Abstract Fast and reliable quench detection remains a major challenge in the development of high-temperature superconducting (HTS) magnets with large stored energies in the megajoule range and above. Several temperature-based detection methods are investigated at EPFL Swiss Plasma Center, including twisted-pair superconducting wires (SQD), shielded thermocouple chains (TCC) and fiber-optics sensing (FOS). All three methods require strong thermal coupling to the main winding while remaining electrically insulated, thereby eliminating the need for high-voltage penetrations typically associated with voltage taps in fusion magnets. Their integration into the winding pack and their performance during quench events are studied on multiple samples of increasing size and stored energy, made of laminated stacked-tape soldered (LASSO) ReBCO conductors. These include a single racetrack coil tested in SULTAN using a 20 m-long 12-tape LASSO conductor and a double pancake coil tested in JORDI using a 50 m-long 15-tape LASSO conductor. Potential applications of the LASSO conductor and its industrial availability are also discussed.

The aim of this paper is to present a fast method capable of computing thermo-hydraulic transients in solid components that are cooled (or heated) by incompressible forced flow with or without external heating sources. By coupling the heat conduction equation in the solid volume to the heat transfer to the forced flow we derive a linearized mapping between the vector of input (control) quantities u(t) such as mass flow and inlet temperature to the vector of nodal temperature T(t) in the solid domain. A comparison between the newly developed code, which is finite volume based and a standard finite element-based code such as ANSYS is presented. Despite the significant reduction in CPU time, the finite-volume code well approximates the solid temperature field computed by ANSYS for the two cases considered here, i.e. the fusion power operation and vacuum vessel baking operation.

While the ITER assembly is progressing, a Magnet Cold Test Bench (MCTB) is also under preparation to test some of the ITER superconducting coils at 4 K up to nominal current before their installation in the pit. In this context transient Electro-Magnetic (EM) calculations were performed to estimate the impact of AC losses and eddy currents on the cryogenic and mechanical performance of the coils and other components of the MCTB. In particular the case of a fast exponential discharge is investigated, which represents the most severe transient operation expected for MCTB. Although different types of ITER coils are considered for the tests (several Toroidal Field Coils and Poloidal Field Coil number 1), the following discussion will be limited to the operation of a single Toroidal Field (TF) coil. Detailed results of the EM analysis, such as field maps, AC losses and QD voltages will be presented.

The 2023 ITER rebaselining includes the replacement of beryllium (Be) First Wall (FW) with tungsten (W). Furthermore, at the March 2023 Technical Coordination Meeting (TCM) the investigation of borated water in Vacuum Vessel (VV) - Primary Heat Transfer Systems (VV-PHTS) has been requested. In this context, scoping studies were made by using ITER C-Model, to assess the impact of these design changes on nuclear heating of different Plant Breakdown Systems (PBS). The pre-and post-processing of the calculations has been carried out using F4Enix, a new open-source Python package for Monte Carlo simulations input and output files parsing developed at Fusion for Energy (F4E). This paper wants to show and provide physical explanation of the results of the scoping studies, with particular attention to radiation shielding of superconducting magnets. The analysis evidenced that a thickness of at least 3 mm of W is needed to reach the shielding performance of 10 mm of Be, and that borated water provides relevant nuclear heating reduction mainly in the Toroidal Field Coils (TFCs), but its usability is limited by different technical reasons.

Muons offer a unique opportunity to build a compact high-energy electroweak collider at the 10 TeV scale. A Muon Collider enables direct access to the underlying simplicity of the Standard Model and unparalleled reach beyond it. It will be a paradigm-shifting tool for particle physics representing the first collider to combine the high-energy reach of a proton collider and the high precision of an electron-positron collider, yielding a physics potential significantly greater than the sum of its individual parts. A high-energy muon collider is the natural next step in the exploration of fundamental physics after the HL-LHC and a natural complement to a future low-energy Higgs factory. Such a facility would significantly broaden the scope of particle colliders, engaging the many frontiers of the high energy community. The last European Strategy for Particle Physics Update and later the Particle Physics Project Prioritisation Panel in the US requested a study of the muon collider, which is being carried on by the International Muon Collider Collaboration. In this comprehensive document we present the physics case, the state of the work on accelerator design and technology, and propose an R&D project that can make the muon collider a reality.

