The Superconducting Conductor Experimental Test Facility (Super-X) is a core component of the Comprehensive Research Facility for Fusion Technology (CRAFT), designed to conduct full-scale performance evaluations of superconducting conductors required for fusion reactors. Successfully cooling the background field superconducting magnet to its target temperature is the critical first step in the experimental process. However, in actual engineering tests, the limited number of temperature measurement points cannot fully capture the global temperature distribution of the magnet, making it even more challenging to accurately predict its evolution over time. To achieve real-time monitoring and prediction of the magnet’s temperature distribution and to effectively prevent cooling anomalies, this study proposes a novel deep learning model named ThermoNet. This model not only reconstructs the complete temperature distribution of the superconducting magnet from sparse temperature point data in real time but also predicts its evolution over a future time horizon. The model integrates the thermodynamic equations of the superconducting magnet, incorporates residual structures, and embeds a Convolutional Block Attention Module (CBAM) regulated by key physical scalars. This design not only significantly improves prediction accuracy but also enhances the model’s generalization capability and interpretability through deep physical guidance. In the Super-X cooldown simulation tests, ThermoNet achieved an average prediction error of 0.24 K with an inference time of 0.34 s. When validated in the experimental cooldown of the Central Solenoid Model Coil (CSMC), ThermoNet continued to perform reliably. Its temperature prediction error complied with engineering requirements, while maintaining an efficient average processing time of 0.30 s.

With the increasing demand for high-energy particles in accelerators, there is a need to develop compact, small-volume, and high-energy electron cyclotron resonance ion sources (ECRISs). As a key component in heavy ion accelerators and therapy facilities, ECRISs are capable of producing highly charged ions. A novel S-shaped hexapole magnet structure was proposed in 2016, which simplifies the distribution of Lorentz interaction forces in ECRIS superconducting magnets and facilitates achieving the required axial field. However, the fabrication of S-shaped hexapole poses significant challenges. Based on this design, we developed a superconducting S-shaped hexapole prototype for a 14.5 GHz microwave frequency using NbTi. A former with slotted ends was designed to enable the S-shaped winding. A small prototype of S-shaped hexapole used only one cable to realize winding, achieving a continuous uninterrupted winding both from the inside to the outside and from the outside to the inside. During 4.2 K cold testing, the coil attained a self-field of 1.5 T at a current of 480 A. Under an 8 T background field, it carried 232 A with only a single quench, reaching 98.22% of its load line.

To address the severe radial-edge artifacts and the loss of feature details in CT image reconstruction, this paper proposes a novel WF-Mamba algorithm integrating the Adaptive Wavelet Frequency Interaction Network (AW-net) with the Restructured Mamba Adjustment Module (RMAM). The AW-net leverages frequency-domain properties to initially enhance high-frequency components corresponding to edges and fine details in CT images. By integrating the Transformer architecture with the learnable 2D discrete wavelet transform (2D-DWT), we design the Optimized Encoding Block (OEB) and Wavelet Decoding Block (WDB) to improve the representation of image details and textures. Additionally, the Wavelet Aggregation Unit (WAU) is proposed to further enhance reconstruction quality by facilitating effective multi-scale information interaction. The RMAM incorporates a six-directional scanning mechanism to refine the initial reconstruction results generated by the AW-net, thereby enhancing the capture capability of fine-grained information and reducing computational complexity. To optimize model performance, a hybrid objective loss function is established by combining the L2 loss with Self-Supervised Wavelet Loss (SSWL). Experimental results demonstrate that the WF-Mamba achieves superior performance in eliminating radial edge artifacts, restoring textural details, and preserving boundary features compared with other discussed methods. Quantitatively, the WF-Mamba achieves a PSNR of 31.85 dB, an SSIM of 0.948, and a normalized MSE of 6.53 × 10-4 on the actual projection dataset, outperforming all compared methods. Furthermore, the reconstructed marked contour curves more closely approximate the reference image, demonstrating highly accurate restoration of the raw detailed structure.

