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Superconductors play a crucial role in the advancement of high-field electromagnets. Unfortunately, their performance can be compromised by thermomagnetic instabilities, wherein the interplay of rapid magnetic and slow heat diffusion can result in catastrophic flux jumps, eventually leading to irreversible damage. This issue has long plagued high- J c Nb 3 Sn wires at the core of high-field magnets. In this study, we introduce a large-scale GPU-optimized algorithm aimed at tackling the complex intertwined effects of electromagnetism, heating, and strain acting concomitantly during the quenching process of superconducting coils. We validate our model by conducting comparisons with magnetization measurements obtained from short multifilamentary Nb 3 Sn wires and further experimental tests conducted on solenoid coils while subject to ramping transport currents. Furthermore, leveraging our developed numerical algorithm, we unveil the dynamic propagation mechanisms underlying thermomagnetic instabilities (including flux jumps and quenches) within the coils. Remarkably, our findings reveal that the velocity field of flux jumps and quenches within the coil is correlated with the cumulated Joule heating over a time interval rather than solely being dependent on instantaneous Joule heating power or maximum temperature. These insights have the potential to optimize the design of next-generation superconducting magnets, thereby directly influencing a wide array of technologically relevant and multidisciplinary applications. Flux jumps can lead to premature quenching and irreversible damage of superconducting magnets. Here, authors developed a GPU-optimized algorithm aimed at tackling the complex intertwined effects of electromagnetism, heating, and strain acting concomitantly on real superconducting coils.

The authors of our journal repeatedly expressed concern about the large number of accidents (electrical breakdowns) occurring at electrical, diagnostic, and cryogenic inputs into forcibly cooled superconducting magnets of fusion installations. However, the need for efficient measures for improving the reliability of the electrical insulation of these inputs, at least until last year, was ignored. In 2021, during the launch tests of Japanese-European tokamak JT-60SA, another accident occurred with an electrical breakdown at the electrical and diagnostic input into the tokamak, which, according to the project managers, would delay the launch of the tokamak by about 15 months.

Superconducting magnets are an invaluable tool for scientific discovery, energy research, and medical diagnosis. To date, virtually all superconducting magnets have been made from two Nb-based low-temperature superconductors (Nb-Ti with a superconducting transition temperature Tc of 9.2 K and Nb3Sn with a Tc of 18.3 K). The 8.33 T Nb-Ti accelerator dipole magnets of the large hadron collider (LHC) at CERN enabled the discovery of the Higgs Boson and the ongoing search for physics beyond the standard model of high energy physics. The 12 T class Nb3Sn magnets are key to the International Thermonuclear Experimental Reactor (ITER) Tokamak and to the high-luminosity upgrade of the LHC that aims to increase the luminosity by a factor of 5–10. In this paper, we discuss opportunities with a high-temperature superconducting material Bi-2212 with a Tc of 80–92 K for building more powerful magnets for high energy circular colliders. The development of a superconducting accelerator magnet could not succeed without a parallel development of a high performance conductor. We will review triumphs of developing Bi-2212 round wires into a magnet grade conductor and technologies that enable them. Then, we will discuss the challenges associated with constructing a high-field accelerator magnet using Bi-2212 wires, especially those dipoles of 15–20 T class with a significant value for future physics colliders, potential technology paths forward, and progress made so far with subscale magnet development based on racetrack coils and a canted-cosine-theta magnet design that uniquely addresses the mechanical weaknesses of Bi-2212 cables. Additionally, a roadmap being implemented by the US Magnet Development Program for demonstrating high-field Bi-2212 accelerator dipole technologies is presented.

In recent years, global investment in magnetic resonance imaging (MRI) has surged, with 3 T MRI technology overtaking 1.5 T as the standard in hospitals gradually. A combination of linear programming, genetic algorithms, and nonlinear programming was employed to design an actively shielded 3 T superconducting MRI magnet system. This magnet consists of seven main coils and two shielding coils, achieving a magnetic field with a peak-to-peak inhomogeneity of 10 ppm within a 50-cm-diameter spherical volume (DSV). To address the risk of quench in superconducting magnets, which can lead to damage due to excessive temperature, voltage, and stress, a quench protection system is crucial. The designed system segments the coils for protection, using diode pairs and shunt resistors to manage the quench. Initial simulations indicated that temperature rises and voltages were within safe limits, but some coils were slow to quench or did not quench at all, risking burnout. To mitigate this, quench propagation heating plates were added to increase the quench speed. Updated simulations showed rapid quench across all coils and a significant reduction in hot spot temperatures and peak voltages.

A topology optimization method based on sensitivity analysis is proposed for designing superconducting systems operating under critical current densities. The topology changes in the structure of the superconducting materials are achieved by creating air holes in the superconducting material and superconducting dots in the vacant space. The positions of the air holes and superconducting dots are determined via hole and dot sensitivity analyses. The hole and dot sensitivity expressions are derived based on the continuum sensitivity of the superconducting system. The proposed design optimization method can not only achieve fast convergence based on the sensitivity-based approach, but also alter the topology through the introduction of holes and dots and obtain a high-quality optimal solution. The level set method is used to express the topology and shape changes of the superconductors. The topology changes due to the air holes and superconducting dots are represented by adding a zero-level set to the newly formed material interface. The proposed method is validated through numerical examples involving the design of superconducting magnets. The results demonstrate that the hole and dot sensitivity analysis accurately predicts the optimal locations for air holes and superconducting dots to improve the system performance. Additionally, the design examples show that the holes and dots created near material boundaries accelerate shape optimization while minimizing the risk of the divergence.

