the effect of thermal coupling on peak temperature evolution, quench development, and propagation velocity. These findings highlight the importance of local mesh refinement for accurately capturing quench dynamics and thermal transients.

Speaker: Luca Bottura (CERN)

9:20 AM Quench analysis of the W7-X Non-Planar Coil operating at 1.8 T

The IPP team operated the W7-X superconducting magnet system at 1.8 T on the plasma axis in the last quarter of 2024. In contradiction to the standard 2.5 T operation the operating current in the conductors was significantly lower (11.027 kA vs. 15.32 kA). Both the lower magnetic field and the lower current affect the hotspot temperature in case of a fast discharge of the coils. Quench simulations were carried out using the THEA code by CryoSoft to study the quench behavior of the W7-X conductor operating at 1.8 T and estimate the maximum hot spot temperature for four different values of the time delay between the start of the heat pulse triggering quench and start of the current dump (0.5, 0.715, 2 and 3 s). The effect of the energy of the heat pulse initiating quench on the hot spot temperature and the Joule heat generation in the strands and in the jacket were analyzed. The development of voltage during a 10 second operation at 1.8 T and constant current was also studied. The observed differences between the quench evolution in the W7-X conductor operating at 1.8 T and at 2.5 T were analyzed and discussed.

Speaker: Prof. Monika Lewandowska (The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences)

9:45 AM Thermo-Hydraulic Analysis of the EUROfusion DEMO TF LAR Coil

In 2024, EUROfusion consortium released a new DEMO baseline with a slightly reduced aspect ratio (A=2.8 instead of 3.1), major radius (8.6 m instead of 9.1 m) and magnetic field (4.4 T instead of 5.2 T on the plasma axis) compared to the previous 2018 baseline. The fusion power is targeted to 1.65 GW. The design of all DEMO magnets have been updated in 2025. In this study, we present the thermo-hydraulic analysis of the TF coil based on the flat react&wind Nb3Sn conductor. The coil design aims at optimizing the material and manufacturing costs of the TF coils, and simplifying the manufacturing process. The thermo-hydraulic analysis investigates the possibilities of reducing the magnet’s operating costs and increasing the coil robustness against unforeseen degradation of its superconducting properties or higher-than expected heat load, both requiring increased cooling power.

Speaker: Dr Kamil Sedlak (EPFL-SPC)

10:10 AM → 10:25 AM Coffee break

10:25 AM → 12:05 PM Modeling methods and tools: Thermalhydraulics & Quench I

10:25 AM 4C code qualification: validation against data from the cooldown of the EAST TF magnets

Nearly two decades after achieving its first plasma in 2006, the Experimental Advanced Superconducting Tokamak (EAST) continues to serve as a key device for superconducting magnet technology, being the first tokamak to employ both toroidal and poloidal superconducting coil systems. Its Toroidal Field (TF) coil system consists of sixteen coils, each approximately 4 m in height, operated at cryogenic temperatures around 4.5 K through forced-flow cooling with supercritical helium (SHe) at about 3.8 bar. Reaching these operating conditions requires a prolonged thermal transient—the magnet cooldown—during which the coil temperature is progressively reduced from ambient to cryogenic temperature.
The Cryogenic Circuit, Conductor and Coil (4C) code, developed at Politecnico di Torino more than 15 years ago, is a dedicated thermal-hydraulic simulation tool for superconducting fusion magnets. It has undergone extensive verification and validation exercises across a wide range of relevant transients, from fast quench scenarios to slow cooldown processes, and is increasingly used to support the design and safety assessment of magnet systems for next-generation tokamaks.
The 4C code is here applied to model the cooldown of the EAST TF coils, representing the first validation of the tool against experimental data for a full-magnet cooldown in an operational tokamak. The simulation employs measured boundary conditions—namely the inlet temperature and the inlet/outlet pressures of the SHe flow—and predicts the evolution of the outlet temperature. These results are then quantitatively compared with experimental measurements to assess the predictive accuracy of the thermal-hydraulic model.
This validation effort represents a significant step towards the qualification of the 4C code for its use in future fusion devices, particularly in contexts where licensing processes increasingly require certified, validated thermal-hydraulic tools. Its successful benchmarking against EAST data will further strengthen its position as a reference tool for superconducting magnet thermal-hydraulic modeling. It will indeed be reliably applied also to the design and operation of the magnet system of the China Fusion Engineering Test Reactor (CFETR).

Acknowledgements
This work was supported by the Comprehensive Research Facility for Fusion Technology Program of China under Contract (No. 2018-000052-73-01- 001228).

Speaker: ROBERTO BONIFETTO

10:50 AM Modelling Quench in Magnets with Internal Dump

This work presents a numerical modeling framework for quench protection in the non-planar superconducting magnets of the GIGA stellarator reactor (Gauss Fusion), which store energies on the order of 100 GJ. The study focuses on the development and application of a predictive multi-physics model for an innovative active protection concept that eliminates external dump resistors by using the structural steel plates of the winding pack as distributed resistive elements for energy dissipation. The approach is based on an integrated simulation model coupling the THEA code, specialized in one-dimensional thermo-electro-hydraulic modeling of superconducting cables, with a dedicated electrical circuit model. The THEA component resolves the transient behaviour of the conductor in both LTS (Nb₃Sn) and HTS (REBCO) configurations, including quench initiation and front propagation, helium coolant dynamics, and current redistribution. The circuit model represents the current paths through the steel plates and evaluates their electro-thermal response. The model simulates quench initiation mechanisms through localized thermal disturbances and critical current degradation, as well as detection logic based on voltage and temperature thresholds. Following protection triggering, the coupled model captures the transient transfer of current from the superconductor to the resistive steel plates and the associated Joule dissipation of magnetic energy. A systematic parametric study is performed using the model to assess sensitivity to geometric, thermal, and electrical design parameters, interfacial insulation properties, conductor characteristics, and quench detection strategies. The simulation results demonstrate the capability of the model to predict autonomous protection performance, hot-spot temperature suppression, and low-voltage operation, providing quantitative guidance for the design of simplified cryogenic and power system architectures.