The development of analysis tools to calculate the activation of flowing water under irradiation is essential for fusion technology and for the ITER project. The Radio-Species Transport Model (RSTM) method is a simulation methodology developed by Fusion for Energy based on the Ansys Fluent (R) user-defined scalar (UDS) approach. It predicts the activation of a flowing fluid in domains where neutron fields and flow regimes require the coupling of activation and fluid dynamic effects. RSTM was successfully applied to ITER First Wall (FW) studies and benchmarked against experiments at the Frascati Neutron Generator (FNG). This research focuses on the application of the RSTM to the KATANA closed water activation loop at the JSI TRIGA Mark II fission reactor, as part of the EUROfusion Preparation of ITER Operation (PrIO) programme. Future work will compare these results with experimental data and other predictive tools including ActiFlow, GammaFlow (by UKAEA) and FLUNED (by UNED). In the next phase of operation, the KATANA facility aims to tackle experiments more relevant to ITER conditions. For this reason, Fusion for Energy is applying RSTM to design an alternative irradiation head that resembles the cooling circuit of an ITER First Wall panel, this being one of the main components where the water undergoes activation. This study shows the results of the RSTM tool for the current configuration of the JSI KATANA water activation loop. Conclusions are drawn on the relevance of the alternative ITER-relevant irradiation head for the next phase of the JSI water activation loop.

The aim of this paper is to review the possibilities to introduce potential functions for solving electromagnetic problems described by Maxwell’s equations. The focus of the discussion is on low frequency fields that can be treated by the magnetic quasi-static approximation. We target to present the possibility of solving the boundary value problems governing the potential functions numerically by the method of finite elements. In addition to results published by the authors in the last about forty years, some new formulations concerning the magneto-hydrodynamic equilibrium in plasma occurring in fusion devices are also presented.

This document is comprised of a collection of consolidated parameters for the key parts of the muon collider. These consolidated parameters follow on from the October 2024 Preliminary Parameters Report. Attention has been given to a high-level consistent set of baseline parameters throughout all systems of the complex, following a 10 TeV center-of-mass design. Additional details of the designs contributing to this baseline design are featured in the appendix. Likewise, explorative variations from this baseline set can be found in the appendix. The data is collected from a collaborative spreadsheet and transferred to overleaf.

As the International Muon Collider Collaboration advances the conceptual design for a multi-TeV muon collider facility, new technical constraints continue to arise in the muon production stage, where a high-power proton beam interacts with a target. Achieving the required muon bunch intensity may necessitate increasing the primary beam power up to 4 MW. Consequently, the shielding design must address sustained radiation exposure, particularly on critical components such as superconducting solenoids, which generate strong magnetic fields essential for capturing both pions and decay muons. Additionally, the portion of the proton beam that passes through the target without undergoing inelastic interaction leads to a very high power density in the chicane area and an intense ionising dose on the insulation material of the normal-conducting chicane magnets, which are used to separate the muon component. A robust method to safely extract these spent protons is crucial. This study presents the latest results from FLUKA Monte Carlo simulations, modelling the radiation load on solenoids and the extraction channel across varying beam power and target designs.

The "target and capture channel" is one of the crucial systems in a Muon Collider, whose function is to create an intense muon beam from the decay of the pions generated by a multi-MW proton beam impinging on a particle-producing target. To guarantee the capture of the pions and resulting muons, the channel consists of a sequence of solenoids, providing a well-defined profile on axis, with 20 T peak at the target location and an adiabatic decrease along the channel length. The solenoids of the channel need substantial shielding from the radiation heat load and dose originating from the nuclear interactions at the target, which results in large bore in excess of 1 m. In this paper we describe a concept for the target and capture solenoid, built with modules whose geometry is optimized to produce the required field profile while minimizing the stored magnetic energy of the system. All solenoids are wound with an internally cooled HTS cable. We focus here on the magnetic and mechanical design of the magnets.