High fracture toughness at cryogenic temperature and radiation hardness can be conflicting requirements for the resins for the impregnation of superconducting magnet coils. The fracture toughness of different epoxy-resin systems at room temperature (RT) and at 77 K was measured, and their toughness was compared with that determined for a polyurethane, polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Among the epoxy resins tested in this study, the MY750 system has the highest 77 K fracture toughness of KIC = 4.6 MPa√m, which is comparable to the KIC of PMMA, which also exhibits linear elastic behaviour and unstable crack propagation. The polyurethane system tested has a much higher 77 K toughness than the epoxy resins, approaching the toughness of PC, which is known as one of the toughest polymer materials. CTD101K is the least performing in terms of fracture toughness. Despite this, it is used for the impregnation of large Nb3Sn coils for its good processing capabilities and relatively high radiation resistance. In this study, the fracture toughness of CTD101K was improved by adding the polyglycol flexibiliser Araldite DY040 as a fourth component. The different epoxy-resin systems were exposed to proton and gamma doses up to 38 MGy, and it was found that adding the DY040 flexibiliser to the CTD101K system did not significantly change the irradiation-induced ageing behaviour. The viscosity evolution of the uncured resin mix is not significantly changed when adding the DY040 flexibiliser, and at the processing temperature of 60 °C, the viscosity remains below 200 cP for more than 24 h. Therefore, the new resin referred to as POLAB Mix is now used for the impregnation of superconducting magnet coils.

High dielectric strength, low thermal resistance and mechanical robustness are conflicting requirements on the insulation system between the superconductors in magnet coils and the quench heaters placed on the coil for active protection in case of a quench. To investigate possibilities to further improve the performance of quench heaters for future superconducting magnets, we have characterised polyimide, PEEK and fibre reinforced PEEK films that can be used to produce large flexibly quench heater circuits. The dielectric strength (at RT and at 77K), low temperature thermal conductivity, tensile strength (at RT and at 77K) and the force needed to puncture the different materials are compared.

The mechanical properties of Nb3Sn coils are strongly influenced by the adhesion between the impregnation resin and the coil constituents, which may impact the magnets’ performance. To improve the understanding of the parameters governing the adhesion in such superconducting magnets, a study was conducted on several impregnation systems with respect to different coil parts, notably copper, stainless steel, aluminium, and glass fibre. The study evaluated the adhesive strength in various test configurations, considering the influence of substrate surface conditions. The effect of cryogenic environment on the adhesion strength of the most commonly used epoxy resin was also studied. Additionally, the surface tension of the resins was measured, and an adhesion analysis was performed. The experimental adhesion results were found to be in accordance with the theoretical predictions of the adhesion analysis. The obtained results provide insights into potential modifications of the epoxy resin formulation and surface treatment methods to achieve specific wetting properties on the surfaces. This, in turn will impact the adhesion between the impregnation system and the coil constituents thereby potentially impacting the magnet’s performance.

Screening current is recognized as one of the critical elements limiting the progression of superconducting magnets toward achieving higher magnetic fields. Currently, most non-insulated (NI) superconducting magnets consider the magnet as insulated when addressing the issue of screening current. However, the bypass current in the NI magnet can modify the actual history of magnetization, so the screening current in NI magnet will be different from that in the insulated magnet. This paper presents a novel method based on the homogenized T-A formulation ( T is the current vector potential, and A is the magnetic vector potential), which enables real-time simulation of both the bypass current behavior and the implications of screening current in NI superconducting magnets, even when these magnets contain tens of thousands of turns. We have developed a 32 T NI hybrid superconducting magnet and validated the effectiveness of this method through experiments. Employing this efficacious method, we conducted a comprehensive calculation of screening current in NI magnets, comparing them with insulated magnets in terms of screening current-induced stress (SCIS), screening current-induced field (SCIF), and losses. The results indicate that in the NI insert coils, the sequential excitation of background coils and insert coils induces a reverse screening current, resulting in slightly lower SCIF and SCIS compared to those in the insulated magnets. The method and results can contribute to the enhancement of magnet design and provide valuable insights for the development of ultra-high fields (UHF) NI magnets.

We have designed a 30-T superconducting magnet for important experimental facilities in condensed matter physics research. The critical current of rare-earth barium copper oxide (REBCO) tapes directly or indirectly affects the electromagnetic margin, central magnetic field, hysteresis losses, field homogeneity, and screening current–induced stresses (SCIS) of the magnet. Given the poor critical current consistency of REBCO tapes at 4.2 K and their complex field-dependence, the arrangement of double-pancake (DP) coils is crucial in superconducting magnets. Based on measurements of over 100 REBCO tapes at 4.2 K and under an 8-T perpendicular field, we studied the arrangement of DP coils with different critical currents to assess their impact on the electromagnetic margin, central magnetic field, hysteresis losses, field homogeneity, and SCIS of the 30-T superconducting magnet. The results indicate that, depending on the magnet’s requirements for different performance aspects, DP coils wound with higher critical currents should be positioned in locations with lower sensitivity to critical current. This approach serves to reduce the operating factor, screening current–induced field (SCIF), peak hoop SCIS, and losses, respectively. These findings provide valuable insights into the design of ultra-high-field REBCO superconducting magnets and arrangement of DP coils.