Speaker: Mr Matteo Lanzolla (CERN)

11:15 AM Numerical analysis techniques for evaluating electromagnetic and thermal characteristics of spiral copper-plated striated coated-conductor cables under ac operation conditions

Spiral coated-conductor cables feature a structure where HTS coated conductors are wound in layers around a metal core. Their high thermal stability, high current density, and high mechanical flexibility make them promising candidates for applications in magnets and electrical machines. In particular, spiral copper-plated striated coated-conductor cables (SCSC cables) are expected to be applied in ac environments due to their multifilament structure, which reduces ac losses and tape magnetization.
When considering cable design, numerical analysis techniques for evaluating electromagnetic and thermal characteristics, such as ac losses, quench, and thermal runaway, are important. Conventional analyses of spiral coated-conductor cables often employ cross-sectional models that do not account for the cable's intricate three-dimensional shape. However, the three-dimensional spiral winding configuration of coated conductors significantly influences their electromagnetic and thermal characteristics. On the other hand, numerical analysis that fully simulates the cable's three-dimensional geometry is impractical from a computational load perspective. Therefore, an appropriate modeling technique capable of considering the cable's three-dimensional geometry is required.
We have developed an electromagnetic field analysis model and a quench analysis model for SCSC cable considering cable’s three-dimensional geometry. The electromagnetic field analysis model is primarily used for calculating ac losses in SCSC cables. The model enables visualization of electromagnetic phenomena when SCSC cables carry alternating current under external ac magnetic fields—conditions that most closely resemble actual application environments. A key feature of this model is its ability to evaluate ac losses considering the current distribution among layers in the SCSC cable. This is achieved by combining the finite element method with a simplified circuit model. The quench analysis model calculates the longitudinal temperature distribution of the coated conductors and core constituting the SCSC cable, along with the heat exchange between them, using the heat conduction equation. It also represents the SCSC cable as a circuit model consisting of resistances and inductances to compute the current distribution. By iterating between temperature distribution calculations and current distribution calculations, it enables the evaluation of quench phenomena when an alternating current is applied to the SCSC cable.

This work was supported in part by JST-ALCA-Next Program Grant Number JPMJAN24G1, Japan, and supported in part by JSPS KAKENHI Grant Number JP22K14238.

Speaker: Dr Yusuke Sogabe

11:40 AM On the mode based regime apdatiation for quench propagation model in CICC

Bringing back the substantial idea of hybrid contact discontinuity (A. Shajii and J. P. Freidberg, 1996), thermally coupled 1-d fuild-solid system is carefully repriced on the fundamental question what is the best approach to the quench propagation model of superconducting CICC (cable-in-conduit conductor). By means of a mode analysis with the exact dispersion relation, the simple equations of temperature flow just reveals the regimes of flow speed to discern when the fluid is coupled enough under heat transfer with the conductive solid in parallel. Therefore, broken equilibriation from the unstable mode 2 is interpreted as the upper limit of hybrid contact by a dimesionless quantity of thermal Péclet number. In consequence, the analysis just explains the regimes of normal zone propagation as a possible rationale on THQB (thermal hydraulic quench back) too. Thus, a hybrid approach of numerical scheme emerges according to the discriminated regimes, i.e., of Joule-heat driven reaction-diffusion (Regime 0), equilibriated propagation in hybrid contact (Regime A) and decoupled hot front of advective flow (Regime B). To support the idea to design an effective numerical scheme, further investigation is carried out with numerical experiments not only to check the behavior of the predicted limit, but also to justify the non-conservative form in temperature with which the numerical solution is sound enough in terms of front tracking as well as conservation laws. As a result, we suggest a hybrid numerical model of quench propagation, and discuss our idea, comparing with the existing codes of implicit FEM in non-conservative form (Gandalf, Mitrandir and THEA) and the recent alternatives based on Riemann solvers of the conservative equations (S. Mao's discontinuous Galerkin code and REIMS).

Speaker: Dr Dong Keun Oh (Korea Institute of Fusion Energy)

12:05 PM → 2:00 PM Lunch

2:00 PM → 3:40 PM Modeling methods and tools: Electromagnetics I

2:00 PM Numerical modelling of HTS response to magnetic field in perpendicular geometry

The non-uniform magnetic field and current density distribution inside superconductors must be considered for properly assessing critical aspects in the design of high-field magnetic systems. Understanding the static and dynamic magnetic behavior of High Temperature Superconductors (HTS) has significantly progressed thanks to the development of space- and time-resolved experimental techniques. Among them, Magneto Optical Imaging (MOI) stands out as a non-destructive method capable of providing quantitative information on local magnetic flux distributions with micrometer-scale resolution [1].
In this work, we investigate the magnetic response of high-quality YBa2Cu3O7-x thin films deposited on single crystal substrates (MgO and YSZ). MOI measurements were performed at different temperatures, in perpendicular geometry, i.e., with the applied field directed perpendicularly to the HTS film. The MOI technique enables the direct reconstruction of the spatial distribution of supercurrent density and its dependence on the local magnetic flux density and temperature.
To complement and interpret experimental observations, we developed numerical simulations based on an H-φ formulation [2] on the FEM software COMSOL Multiphysics®. This approach accurately captures the electrodynamic behavior of the HTS film, including field penetration and current redistribution during applied field ramps. The agreement between simulated and measured magnetic field profiles validates the predictive capability of the numerical framework.
Overall, the combined experimental and numerical analysis demonstrates that the model provides a fast and reliable tool for investigating current limiting mechanisms, assessing sample inhomogeneities, and understanding the influence of microscopic defects, on the electromagnetic performance of HTS films. This achievement is of utmost importance for predicting the behavior of HTS tapes in high-field magnet designs.