Ba1-xKxFe2As2 (Ba-122) is a promising material for high-field applications due to its high upper critical magnetic field, low anisotropy, and minimal performance degradation under high fields. Recent advancements in both short and long Ba-122 tapes have brought practical applications within reach. Traditionally, high-pressure sintering via hot isostatic pressing (HIP) or hot pressing is utilized to densify the superconducting core and enhance critical current (Ic) performance. However, two major challenges hinder large-scale implementation: the high cost and technical complexity of large-scale HIP equipment, and the fact that Ba-122 becomes stress-sensitive after heat treatment, making the react-and-wind method impractical. To address these issues, we propose a two-step heat treatment method. In this process, the long tape is first coiled and subjected to a low-temperature pre-HIP stage in a compact HIP unit. Once the conductor or coil is formed, a subsequent atmospheric-pressure (AP) high-temperature sintering is performed. Experimental results show that this two-step process increases Ic by 33.3% compared to direct AP sintering-a gain comparable to the 30%-50% improvement typically achieved by direct HIP. Notably, the pre-HIP stage does not increase Ic degradation under stress; in fact, the tape's bending strain tolerance is slightly improved. This method was successfully applied to develop the first Ba-122 cable-in-conduit conductor, which fully retained the performance of the original tape. This confirms that the two-step heat treatment is a viable and cost-effective strategy for enhancing Ba-122 tape performance in large-scale applications.

The no-insulation (NI) magnets wound with REBCO coated conductors have thermal stability and quenching elasticity. This performance is driven by the current bypass on the interturn contacts. However, the resulting characteristic charging delay is controlled by complex electromechanical interactions in high magnetic fields, which are still difficult to predict. In this study, the contact resistivity of two 'sandwich' setups, namely 'No-Insulation Contact' and 'Metal-Insulation (MI) Contact', was investigated at 77 K and 4.2 K under pressure, specifically for copper-plated and copper-laminated tapes. A multi-exponential divergence model of contact resistivity with pressure is proposed to improve the fitting accuracy of the trend of contact resistivity with pressure. At the same time, the complete finite element method in the weak form of the T-A formulation is used to construct the simulation model of a large NI REBCO magnet based on a 2D axisymmetric coordinate system. The model directly calculates the inductance coupling through the magnetic vector potential, different from the field-circuit coupling model. This reduces the step of pre-calculating the huge mutual inductance matrix. Meanwhile, it incorporates electromechanical coupling by allowing the turn-to-turn contact resistivity (TTCR) to change dynamically in response to the instantaneous radial Lorentz force. It is verified on the ten-thousand-turn large-scale NI REBCO inserting magnet in the 35.1 T all-superconducting magnet system made by ASIPP. These results show that the charging behavior of the NI REBCO magnet in the high field is controlled by electromechanical coupling. Specifically, the Lorentz force alters the contact pressure distribution, leading to a spatially varying TTCR that determines the field stabilization time. This work provides key theoretical and model support for future electromagnetic-mechanical behavior prediction and quench robustness analysis of NI REBCO magnets.

The Comprehensive Research Facility for Fusion Technology (CRAFT) is a big platform dedicated to advancing key technologies and conducting performance tests on critical components of fusion energy reactors. It comprises 20 specialized test facilities and 4 auxiliary systems. Among these, the NDE (Non-Destructive Examination) laboratory is a sub-system of the SC (Superconducting) test facility, which is one of the 20 core facilities. The laboratory integrates phased array ultrasonic testing (PAUT, 0.5 MHz similar to 15 MHz), high-frequency acoustic microscopy (up to 100 MHz), digital radiography, and multi-scale X-ray computed tomography (micro-XCT up to 300 kV and high-penetration XCT up to 9 MeV). In addition, a dedicated cryogenic ultrasonic testing system has been developed, enabling defect inspection under temperatures ranging from -196 degrees C to 150 degrees C. Specialized NDE methodologies have been established for cable-in-conduit conductors (CICC), brazed joints in in-vessel components, and superconducting structural assemblies. Furthermore, an intelligent defect recognition algorithm based on a multi-round cross-modal attention mechanism has been implemented, achieving an accuracy of 99.25% in weld defect classification. The developed platform has been successfully applied in ITER, BEST, and CRAFT engineering projects, demonstrating its effectiveness in ensuring structural integrity and reliability of superconducting fusion components.

