Liang Guo

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.

During the acceptance process of the central solenoid model coil (CSMC) for the China Fusion Engineering Test Reactor, a Paschen test is required to verify the reliability of the insulation structure. To locate insulation faults during magnet tests, this article presents the development of an insulation condition monitoring system (ICMS) based on visible light imaging technology. The ICMS first determines camera positions and lens types through field-of-view simulation, completing the hardware design of the system. The system software is then developed using mechanisms, such as multithreading and buffer zones, to realize online monitoring, offline detection, and fault location functions. To handle large volumes of image data, this article proposes a discharge image detection algorithm based on convolutional neural networks and image processing techniques, utilizing wavelet transform and attention mechanisms to enhance detection performance. The algorithm achieved an accuracy of 98.67% and an F1 score of 98.31%. The ICMS was validated during the CSMC Paschen experiment, with 21 cameras deployed for online monitoring, successfully capturing all discharge locations. After implementing insulation repair measures, the CSMC passed the Paschen test. The test results demonstrate that the ICMS can effectively monitor insulation status and locate breakdown discharge positions during CSMC testing, thereby ensuring the safe and stable operation of the magnet.

This paper primarily reports on the fabrication and testing results of a 16 T all-REBCO no-insulation (NI) magnet. The magnet is composed of 28 stacked double pancake (DP) coils, with a winding inner diameter of 112 mm and a cold bore diameter of 100 mm. Due to the length limitations of the REBCO tape, joints are required within the DP coils. The maximum stress on the coils reaches 399 MPa. The top and bottom DP coil of the magnet are wound with two REBCO tapes simultaneously to improve the electromagnetic margin. To prevent degradation of the joints under stress, we have designed the joint to be located in the low-stress regions on the outer turns of the coils. The magnet contains a total of 76 joints, of which 49 are lap joints located internally within the DP coils, while 27 are splice joints situated between the DP coils. Finally, the magnet was tested under 4.2 K conditions. When the operating current (I_op) reached 252.3 A, the measured central magnetic field of the magnet reached 16.2 T and maintained stable operation for 30 minutes.

The Central Solenoid Model Coil (CSMC) has been manufactured and assembled as part of the R&D projects for the China Fusion Engineering Test Reactor (CFETR), and will be tested at ASIPP. The measurement of the current sharing temperature (T_cs) of the coil at maximum operating current of 47.65 kA is proposed to assess the performance of the coil. The T_cs is defined as the point where the electric field locally reaches 10 μV/m. During the T_cs test, voltage taps measure the voltage of each cooling channel of the CSMC. Reliable thermal-hydraulic predictions are necessary to estimate the total voltage across a cooling channel when the local electric field is 10 μV/m, supporting the definition of the T_cs loop heating strategy. A predictive analysis of the T_cs tests for the CSMC is carried out, using the GANDALF code. An optimum heating scenario, based on the staircase strategy is developed to reduce cryogenic costs.

Magnet performance research platform is an important scientific research device for testing the physical properties of superconducting magnets, and the support structure is an essential supporting and bearing component of the magnet performance research platform, which plays a role in carrying and protecting the magnets. In order to ensure the safety of magnet testing, the mechanical strength analysis of the support structure is imperative. This paper carries out numerical analysis of the structural mechanical strength of the support structure under room temperature, cryogenic temperature, seismic load conditions. The maximum equivalent stress of the support structure under the three working conditions is 94.7 MPa, 103.2 MPa, and 131 MPa,respetively. The calculation results show that the support structure meets the engineering design requirements .

The Central Solenoid Model Coil (CSMC) has been manufactured as part of the R&D projects for the China Fusion Engineering Test Reactor (CFETR), and it will undergo testing in the second half of 2024. For the safety operation of magnet, predictive analyses are required to study thermal-hydraulic behavior of the CSMC during the quench. In this paper, the different quench initial position is detailed studied, for example, quench initiates at the peak magnetic field region and the lowest magnetic field region. In addition, the different quench disturbances are considered, such as (disturber length 0.01 m and disturber time 3 ms), (disturber length 1 m and disturber time 3 ms), and (disturber length 6 m and disturber time 100 ms). In all cases, the designed quench protection system is satisfied with the present design criteria concerning the hot spot temperature and the maximum helium pressure.

A large-scale superconducting magnet cryogenic performance research platform is being built in China to perform the large-scale superconducting magnet research on mechanics, thermology and electromagnetics properties and evaluate the superconducting magnet system compatibility, reliability and stability. Performance research platform has an oversized test space whose dimension is 24 m × 15 m × 6.5 m, including a pair of the high temperature superconducting current lead with current carrying capacity of 100 kA. Cryogenic system of the performance research platform can provide the supercritical helium of mass-flow about 700 g/s at 3--6 bars. The detection accuracy of the quench detection and protection system can reach 99.99%. Performance research platform will be utilized for superconducting magnet tests, such as DC hipot test, helium leakage, Paschen test, maximum operation current test, joint resistance, Tcs test and Fast discharge test.

A 20 T all REBCO conduction-cooled user magnet project is underway by Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The REBCO magnet with no-insulation (NI) winding technique has the inner and outer winding diameters of 30 mm and 103.98 mm, respectively, and the diameter of the cold-bore is 22 mm. It consists of a stack of 10 double pancake (DP) coils wound with two different width REBCO tapes, the width of REBCO tape used for the two end double pancake is 6 mm, and the remaining DP coils is 4 mm. The operating current of the magnet is 224 A at 10 K. The inductance, maximum hoop stress and deflection angle between the conductor and z-axis are 1.57 H, 583 MPa and 1.41°, respectively. The magnetic field distortion and local stress concentration caused by screening current have been carefully considered. In addition, the electromagnetic design and parameter optimization, mechanical analysis, construction and preliminary test results of DP coils are specially discussed in this article.