Speaker: MARTINA CASCIELLO

2:25 PM Simulating Quench in Metal Insulated Racetracks using Finite Element Methods

Quench protection is difficult in HTS magnets due to slow quench propagation – the coils are often overheating before the associated resistive voltage can be detected. Coil winding technologies without electrical insulation between coil turns are being developed to cope with this problem. In these coils, the operation current can by-pass the quenched cable segment to neighboring turn and slower down the hotspot temperature development. In applications requiring ramping of magnet current and good field quality, such as accelerator magnets, turns insulated with metal strips have emerged as an option. The quench behavior and protectability of large metal insulated coils still remains to be analyzed. The existing quench models consider mostly solenoids, where one can profit from axisymmetric modeling assumptions. In this contribution, we explore 3D simulation of metal insulated racetrack geometries with FEM. This allows flexible generation of coil geometries and the ability to simulate local quenches. The challenge is the need for dense meshing and convergence issues due to thin layers which can have very different material properties. We use Quanscient Allsolve software to simulate small racetrack coils with H-phi formulation and run the simulations in cloud. We compare solutions and model performances when meshing both the HTS tape and metal layer, as well as when replacing the metal insulation with thin shell approximation. We report the quench propagation behavior in small racetrack coils, considering the impact of different metal insulation characteristics, and discuss about scaling the models to larger coils.

Speaker: Tiina-Mari Salmi

2:50 PM Electrical Behavior of GIGA Stellarator Magnet System with a Low-voltage Fast Discharge

Conventional fusion magnet system typically discharges the stored energy by external discharge resistors as a quench protection with a relatively short time constant, such as < 15 s for ITER magnets [1]. However, the resulting coil voltage to ground can exceed several kV, increasing the risk of accidental Paschen discharge or arcing. In addition, quench protection relying on the external resistor needs numerous vacuum penetrations through the cryostat. This is particularly critical for the stellarator magnet system requiring much more coils than those of Tokamak device.
To address these issues, GFG proposes a concept of an innovative low-voltage fast discharge where the discharge time constant is long as > 40 s. This drastically reduces the coil voltage as the targeted voltage is 500 V from terminal to ground. Additionally, internal magnet structure works as the dump resistor, which drastically reduces the number of feeder lines and the penetrations of vacuum barrier. These features would not only reduce the risk of electrical failures but also relax the requirements for the insulation system and complexity of the magnet system.
In this study, we have investigated the peak voltages appearing in 40 coils of the GIGA magnet system with an electrical network model built on LTSpice. The simulation results indicate the necessity of varistor unit for surge voltage mitigation, and demonstrate that the proposed method successfully limit the coil voltage to less than +/- 500 V.

[1] I. Song, A. Roshal, V. Tanchuk, J. Thomsen, F. Milani and I. Benfatto, "The fast discharge system of ITER superconducting magnets," 2011 International Conference on Electrical Machines and Systems, Beijing, 2011, pp. 1-6, doi: 10.1109/ICEMS.2011.6073779

Speaker: Shin Hasegawa (Gauss Fusion GmbH)

3:15 PM Modeling of electric faults in the ITER TF magnets

The ITER project represents a cornerstone of the global effort to achieve controlled thermonuclear fusion, with the objective of demonstrating the feasibility of sustaining a burning plasma and paving the way for future fusion power plants. Among its most critical subsystems are the Toroidal Field (TF) magnets, massive superconducting coils responsible for generating the strong and steady toroidal magnetic field necessary to confine the plasma. Owing to their large stored energy, intricate structure, and complex electrical environment, understanding their electromagnetic behavior, particularly under fault conditions, is essential to ensure safe and reliable operation.

This work presents a comprehensive analysis of fault scenarios in an ITER TF magnet. The TF coil model, implemented in Simulink, integrates the detailed electrical network of the TF magnet, the ground connections, and the Fast Discharge Unit (FDU), enabling the simulation of fault behavior during a fast discharge event. Several practically relevant fault cases were investigated, including magnet terminal–to–ground faults, double pancake joint–to–ground faults, double pancake joint–to–radial plate faults, and radial plate–to–ground faults. The primary objective was to identify the highest voltages arising during these events so that protection systems can be calibrated accordingly, preventing the possibility of subsequent cascading faults triggered by the initial failure.

A particular focus was placed on assessing the influence of distributed capacitances throughout the system. The analysis demonstrates that capacitive effects substantially shape the transient response, giving rise to overvoltage and oscillatory behavior during fault events. These resonance phenomena are shown to be linked not only to the model of the TF itself but also to the fast discharge unit (FDU) connected to it. The results highlight that a realistic model including all parasitic capacitances, both in the TF coil and in the FDU, is essential to evaluate the severity of fault-induced transients and to ensure that the insulation and protection design of the TF magnet system remains robust under all credible fault scenarios.

Speaker: Marco Breschi (Universita e INFN, Bologna (IT))

3:40 PM → 3:55 PM Coffee break

3:55 PM → 5:40 PM Modeling methods and tools: Electromagnetics I

3:55 PM Analytical and Numerical Analysis of Screening Currents in the HTS Muon Collider Cos-Theta Dipole

To achieve the realization of a 10 TeV Muon Collider facility and reduce the ring dimension to minimize muon decay, the main bending dipole magnets must generate high magnetic fields up to 16 T. Additionally, the superconducting coil aperture must accommodate thick tungsten shielding to protect the magnet from muon decay products. These challenging requirements motivate the investigation of high temperature superconductor (HTS) technology as a possible solution for the coil structure, exploring operating temperatures above liquid helium to potentially reduce the cost of cryogenics.
However, a large magnetization effect is induced by the persistent currents flowing along the wide HTS REBCO tapes to screen the external field. This phenomenon produces non-negligible effects, such as field quality degradation, hysteretic losses, and additional mechanical stresses on the conductor. Simulating these screening currents is essential but computationally expensive when performed numerically by Finite Element Method (FEM) software, significantly slowing down the iterative optimization process of magnet design.
For this reason, an analytical routine based on the Brandt model, capable of rapidly simulating the non-uniform current distribution, has been developed in MATLAB and validated by comparison with the numerical T-A formulation implemented in COMSOL Multiphysics.
The analytical model is proposed as a complementary tool to expedite the initial geometry optimization, rather than as a replacement for numerical solvers, which remain essential for performing detailed analyses.
This contribution presents the conceptual electromagnetic and mechanical design of the cos-theta dipole for the Muon Collider ring, where analytical and numerical methods have been employed synergistically to leverage the strengths of both design approaches.