High-temperature superconducting (HTS) magnets are core components of China's next-generation fusion devices. However, the slow normal zone propagation velocity and the complex electromagnetic environment pose severe challenges to traditional voltage-based quench detection methods. This paper systematically investigates the application of distributed fiber-optic sensing (DFOS) based on optical frequency domain reflectometry technology in the quench detection of HTS model conductors. A model conductor incorporating REBCO CORC cables was designed and developed, and a specialized 'loose-tube' stainless steel capillary encapsulation process was employed to integrate the fiber-optic sensors. Experimental results demonstrate that this encapsulation scheme exhibits exceptionally high reliability, maintaining stable signal intensity and a high signal-to-noise ratio (SNR) during the cooling process from 293 K to 4.2 K. In various quench induction tests, the DFOS system showed excellent early warning capabilities: under the equivalent SNR criterion, its detection time was 0.3 s-2.2 s ahead of traditional voltage taps. Additionally, a significant baseline drift phenomenon was observed in repeatability experiments. Quantitative evaluation using the cooling time constant ( tau) revealed a notable thermal lag of the fiber compared to the conductor, with a maximum recovery ratio ( tau fiber/tau cond) reaching 7.37, which is primarily attributed to the thermal inertia of the helium layer inside the encapsulation. Based on these findings, engineering mitigation strategies are proposed, including the introduction of baseline recovery discrimination logic and the specification of mandatory reset times (e.g. > 19 min). This study provides critical performance benchmarks and technical guidance for the deployment of full-scale distributed fiber-optic systems in high-field HTS magnets.

To improve the mechanical properties of CORC cables in high-field magnets, a copper-tube reinforced CORC (R) cables have been developed. Although REBCO tapes have good flexibility and electromagnetic stability, they are highly sensitive to strain. Under bending loads, the strain generated on the tapes may exceed their allowable limits, leading to the critical current (Ic) degradation. To investigate the electromechanical performance of copper-tube-reinforced CORC (R) cables under bending loads, an equivalent bending finite element model was developed. Based on elastoplastic mechanics, the von Mises stress and strain of the copper-tube reinforced CORC (R) cables under different bending radii were investigated. The axial strain (epsilon axial) of the helical tapes was obtained through coordinate transformation. Then, by combining the calculated axial strain distribution with the experimentally calibrated axial strain-critical current relationship of the REBCO tapes, the relationship between bending radius and normalized critical current of the reinforced CORC (R) cables was established. The experimental results show that the critical bending radius of reinforced CORC (R) cables is approximately 125 mm, which is larger than that of traditional CORC cables. The strong agreement between simulation and experiment verifies the reliability of the finite element model in predicting the Ic decay behavior. The results provide guidance for the structural design and performance evaluation of fusion magnets in the future.

The selective removal of metallic stabilizers is a key segment for both the fabrication of superconducting joints and the surface characterization of the superconducting layer in REBCO-coated conductors (CCs). However, the REBCO is highly susceptible to chemical corrosion, and conventional wet etching techniques often induce irreversible degradation due to delamination of the superconducting layer. To address this challenge, this study presents a non-destructive electrochemical etching process. We successfully validated the application of this etching method on REBCO CCs fabricated using three distinct superconducting layer deposition techniques, achieving a single-pass etching length of up to 30 millimeters while fully preserving superconducting properties. Moreover, a hybrid process combining electrochemical etching and laser cutting was employed to successfully construct oxygen channels on the surface of the superconducting layer. This method not only produced a 20mm-long etched sample containing three oxygen channels but also achieved a critical current with virtually no degradation.