Accurate prediction of the activation of fluids flowing under irradiation is important for the timely development of fusion technology. One of the major current issues is the cooling water of ITER, which becomes activated by plasma neutrons during nuclear operations, thus raising a number of radiological implications such as radiation effects on sensitive equipment, compliance with radiological protection zoning, and compliance with radioactivity limits in regulations of pressure equipment and effluents. Further significant applications are the activation of other service fluids in ITER and of the LiPb in both ITER and DEMO breeding blanket modules.To avoid systematic uncertainties, simulation of the activation of fluids flowing in arbitrarily complex 3D geometry, flow regimes and neutron fields requires full coupling of activation with fluid-dynamics physics models. No such tools were available until recently: the Radio-Species Transport Model (RSTM), based on the well-established ANSYS Fluent® UDS methodology, is one conceived and developed at F4E. Here we review the methodology and capabilities of the RSTM, as well as earlier development, validation, benchmarking and application activities. We then report currently ongoing further applications and benchmarking being performed in collaboration with specific tasks of the EUROFusion programme Preparation for ITER Operation. Computations, results and comparison with other methodologies for several cases of interest are presented and discussed.

This paper provides an overview on the engineering analyses workflow typically executed in support of the assembly and operation of superconducting magnet systems, in particular for ITER. Accurate field computations are required to evaluate (1) Lorentz forces as primary loads on magnets (2) cable temperature margins (3) critical error field harmonics and (4) field lines tracing. Although the required accuracy increases with each of these magnetic computations, their common aim, beyond use during machine design, is to provide estimates on the final alignment of magnetic fields and, possibly, to guide and adjust magnet installation. Two global mechanical models (18 TF and 2 TF coils) featuring their interfaces to the Pre-Compression Rings, CS and PF coils are used to assess the impact of tolerances and misalignments on the final coils' positions in operation so to guide, with the aid of metrology data, the assembly process. With these, we also evaluate the mechanical stresses during current tests at 4 K if performed before final installation. A global and several local models of the Pre-Compression Rings that must be mounted in the tokamak were developed and used to design the tightening sequence during PCRs assembly and the required assembly tooling. Magnet systems also require sophisticated models to predict conductor temperature margins and to assist during thermal transients (magnets cooldown). Thermal loads due to Joule losses in cold structures are evaluated with 3D eddy-current codes and nuclear heating with detailed Monte-Carlo models suited to simulate streaming and deep penetration 3D phenomena leading to nuclear power deposition in the cables.

The upgrade to JT-60SA tokamak (R = 3m, a = 1.2m) was conducted within a Europe-Japan collaboration agreement featuring the implementation of superconducting magnets. In 2021, the magnet system commissioning was initiated, undergoing cool-down and energization of the 18 Nb-Ti Toroidal Field (TF) coils (400 tonnes) up to full nominal current. TF energization was smoothly processed but it was observed during current load a higher outlet temperature increase of TF02 coil versus others, indicating a higher resistance in this coil circuit and therefore a possible risk in future operation. The present paper analyses the different risk factors that can impact the TF operation safety margins and their quantitative contribution. To this end on the one hand ad-hoc thermal & thermo-hydraulic models were developed by CEA and F4E to represent the TF02 whole circuit including feeder zone where high resistance is suspected to be located. The outcomes of those models on chosen TF and PF current scenarios including transient loads and their impact on temperature margin in risky zones such as terminal joint (TJ) are presented. On the another hand a 3D electrical circuit of TJ was modelled using TF cables tomography, giving a realistic quantitative insight into local current distribution, therefore on current sharing temperature. The analyses outcomes synthesis is depicted under strategic considerations and tentatively contributes to establishing guidelines for future operation scenarios in which magnets will undergo demanding conditions.

This document is comprised of a collection of updated preliminary parameters for the key parts of the muon collider. The updated preliminary parameters follow on from the October 2023 Tentative Parameters Report. Particular attention has been given to regions of the facility that are believed to hold greater technical uncertainty in their design and that have a strong impact on the cost and power consumption of the facility. The data is collected from a collaborative spreadsheet and transferred to overleaf.