Speaker: Francesco Mariani

4:20 PM AC loss estimation in round HTS cables

The Coated Conductor (CC) tapes appear to be promising for the production of magnets and cables due to their high critical magnetic field and temperature, as well as competitive critical current density, in combination with good mechanical properties. On the other hand, the superconducting layer may exhibit high energy dissipation in an external magnetic field due to the relatively large hysteresis AC losses resulting from the tape geometry. This could be a limiting factor of the ReBCO tapes application in a transient field specific to magnets. A significant impact on reducing AC losses is expected from tape filamentization, similar to the positive experience with using thin filaments in low-temperature superconducting wires. However, the ReBCO material must be covered with a metallic stabilizing layer to prevent the destructive effects of the atmosphere and to enhance the thermal and electrical stability of the wire, thereby reducing the effects of defects. The introduced coupling AC losses, caused by the transverse current between the superconducting filaments through the metallic stabilization, should then be carefully analyzed for future applications. The balance between the electrothermal stability of the conductor and the AC losses is achieved by selecting the correct parameters for the metallic stabilization layer. Here, we compare analytical and numerical (FEM) solutions for the AC losses estimation in round HTS cables, along with their verification through experiments.

Speaker: Dr Mykola Soloviov (Institute of Electrical Engineering, Slovak Academy of Sciences (SAS))

Wed, March 11

8:30 AM → 10:15 AM Modeling methods and tools: Thermalhydraulics & Quench II

8:30 AM Invited talk

9:00 AM Quench Protection in Insulated REBCO Conductors: Design Optimization and Fast Detection via REBCO SQD

Within the French exploratory program SupraFusion, we investigate fast and reliable quench detection and protection strategies for insulated REBCO coated-conductor stacks intended for fusion-relevant, high-field magnet systems. Because these insulated windings show very slow normal-zone propagation and hold large magnetic energies, conventional voltage-tap detection often reacts too late, letting the hotspot temperature reach damaging levels. Our aim is to develop strategies that improve detectability and make insulated REBCO stacks protectable without adding integration constraints.
We focus on two complementary techniques. The first relies on stabilizer-based protection, where the copper cross-section is adjusted to balance Joule heating with the slower voltage rise. The second makes use of a co-wound Superconducting Quench Detector (SQD): a slightly stabilized REBCO tape, thermally coupled but electrically insulated from the conductor, designed to generate a stronger voltage response for the same disturbance. The SQD’s behaviour is tuned by controlled deoxygenation through heat treatments, which reduce its critical properties (Tc and Ic) , allowing earlier detection while keeping the overall design simple.
To assess the reliability of these two approaches, we build one-dimensional electro-thermal models in THEA©. These simulations reproduce adiabatic quenches, examine the role of stabilizer content, and include an independent SQD circuit to capture its thermal and electrical evolution. The numerical results indicate that suitably thick stabilizer sections can keep the hotspot within acceptable limits, while the SQD—when given the right degradation level and operating current—detects the quench noticeably earlier than the main conductor, lowering the hotspot at detection. Overall, the modelling strongly supports the relevance of both protection techniques and provides clear guidance for the next test campaign.
Experimentally, calibration campaigns have confirmed that the deoxygenation process used to degrade the SQD tapes is both controllable and reproducible. The link between heat-treatment parameters and the reduction of Tc and Ic has been established, making it possible to fabricate SQDs with well-defined characteristics. In parallel, proof-of-concept experiments for both protection methods have already been carried out at liquid-nitrogen temperature on several stack-type conductors. These first results validate the enhanced sensitivity of degraded SQDs and show that conductors with optimized stabilizer content can be effectively protected. A new experimental campaign, covering variable temperatures and magnetic fields up to 3 T in the H0 facility at CEA-Saclay, is currently being prepared and is expected to be ready during the first semester of 2026.

Speaker: Hajar ZGOUR (CEA Paris Saclay)

9:25 AM Quench Modeling and Experiment on 10 kA HTS Insulated Coil

Fast and reliable quench detection is one of the key challenges in the development of HTS magnets with large stored energy, in the range of MJ and higher. Several temperature-based detection methods are under study at EPFL Swiss Plasma Center, including twisted-pair superconducting wires (SQD), shielded thermocouple chains (TCC) and fiber-optics sensing (FOS). Integrating them into the winding pack of a high-current insulated HTS double pancake coil, the quench dynamics is studied in this work both numerically and experimentally. Results of the COMSOL modelling as well as testing up to 10 kA at the initial temperature ranging from 10 K to 77 K will be presented.

Speaker: Nikolay Bykovskiy (EPFL SPC)

9:50 AM Quench analysis of HTS part of the hybrid Central Solenoid designed for the next generation experimental fusion device

The central solenoid (CS) of a tokamak is engineered to withstand significant fluctuations in operating currents and rapid changes in magnetic fields. These capabilities are essential for initiating plasma breakdown and ensuring subsequent plasma shaping and control. A novel design has recently been introduced for the CS system designated for the next-generation experimental fusion device. This new CS system consists of six stacked coils (CS3L, CS2L, CS1L, CS1U, CS2U, and CS3U) ), with each coil further divided into two submodules. The inner submodules, situated in the high magnetic field region, are made from YBCO high-temperature superconductors (HTS), while the outer submodules, located in the lower-field area, use Nb₃Sn. Among all the submodules, the HTS1U and HTS1L are expected to endure the most demanding conditions, experiencing the highest magnetic fields, as well as the greatest mechanical and thermal stresses. Each HTS module is constructed with five hex-pancakes, all wound with an identical conductor based on the HTS CORC (Conductor on Round Core) strands concept.
In the present study, we perform quench simulations in the selected HTS conductors using the THEA code by CryoSoft. The considered conductors follows the normal operation current scenario and quench is initiated by a heat pulse imposed at the moment and location where the global minimum temperature margin is reached. It is assumed that after the quench detection and a certain time delay the operating current is dumped exponentially and magnetic field profile along the conductor decreases proportionally to the operating current. The heat loads due to the magnetization, coupling and eddy current AC losses as well as heat transfer between the adjacent turns and layers of the considered conductor are taken into account. The analysis is aimed at estimation of the maximum hot spot temperature during quench.