Rare-earth barium copper oxide (REBCO) coated conductors (CCs) are crucial for developing ultra-high field superconducting magnets required for next-generation applications. However, under ultra-high magnetic fields, the interaction between screening current and electromagnetic forces poses a challenge to mechanical stability. The presence of screening current leads to highly non-uniform current distribution and significantly increases local stress. This increase in local stress may exceed the irreversible strain limit of the REBCO CC, resulting in performance degradation or premature quenching. Therefore, efficient and accurate computational methods are needed to predict the behavior of high-temperature superconducting (HTS) magnets. This paper constructs a multi-field coupled analysis framework that rigorously considers the relationship between the critical current density (Jc) of REBCO tape and magnetic field strength, temperature, deflection angle, and mechanical strain. Furthermore, it integrates mechanical factors such as inter-turn contact mechanics, the elastoplastic constitutive behavior of structural materials, and winding prestress, enabling contact state analysis of thousands of turns of winding. The prediction results of this model have been experimentally validated on a 26.86 T magnet. The model shows that when local strain causes a decrease in the critical current Ic, the current distribution within the REBCO hoop redistributes. This inherent mechanism can alleviate the high stress problem caused by the screening current field to some extent. Therefore, using irreversible strain as the threshold for the mechanical operation of the magnet may be too conservative. Future stability assessments of high-field magnets require detailed analysis based on a multi-field coupling physical framework. Furthermore, the analysis shows that excessively high local electromagnetic forces under high magnetic fields can also lead to inter-turn separation, thereby reducing the radial shunting capacity of the uninsulated coils. This study emphasizes that improving the stability of the inter-turn contact is crucial for the reliable realization and maintenance of extremely high magnetic fields in future REBCO magnets.

Abstract Ba 1− x K x Fe 2 As 2 (Ba-122) is a promising material for high-field applications due to its high upper critical magnetic field, low anisotropy, and minimal performance degradation under high fields. Recent advancements in both short and long Ba-122 tapes have brought practical applications within reach. Traditionally, high-pressure sintering via hot isostatic pressing (HIP) or hot pressing is utilized to densify the superconducting core and enhance critical current ( I c ) performance. However, two major challenges hinder large-scale implementation: the high cost and technical complexity of large-scale HIP equipment, and the fact that Ba-122 becomes stress-sensitive after heat treatment, making the react-and-wind method impractical. To address these issues, we propose a two-step heat treatment method. In this process, the long tape is first coiled and subjected to a low-temperature pre-HIP stage in a compact HIP unit. Once the conductor or coil is formed, a subsequent atmospheric-pressure (AP) high-temperature sintering is performed. Experimental results show that this two-step process increases I c by 33.3% compared to direct AP sintering—a gain comparable to the 30%–50% improvement typically achieved by direct HIP. Notably, the pre-HIP stage does not increase I c degradation under stress; in fact, the tape’s bending strain tolerance is slightly improved. This method was successfully applied to develop the first Ba-122 cable-in-conduit conductor, which fully retained the performance of the original tape. This confirms that the two-step heat treatment is a viable and cost-effective strategy for enhancing Ba-122 tape performance in large-scale applications.

The development of high-field superconducting magnets for next-generation fusion devices requires robust, high-current cable-in-conduit conductors (CICCs) that withstand combined electromagnetic, thermal, and mechanical loads. In this work, a 2.8 m-long full-size prototype of a twisted stacked-tape rare-earth barium copper oxide (REBCO) CICC with a lateral support structure was designed, fabricated, and tested at the SULTAN facility. The prototype comprises three twisted stacked slotted-core sub-cables (336 REBCO tapes total), vacuum-solder consolidated onto a slotted copper former, wrapped with copper and 316 l tape and compacted into a CHSN01 stainless-steel jacket. Baseline tests at 77 K and self-field obtained a critical current (Ic) of 16.6 +/- 0.3 kA and an n-value of approximately 27. At a magnetic field of 10.85 T and operating currents of 60 kA and 70 kA, the measured current sharing temperature (Tcs) values were approximately 23.5 K and 19.6 K, respectively, deviating within 1.0 K of the predicted average for REBCO tapes. Under electromagnetic cycling conditions with currents reaching 75-80 kA and a background field of 10.85 T, the prototype exhibited only a 1.3% reduction in Tcs after the 53rd cycle, and remained stable throughout subsequent cycles, demonstrating excellent capability to withstand high-field electromagnetic loads. This represents the successful operation of a twisted stacked-tape conductor-type high-temperature superconducting (HTS) CICC under an electromagnetic load of similar to 830 kN & centerdot;m-1. The results confirm that vacuum soldering combined with a lateral support structure can effectively enhance the capability of HTS CICC to prevent the degradation under high transverse electromagnetic loads, providing crucial engineering experience for the future development of high-field HTS conductors for fusion magnet applications.