The ITER magnet system comprises 18 superconducting Toroidal Field Coils (TFC) based on Nb 3 Sn conductor supplied with the operational nominal current of 68 kA to produce a toroidal magnetic field of 5.2 T at the plasma major radius R = 6.2 m. A Magnet Cold Test Bench (MCTB) to test the TFC at 4 K up to a current value of 68 kA is under construction at ITER Organization (IO) site. The foreseen test conditions are substantially different from those corresponding to the 18-coil operation as the coils will be tested individually in horizontal position and supported at a few locations along the case. On the one hand, the magnetic field distribution produced by one single coil yields a different pattern of Lorentz forces. On the other hand, the absence of case wedging results in a reduced structural stiffness of the analyzed system. Finite element analysis work on this subject has been reported in the past for the TF Winding Pack (WP) after impregnation without undergoing the enclosure in the case, showing that the TF WP could be tested in safe conditions at a reduced energization of 15 kA (20% of the nominal current). This work considers currents up to the nominal 68 kA and the TF case which provides additional stiffness to the coil. Prior to the energization load, the coil is subject to gravity and cooled down to 4 K.

A methodology to evaluate the neutron activation, categorize as radwaste, generate radiological checklists, and optimize the packaging for disposal of activated components according to French regulations is presented. The methodology obtains results like specific activity, dose rates and radwaste relevant parameters in a fine 3D mesh superimposed over the geometry of interest and can handle the typically complex models common in the nuclear fusion analyses like those of the ITER project. State-of-the-art radiation transport and activation codes are used along with a purposefully developed Python tool (F4E-radwaste), which performs the post-processing of the large amount of data generated and includes a graphical user interface. The 3D nature of the results allows the organization of packages of activated materials in a way that minimizes the amount of mass classified with higher radwaste levels and is subject to more stringent regulations and expensive disposals. An application case study of the methodology is presented for the In-Vessel Viewing System (IVVS) ITER system. The IVVS is especially suited as an example for this type of analysis as its elongated shape pointing towards the plasma results in a significant gradient of neutron flux and activation levels, and therefore radwaste categories. It is demonstrated how the methodology enables the reduction of the total higher radwaste level mass by optimizing the packaging of the IVVS radwaste.

The ITER blanket system safeguards the Tokamak's Vacuum Vessel and ex-vessel components from thermal and nuclear loads induced by the plasma. It comprises two parts: the First Wall panel facing the plasma and the Shield Block that provides the bulk of the shielding. The First Wall panels consist of Beryllium tiles on a CuCrZr layer, supported by stainless-steel structures which are cooled using a pressurized water circuit at 40 bar with an inlet temperature of 70 °C.Fusion for Energy has updated the thermal and mechanical analyses of ITER First Wall Panel 11 in preparation for the serial manufacturing. The panel will face heat flux up to 2 MW/m2 from plasma radiation, in addition to the volumetric nuclear heating, and the electromagnetic loads. A model with an enhanced detailed 3D geometry and heterogeneous materials indicates a 25% reduction of the deposited heating compared to the previous 2D model, from 625.4 kW (2D) to 455.4 kW (3D).The study embraces numerous thermal and mechanical analyses using Ansys software v19.2, incorporating 2D and 3D nuclear heating data. Responses are then compared and thus the possible impact of the two distributions on the thermal and mechanical behavior of the Fist Wall Panel 11 is assessed.

The Pre-Compression Ring (PCR) is an important component of ITER Magnet System. It is designed to generate a radial inward force on every Toroidal Field (TF) coil, putting in compression the shear keys, contrasting the bending of the inner leg and improving the stress distribution on the wedge surface. Stretching the PCR by tensioning 16 bolts on 4 counter flanges generates a total force of 47.8 MN on each coil. The application of such high preload, together with the large number of bolts to be tighten, the limited space available, and obviously the need of preserving the structural integrity of all the components, make this phase of the tokamak assembly far to be trivial. For these reasons, an in-depth analysis of the tightening procedure has been performed by means of FEM analysis, investigating the possible patterns and multi-step sequences to achieve the desired preload. The study led to a deep comprehension of the behavior of the system and permitted to identify and control the main critical aspects, i.e., the increase of stress in the PCR due to the ‘ripple’ and the variation of preload in some portion of the rings when the preload is applied in a different area, both due to the need of operating on a limited number of bolts at each time. The outcome of the investigation is the detailed definition of two multi-step tightening procedures suitable to be adopted for the assembly.

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.