Speaker: Aleksandra Dembkowska (West Pomeranian University of Technology in Szczecin)

10:15 AM → 10:30 AM Coffee break

10:30 AM → 12:10 PM Modeling methods and tools: Thermalhydraulics & Quench II

10:55 AM Electromagnetic and thermal modeling of a non-insulated multi-turn coil made by HTS tapes

Different magnetic confinement fusion projects, as SPARC, STEP, and EU DEMO among others, will (or are considering to) employ High Temperature Superconductors (HTS) in their magnet system, due to the possibility to generate an higher magnetic field if compared to Low Temperature Superconductors (LTS), which are considered the state of the art in superconductors.
Even if HTS would increase magnet performance, this technology presents a well-known issue on the quench, i.e., the Normal Zone (NZ) propagation is slower if compared to the LTS one, causing the present quench detection approaches to be less effective, since these are developed for LTS-based magnets.
The non-insulated (NI) configuration of HTS could be a way to further increase the current density of the coil and possibly to self-protect the HTS against quench, even though this behavior still needs to be fully addressed. Modeling NI coils is important to fully understand the complex behavior of the magnet and to predict its response.
In this work, a 3D model of a NI multi-turn coil made by HTS tapes is developed in STAR-CCM+. The model is used to simulate electromagnetic behavior of the coil with self-inductance and is validated against available experimental data; then the capability to address thermal phenomena is also added to the model, with the possibility to address in perspective other relevant physics, i.e. mechanics. This model represents a further step towards the reliable modeling of a non-insulated HTS magnet.

Speaker: Ms Silvia Pierri (NEMO Group, Dipartimento Energia, Politecnico di Torino, Torino 10129, Italy)

11:20 AM Developments of the D0 prototype HTS conductor: Advancing Quench Detection for High-Temperature Superconducting Magnets for SupraFusion

Suprafusion is a French exploratory program focusing on the development of high-temperature superconductors (HTS) to meet tomorrow's energy and societal challenges, using fusion needs as a vector for this research. In particular, the program aims to design, manufacture and test a large-scale HTS demonstrator magnet. To meet this goal, the program will follow a stepwise development plan with smaller mockups and prototypes to qualify the main demonstrator key technological bricks.
One important risk in the demonstrator development will be ensuring its safety against quench. Indeed, due to their slow normal zone propagation velocities, quench in HTS magnets are hard to detect and can totally damage a coil by the joule power deposited. To address this challenge, the first prototype (called D0) build in the framework of the SupraFusion program will aim to study the quench detection of HTS copper stabilized insulated coil.
The D0 prototype HTS conductor will be first wound as a one-layer spiral on a stainless steel mandrel with a bending radius of 60 mm. Then, the mandrel will be assembled with large copper pieces soldered to the conductor and ensuring a good electrical connection to the busbars. To ensure a homogeneous thermal map and allow parametric studies, the whole device will be actively cooled by forced flow supercritical helium. Finally, the D0 prototype coil will be inserted in a 9 T solenoid background field magnet called OPTIMIST. The design target is to operate this prototype and perform quench studies at 10 kA, 4.5 K under a field of nearly 10 T. Once under operation, this prototype will allow us to qualify several key aspects of our technology: the propagation quench velocity, the conductor hot spot temperature, the quench protection system sensitivity, the use of SQD HTS, the conductor critical current, etc.
Currently, the main design aspects of this D0 prototype are complete. It includes magnetic field and load line margin computations, thermoelectric studies on the electrical connections, cooling strategy and thermal map, mechanical behavior under load, and integration of the prototype in the MATTRCIS cold test facility. At the same time, the first preparatory samples for the final D0 sample were produced and tested with liquid nitrogen. These allowed us to control the winding of the conductor on its mandrel without degrading its critical current, to control the electrical contact resistance between the conductor and the copper mandrel, and to install a heater, potential taps, and HTS SQD.

Speaker: Clément Genot

11:45 AM Cost Exploration of the CS Cryo-Magnetic System for EU-DEMO

The DEMO (Demonstrator Power Plant) project is a magnetic-confinement demonstrator for a fusion power plant. Since the cryo-magnetic system is expected to represent a major cost, it must be carefully considered, particularly from the perspective of the superconducting material inventory and the associated cooling facility. In this paper, we explore the main cost factors of the cryo-magnetic Central Solenoid (CS) magnet system, inspired by the 2022 CEA design of the DEMO CS. We present a first attempt at optimizing a cryo-magnetic CS system by adjusting the operating temperature of the CS as a function of the superconducting material quantity, while maintaining a temperature margin of 1.5 K, defined with respect to the most demanding operating conditions and accounting for the variation of the current in the CS. The results show that reducing the amount of superconducting material can lead to a decrease in the overall cost of the whole cryo-magnetic system, despite an increase in the cost of the cryogenic system. The simulations are performed using Simcryogenics, combining 0D/1D representations of cryogenic components in the supercritical helium loop with 1D models of Cable-In-Conduit Conductors (CICCs) and associated piping.

Speaker: francois bonne (CEA IRIG DSBT)

12:10 PM → 2:00 PM Lunch

2:00 PM → 2:50 PM Modeling methods and tools: Electromagnetics II

2:00 PM REBCO Subscale magnet 2 (RS2): a field-angle optimized common coil design for a double-aperture accelerator magnets wound from tape-stack or Roebel cable