Iron-based superconductors (IBSs) are compelling candidates for high-field magnet applications due to their excellent intrinsic properties. The hot isostatic pressing (HIP) effectively enhances their critical current density by increasing core density. However, IBS tapes are highly stress-sensitive after heat treatment. This necessitates fabricating magnets prior to the HIP process. Consequently, the requirement for large-volume HIP furnaces for full-scale magnets presents significant technological and cost barriers. To circumvent this manufacturing bottleneck, this paper introduces a novel "pre-HIP" two-step annealing process. The principle involves an initial, low-temperature HIP (pre-HIP) heat treatment on IBS tapes to achieve densification. Subsequently, the tapes are wound into the desired magnet or conductor geometry, followed by a final heat treatment at atmospheric pressure (AP). This strategy allows large-scale magnets to be treated in conventional, cost-effective furnaces. We systematically evaluated the effect of the pre-HIP temperature (370-450 degrees C at 50 MPa) on the transport properties and bend performance of 7-filamentary Ba1-xKxFe2As2 (Ba-122) tapes. Results show that pre-HIP significantly enhances the critical current. However, a critical trade-off was identified: higher pre-HIP temperatures yield superior critical performance but induce local grain growth, causing severe degradation during bending. Samples pre-HIP at 370 degrees C retained 78 % of their initial performance after bending to 10 mm diameter, whereas the 450 degrees C samples degraded significantly. This study confirms that pre-HIP is a cost-effective method to improve IBS magnet performance when the optimal temperature is selected.

The use of High-Temperature Superconducting (HTS) technology in a fusion Central Solenoid (CS) magnet enables a significant enhancement in the inductive flux driving the plasma, achieved by increasing the magnetic field strength. This approach has garnered significant attention, leading Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) to join the research effort in designing and manufacturing a hybrid CS magnet that combines HTS and Low-Temperature Superconducting (LTS) coils. There is considerable mutual inductance between HTS and LTS coils, and their coupling can substantially affect the electromagnetic, mechanical, and thermal properties of hybrid CS magnet. Particularly, the quench of one or several coils can cause fluctuations in the performance parameters of the remaining coils, which is a critical issue in hybrid magnets that warrants further investigation. This paper analyzes and discusses the variations in electrical, magnetic, mechanical, and thermal parameters of the hybrid magnet following a quenching event, and offers reference insights for the design of such magnets from a stability-oriented perspective.

A smartly tunable bilayer composite achieves interlayer-complementary microwave dissipation for ultra-broadband absorption.

The central solenoid model coil (CSMC), developed by the Institute of Plasma Physics, Chinese Academy of Sciences, is designed to meet the engineering requirements of Chinese Fusion Engineering Testing Reactor (CFETR). The testing facility for the CSMC was established in 2023. Assembly of the coil was successfully completed in 2024, and the first round of testing was carried out on 29 December 2024. The second round of testing was successfully completed on 10 September 2025. To date, tests have been performed on hydraulic characteristics, insulation performance, including high-voltage and Paschen tests, joint resistance, operating current, fast discharge, AC loss, and current sharing temperature. These tests were conducted to verify whether the CSMC meets the design and engineering requirements for the CFETR project. During the testing, the model coil reached a steady-state operating current of 48 kA, exceeding the design value of 47.65 kA, and met the required magnetic-field ramp rate of 1.5 T s ^−1 , further demonstrating the coil’s stability and reliability under high current loads. This paper provides a detailed description of the testing facility, testing plan and execution process for the CSMC coil, and presents an analysis of the results of tests, including their implications for the future engineering design and application of CFETR. The test data and results offer valuable experimental support for the subsequent development and optimization of the engineering project.