Following the CHART/PSI roadmap toward insulated REBCO-based high-field magnets, and after the completion of the first REBCO Subscale magnet (RS1), we aim to design a subscale demonstrator for a double-aperture high-field magnet featuring field alignment between the wide face of the cable and the magnetic field. The objective of this development is a reduction of field errors and ramp losses, wrt. To the standard common-coil configuration of RS1. This coil configuration would be compatible with tape-stack cable as well as Roebel cable. The latter cable would benefit from the large bending radius of the common coil as compared to a cosine theta and block coil [1], [2].
To avoid critical-current reduction due to mechanical strain, the coil configuration minimizes hard-way bending of the tapes. Although this work focuses on the electromagnetic design, several considerations informed by the RS1 experience at PSI are included to incorporate the stress-management concept into this coil configuration, which may be necessary for high-field dipoles. To assess the electromagnetic scalability of this concept toward high-field accelerator magnets, a preliminary 14 T configuration is also presented.
Finally, an energy-extraction–based protection study at 4.5 K and 20 K is presented to help determine the cable parameters, namely the number of tapes and the Cu/non-Cu fraction.
Acknowledgement: This work was performed under the auspices of and with support from the Swiss Accelerator Research and Technology (CHART). This work received financial support from and contributed to the HFM Programme, hosted at CERN.
[1] G. A. Kirby et al., “First Cold Powering Test of REBCO Roebel Wound Coil for the EuCARD2 Future Magnet Development Project,” IEEE Trans. Appl. Supercond., vol. 27, no. 4, pp. 1–7, Jun. 2017, doi: 10.1109/TASC.2017.2653204.
[2] M. Durante, C. Lorin, T. Lecrevisse, M. Segreti, G. Kirby, and J. Van Nugteren, “Manufacturing of the EuCARD2 Roebel-Based Cos-Theta Coils at CEA Saclay,” IEEE Trans. Appl. Supercond., vol. 30, no. 4, pp. 1–5, Jun. 2020, doi: 10.1109/TASC.2020.2978788.

Speaker: Douglas Martins Araujo (PSI)

2:25 PM Instantaneous Power-Loss Modelling in HTS Conductors for Fusion Applications

Fusion magnets experience sharp dB/dt excursions, especially during plasma breakdown and current ramp-up. Calculating the instantaneous power dissipation is therefore essential for quantifying, through thermal-hydraulic simulations, the local heat load that must be handled. Toward this purpose, we have developed a modelling framework, combining analytical formulations with finite-element tools, to quantify hysteresis losses in REBCO tapes and coupling/eddy-current losses in advanced cable concepts such as sector-assembled cables (SECAS), twisted-stacked-tape conductors (TSTC), and highly-flexible-REBCO-conductors (HFRC). The approach builds on established analytical foundations, such as Brandt/Halse/Bean-type models for magnetization loss and Laplace-based formulations for coupling losses, and captures the interplay between superconducting and metallic dissipation mechanisms through field- and geometry-dependent descriptions of magnetization, effective transverse resistivity and coupling time constants.
Applied to EU-DEMO operating scenarios, the models show that magnetization losses dominate at high fields, while coupling losses become relevant during fast transients where the relaxation time τ governs the shielding of rapid dB/dt variations. These results indicate two key design directions for HTS fusion cables: (i) striated REBCO tapes to mitigate hysteresis, and (ii) sectorized conductors with increased effective transverse resistivity to enhance τ and suppress inter-stack coupling currents. The study also shows that sound analytical models can efficiently complement FEM simulations, providing fast and physically transparent estimations for the design of next-generation HTS fusion magnets.

Speaker: Gianluca De Marzi (INFN e Laboratori Nazionali di Frascati (IT))

2:50 PM → 3:40 PM Modeling methods and tools: Mechanics

2:50 PM Thermo-hydraulic and 3D mechanical analysis of the stresses in the electrical insulation of the W7-X non-planar coil during quench

Temperature variations during quench are a known cause of thermal strains and associated thermal stresses due to variation of the coefficient of thermal expansion between materials comprising the superconducting cable. In the case of the W7-X CICC, NbTi superconducting cable is placed inside an aluminum jacket wrapped with glass-epoxy electrical insulation. The strength of this composite material is limited to ~55 MPa in shear. The potential risk of the mechanical failure of this insulation was the subject of this study.
The thermo-hydraulic and electric analysis was conducted using the Cryosoft THEA software, which simulated two double layers out of six double layers of the entire winding pack (WP) of the non-planar W7-X coil (NPC). The heat transfer between the adjacent turns and layers was included, along with the inductance matrix computed by a dedicated FEM model. The impact of the electrical conductance for the contact between strands and jacket on the temperature evolution and hot spot temperature was studied.
The mechanical analysis consisted of building a detailed mesh of the entire WP and combining it with the existing FEM model of the NPC coil via bonded interface. The geometry and meshing were built via bottom-up method, parametrically, within the Ansys Mechanical APDL environment. With the possibility of controlling the mesh both in-plane and along the centerline of the coil. A mapping algorithm was created to read the temperatures from THEA and apply to the 3D mechanical model.
The orthotrophy of the electrical insulation was included by defining coordinate systems aligned with material orientation. The model was solved for the initial deformations and stresses after cool-down to 4.1 K and for temperature field at various time moments between 0.15-25 s identified as the most severe cases from the thermal point of view. The resulting stresses were compared with the allowable stresses obtained based on experimental data. Mesh dependence study was performed for the mechanical model to assess the sensitivity of the results.

Speaker: Rafal Ortwein

3:15 PM A holistic approach to include tolerances in the design process of superconducting magnets: the example of the Spin Rotators Solenoids for the EIC.

The design of superconducting magnets demands a multi-phase, multi-scale and multi-physics approach which can be more or less challenging according to the complexity of the requirements. According to the different schools, the design effort is usually performed in three or four phases: we can identify them starting from the simplest to the most complex as feasibility design, conceptual design, preliminary design, detailed design, with feedback loops in each phase. If we focus on the design of the cryostat and of the cold mass, the simplest loop consists in six steps: at first the design efforts focus on the magnetic design (step 1), which determines the parameters for the conductor design (step 2). Once the conductor and the geometric shape of the magnet are defined, the quench protection and transient analysis follow (step 3). Finally, the mechanical design of the cold mass (step 4) and the mechanical (step 5) and cryogenics design (step 6) of the cryostat complete the loop, with possible variations of the order of the steps according to the challenges the design encounter.
Compromises between each step are needed to guarantee both the compatibility of the design respect to the requirements and its physical and engineering feasibility.
The main limits of this approach are that: a) it is time consuming; b) according to the feasibility of the manufacturing (i.e., fabrication tolerances, conductor performances, etc.), sometimes the preliminary or the detailed design need to be modified. CEA is currently working on optimizing the design process of superconducting magnets with a holistic approach: during the feasibility and conceptual design phases we largely explore the parametric space of the design using the six steep loop and we guide the design with artificial intelligence algorithms. The principle behind is not only to find multiple local minima where the requirements are satisfied, but also to look at the curvature of the parametric space around these minima: the milder the curvature, the larger the tolerances that can be considered without changing the nominal design.
In this paper, the CEA approach is presented with an application example on the Spin Rotators Solenoids for the Electron – Ion Collider (EIC), where the conceptual design has been achieved thanks to ALESIA, the in-house artificial intelligence tool developed to guide the design process of superconducting magnet.

Speaker: Valerio Calvelli (Université Paris-Saclay (FR))

3:40 PM → 3:55 PM Coffee break

3:55 PM → 5:10 PM Modeling methods and tools: Mechanics

3:55 PM Toward the Magnet Design of the Main Block-Coil Dipoles of the Muon Collider Ring

The design of superconducting magnet for a high-energy Muon Collider continues to push the limits of present magnet technology, requiring new ideas that go beyond those encountered in conventional LTS systems. In this context, we are exploring a block-coil dipole concept specifically tailored to the unconventional boundary conditions imposed by muon physics: intense radiation from muon decay, tight geometric constraints and the need for both large aperture and ultra-high field. The design targets 16 T in a 140 mm bore, featuring an innovative stacked REBCO cable orientation and an unconventional end-winding concept.
In this contribution, we present the current status of our conceptual design, developed through a finite-element model implemented in ANSYS APDL. We focus on electromagnetic analysis, aimed to optimize the geometric field quality while maintaining the required operating margin on the load line and accounting of the impact of persistent currents due to the magnetization effects. Furthermore, we discuss our mechanical modelling approach based on a stress-management concept designed to meet the new mechanical paradigms introduced by HTS cable technology. We then present the corresponding mechanical analysis results, including the stress distribution induced by cool-down and energization.

Speaker: Luca Alfonso (INFN Genova)

4:20 PM Magnet Design for the Muon Collider Storage Ring

A Muon Collider is one of the most promising options for the post-LHC era, offering leptonic precision without the limitations of synchrotron radiation that affect electron machines. Its feasibility, however, is strongly constrained by the short muon lifetime (2.2 μs), which demands extremely rapid production, acceleration, cooling, and collision—posing severe technological challenges.
Among these, magnet design is one of the most critical. The collider requires very high magnetic fields and large apertures to host the shielding needed against the intense radiation from muon decay, while also meeting sustainability and efficiency goals. High-temperature superconductors, especially ReBCO, are the only realistic materials for achieving such performance, though their technological maturity still requires significant R&D and improved modelling.
This contribution presents the status of the preliminary magnet design, focusing on mechanical and electromagnetic aspects, and how these are modeled. In the first stage of magnet design, an analytical study was carried out to estimate the maximum achievable performance of dipoles, quadrupoles, and combined-function magnets as a function of peak field or gradient and aperture. Key constraints—such as allowable stress, protection feasibility, operating margin, and cost—were included in a simplified form.
Based on these results, a preliminary design of the ARC dipole (16 T, 140 mm bore) is now under way, exploring two parallel layouts—cos-theta and block-coil—to assess their respective strengths and limitations.

Speaker: Barbara Caiffi (INFN e Universita Genova (IT))

6:00 PM → 9:00 PM Social dinner

Thu, March 12

8:30 AM → 8:55 AM Modeling methods and tools

8:30 AM Numerical modeling of rotating high-temperature superconductiors with the T-A formulation

The T-A formulation of Maxwell’s equations in the magneto-quasistatic approximation is a popular approach for simulating the electromagnetic behavior of high-temperature superconducting (HTS) wires, cables, and coils. The mathematical formulation of the model is based on the magnetic vector potential A (B=curl(A)) for calculating the magnetic field in the entire simulation domain and of the current vector potential T (J=curl(T)) for calculating the current density in the superconductors.
In this contribution, we discuss the application of the T-A formulation to the case of rotating coils in an external static magnetic field. This requires the T-part that describes the induced current density and the electric field in the moving conductors to be expressed in the rotating frame. The critical point is the formulation of the coupling relationship between electrical parameters on the boundary of the A- and T- parts in order to guarantee the correct energy flux continuity.
First, the model is validated by a comparison with an analytical solution available for the case of constant resistivity and then by a comparison with the results obtained with the H formulation for the equivalent case of a static coil in a rotating field. Then, the model is applied to cases of increased complexity, including the case of transport current and of coupling with an external electric circuit.

Speaker: Francesco Grilli

8:55 AM → 10:10 AM Experiments and Validation: Experiments

8:55 AM Electrical properties of filamented and non-filamented REBCO superconductors under mechanical loading

High-temperature Rare-Earth Barium Copper Oxide superconductor tapes are considered for devices with time-varying magnetic fields, which means they will be affected by cyclic mechanical loading and AC losses. A recent trend for lowering the AC loss of REBCO tapes is filamentization. The influence of filamentization on the mechanical strength of REBCO tapes is being actively investigated – both via measurements and numerical modelling. However, due to the variance in inherent tape properties and the multi-layer structure of the tapes, it is not trivial to predict how in-depth numerical modelling should be for future predictions for cable or magnet design. To answer this question, we performed measurements on several non-filamented commercial tapes and two filamented non-commercial tapes to observe the difference in the behaviour, when subjected to mechanical loading. Numerical modelling was used to evaluate the resulting strain after mechanical loading for the non-filamented tapes. From the first results, we observed similar mechanical robustness for both tape types, suggesting that numerical models could be simplified to save computing time. On the other hand, local defects seem to play an important role also for mechanical behaviour, and the impact of filamentization on long-length homogeneity of tapes should be explored.

Speaker: Tomas Kujovic (Institute of Electrical Engineering, Slovak Academy of Sciences)

9:20 AM Operation performance of the High Temperature Superconductor Current Leads for Wendelstein-7X and JT-60SA

High Temperature Superconductor Current Leads, HTS-CL are essential components in superconducting fusion machines like ITER, W7-X and JT-60SA. They connect the electrical bus bars from the power supply system with the superconducting feeders of the different coil systems. KIT has designed, manufactured, tested and delivered 16 HTS-CL for W7-X and 26 HTS-CL for JT-60SA. Here, the operation experience of the HTS-CL in W7-X and JT-60SA is presented. Special attention is given to critical parameters, in particular to the contact resistances between the HTS section and the cold end and the copper heat exchanger (HX), the required He mass flow rate to maintain the temperature at the HTS-HX interface, the heat loss at the cold end, and the temperature margin in the HTS section. Finally, the quench protection of the HTS-CL is discussed.