Abstract High-temperature superconducting REBCO magnets are promising for high-field applications, but their inherently slow normal-zone propagation velocity poses a major challenge for quench detection and protection. Modulating inter-turn insulation to control current bypass and heat diffusion has emerged as an effective approach for improving coil stability. However, despite separate studies on representative inter-turn insulation strategies, their quench dynamics have not yet been directly and quantitatively compared under a common benchmark, which introduces uncertainty in interpreting differences in the underlying quench-dynamic mechanisms among insulation strategies and complicates the establishment of a common basis for insulation evaluation and quench-monitoring concepts. In this work, a 2D axisymmetric electromagnetic-thermal coupled model based on the continuum homogenization method is developed to investigate REBCO double-pancake coils with five inter-turn insulation configurations: conventional insulation, no insulation (NI), metal insulation, smart insulation (SI), and extremely no insulation (ENI). All coils are subjected to identical initial electromagnetic states and localized thermal disturbances. The unified comparison confirms the expected tendency toward stability among the five coils and further reveals insulation-dependent quench mechanisms beyond the minimum quench energy (MQE) ranking. NI and ENI coils exhibit strong disturbance tolerance, but their terminal-voltage signals may underestimate the severity of internal quenching because local resistive voltage is partially masked by electromagnetic diffusion and by induced voltage cancellation between pancakes. This indicates that enhanced self-protection does not necessarily imply improved detectability of voltage-based quenching. For SI coils, the metal–insulator-transition layer introduces a temperature-activated adaptive bypass process that reshapes quench dynamics rather than simply increasing the MQE. Lowering the transition temperature only slightly improves the MQE, but advances current redistribution, suppresses hotspot escalation earlier, and enlarges the protection-trigger time margin. These results indicate that inter-turn insulation strategies should be evaluated based on both thermal stability and voltage observability, rather than on MQE alone. This study provides a unified reference for understanding insulation-dependent quench dynamics and for informing future quench-monitoring and protection concepts in REBCO coils, while quantitative extrapolation to large application-level magnets requires further scale-up modeling and experimental validation.

Abstract The Beijing Spectrometer III (BESIII) is a particle physics experiment at the Beijing Electron–Positron Collider II (BEPCII) which aims to study physics in the tau-charm region precisely. Currently, the BESIII has collected unprecedented data, and the statistical uncertainty is reduced significantly. Therefore, systematic uncertainty is key for getting more precise results. In the BESIII, the measurement of energy deposition per unit length (so-called dE/dx) from the drift chamber is used for charged particle identification (PID) which is quite important for most analyses. Due to the Geant4 can not simulate the energy loss of charged particles in thin gas precisely, a sampling method using experimental data has been adopted for dE/dx simulation and it works smoothly. In order to further reduce the systematic uncertainty from dE/dx PID, an advanced machine learning method based on Normalizing Flows is studied for accurate dE/dx simulation, which shows quite promising results. In addition, due to the lack of understanding about dE/dx measurements at a very low βγ region, the expected dE/dx value and resolution can not be fitted well using the traditional method which decreases the dE/dx PID efficiency of protons(anti-protons) at low momentum region. To overcome the barrier, fully-connected neural networks are trained to accurately predict the expected dE/dx and its resolution. With this method, the dE/dx PID efficiency of protons(anti-protons) can be restored successfully.

This paper presents the design and experimental investigation of an epoxy-impregnated no-insulation (NI) yttrium barium copper oxide (YBCO) insert coil. The coil assembly consists of 8 stacked double-pancake (DP) coils with an inner winding diameter of 17 mm, incorporating 8 inner joints and 9 outer joints. The coils are impregnated using a method of vacuum pressure impregnation with epoxy resin (IR-3), replacing the support from over-banding in the hoop direction, and the maximum stress on the coil reaches 280.4 MPa. In order to strengthen the support in the axial direction and solidify the uniformity of the internal temperature of the insert coil, copper metal sheets are added between the DP coils. Finally, the insert coils are tested in a liquid helium environment, where the central magnetic field reaches 19.6T in a 10T background field when the operating current reaches 180A, and maintain stable operation for 15 minutes. This work can serve as a reference for the design and analysis of high-field epoxy-impregnated HTS insert magnets.