Disclaimer: The work presented here expressed the views and opinions of the presenter and does not reflect those of the Karlsruhe Institute of Technology.

Speaker: Reinhard Heller

9:45 AM Experiments on HTS coils in the test facility at CERN: discussion on methods to validate models.

A large range of HTS cable and magnet design for high field accelerators is currently being studied and modelled, while the validation of models by experimental results is still rather limited. At the SM18 magnet test facility at CERN various types of HTS magnets have been tested, including insulated, metal insulated and non-insulated coils, with a range of instrumentation including high precision voltage measurements, fast voltage measurements for quench detection, acoustic measurements, pickup coils, temperature probes, etc. In the framework of HFM we are developing validation methods for splice measurements, V-I measurements, current distribution measurements, AC-loss, splice investigation, field mapping. We also define and experiment with various types of powering cycles to provide input for model validation.
In this contribution we will describe the various experimental methods, and we would like to share our experience with them so far.

Speakers: Franco Julio Mangiarotti (CERN), Gerard Willering (CERN)

10:10 AM → 10:25 AM Coffee break

10:25 AM → 11:15 AM Experiments and Validation: Experiments

10:25 AM Test results and analysis of REBCO Subscale magnet 1 (RS1) in various cryogenic environments

The decreasing cost and expanding production of REBCO tapes make them promising candidates for accelerator magnets operating at high current density and high magnetic field. Within the CHART program supporting accelerator-magnet development, we perform electromagnetic and thermal analyses of the first REBCO subscale (RS1) magnet developed in the MagDev Lab at PSI, designed to enable direct experimental comparison between HTS and LTS technologies. The RS1 magnet adopts the same configuration as a previously tested LTS SMCC common-coil magnet, in which the Nb₃Sn cable is replaced by a straight, soldered REBCO tape-stack cable with comparable geometric parameters. The magnet comprises four racetrack winding layers, with two layers located on each side of the aperture.
We present models of resistive and AC-loss induced heating in the REBCO stack under operating conditions relevant to superconducting magnets: liquid helium (4.5 K), gaseous helium (20 K), and liquid nitrogen (77 K). Magnetic-field harmonics and transient behavior in the REBCO cables are computed using an H–A formulation in FEM. The analysis further includes predictions for REBCO magnet protection using a dump resistor as well as alternative protection strategies. Numerical results are compared with experimental data from the two-layer configuration and the full magnet tested in liquid nitrogen, and predictions are provided for liquid- and gaseous-helium tests upcoming at CERN in 2026. These results support the development of accelerator magnets at higher magnetic fields where REBCO conductors offer significant potential.

Speakers: Dmitry Sotnikov, Douglas Martins Araujo

10:50 AM Methodology to predict the Tcs in ITER TF Coils based on Sultan Samples and TF Insert Coil Database

During operation, the Cable in Conduit Conductors (CICC) of the ITER Toroidal Field (TF) coils are exposed to severe electromagnetic forces [1]. These forces are in part hoop load and in part crushing load on the strands pressed by the Lorentz-force against the inner wall of the jacket. In addition, the differential thermal contraction between the steel jacket and the superconducting strands during the cooldown generates an additional contribution.

Given this complex stress-strain mechanics, the prediction of the current sharing temperature (Tcs) is not straightforward. However, its calculation during tokamak operation is important to assess accurately the temperature margin.

The concept of effective strain was developed in the past to analyse the performance of the ITER TF samples tested in the SULTAN facility, Villigen, Switzerland [2]. The effective strain was also applied to study the TF Insert (TFI), a single layer solenoid tested in the bore of the CSMC in Naka, Japan [3].

In this work, a methodology based on the cooldown strain and on the crushing strain is assessed from Tcs-measurements performed on straight samples tested in SULTAN during the TFIO campaign under different Lorentz-force conditions [4]. This campaign made it possible to build a large database on the performance of conductors from different manufacturers under different Lorentz-force levels. This allows one to derive the cooldown strain and the dependence of the crushing strain on the Lorentz-force for each type of conductor.

This methodology is then applied to the TF Insert (TFI). The Tcs in the TFI is predicted using the cooldown and crushing strain retrieved from the TFIO tests, and adding the hoop strain computed with FEM models. The predicted Tcs values are then compared with the measured ones. This comparison is important because it confirms that the parameters obtained from tests on straight samples, without the hoop strain contribution, can be applied to a coil.

The same methodology applied to the TF Insert is then applied to predict the Tcs in the TF coils during the tokamak operation. The Tcs maps computed in the TF coils are presented and discussed.

References
[1] C. Sborchia, Y. Fu, R. Gallix, C. Jong, J. Knaster and N. Mitchell, "Design and Specifications of the ITER TF Coils," IEEE Trans. App. Supercond., vol. 18, no. 2, pp. 463-466, 2008,
[2] M. Breschi, D. Bessette, and A.Devred, “Evaluation of effective strain and n-value of ITER TF conductor samples,” IEEE Trans. Appl. Supercond., vol. 21, no. 3, pp. 1969–1973, 2011.
[3] H. Ozeki et al., "Manufacture and Quality Control of Insert Coil With Real ITER TF Conductor," IEEE Trans. App. Supercond., vol. 26, no. 4, pp. 1-4, 2016.
[4] M. Breschi. L Cavallucci, V Tronza, N Mitchell, P Bruzzone and K Sedlak, “Impact of mechanical and thermal cycles at different operating conditions on the ITER toroidal field coil conductor performance,” Supercond. Sci. Technol., vol. 34, Art. no. 085021, 2021.

Speaker: Lorenzo Cavallucci (University of Bologna)

11:15 AM → 12:30 PM Discussion and Conclusions

12:30 PM → 1:30 PM Lunch