The design and development of highly stable Cable-in-Conduit Conductor (CICC) technology are of paramount importance to enable REBCO fusion magnets to operate in magnetic fields exceeding 20T. As part of the ongoing efforts to advance REBCO CICC, the technique of twist-forming plays a pivotal role in the fabrication process. It is instrumental in achieving uniform current distribution, enhancing conductor stability, improving the mechanical strength of the cable, and reducing AC losses. Consequently, ASIPP has designed and developed two distinct cable structures specifically tailored for superconducting conductors in future fusion devices. Structure 1 (three-in-one) involves the twist-forming process of three highly flexible REBCO Cable (HFRC) cables to form a multi-strand cable with different twist pitches. It is mainly suitable for small current conductors. Structure 2, the “six-around-one,” involves the precise twist-forming of six HFRC cables around a central hollow copper tube, resulting in the formation of a CICC cable. This structure is designed to cater to high-current conductor needs. Subsequently, their critical current performance with different twist pitches was experimentally evaluated under 77 K self-field conditions. The critical current test results indicate that for both structures, the critical current (Ic) remained around 335 A and 323 A as the twist-forming pitch decreased, with no significant performance degradation, respectively. This study preliminarily verifies the feasibility of the two twist-forming processes and demonstrates no significant influence on the cabling performance of REBCO cables with different twist pitches. These findings provide essential technical and parametric support for high-performance and full-size REBCO CICC production.

The ITER in-vessel coils are comprised of edge-localized mode (ELM) and vertical stabilization (VS) coils. There are 27 ELM coils and 2 VS coils. All the ELM and VS coils are supported by the clamped brackets bolted to the rails which are welded to the vacuum vessel wall. The in-vessel environment is severe, characterized by large transient electromagnetic fields, high radiation flux, and high temperature. Therefore, an appropriate nondestructive examination approach should be established and qualified. The difficulty in the development of the bracket weld nondestructive examination is the complex structure which brings space limit and various reflect echoes. Phased array ultrasonic test (PAUT) was studied and developed for nondestructive examination. In order to obtain the appropriate test parameters, CIVA simulation software was utilized to visualize the acoustic field distribution and coverage. The sensitivity of the PAUT method was also demonstrated by using machined defect provided by ITER Organization. Experiment results shows that all of reference defects can be detected with peak amplitude higher than 80% of FSH for both first leg and second leg.

The insulation system is an important part of the fusion magnet coils and its role is to mechanically support, insulate, fix, and protect superconducting magnets. The insulation materials used for the China Fusion Engineering Test Reactor (CFETR) Central Solenoid Model Coil (CSMC) are glass-fiber reinforced plastics. Internal defects may be generated in the composite insulation structure during manufacture or service life. The inspection of the composites has many difficulties, mainly due to the multiple interfaces and different elastic properties. This paper investigated the microstructure of the insulation system and defined the test objects for non-destructive test(NDE). Phased array ultrasonic test (PAUT) technology was developed to evaluate the integrity of the insulation system.

The Chinese Fusion Engineering Testing Reactor (CFETR) is aiming to bridge the gap between the International Thermonuclear Experimental Reactor (ITER) and the first commercial fusion power plant, a necessary complement of the ITER. The requirement for sustaining long burn duration as specified in the duty time CFETR mission necessitates the use of superconducting magnets. Totally 16 toroidal field (TF)D-shaped coils which are of cable-in-conduit conductor type are designed. All the subcomponents have very demanding requirement to withstand the severe environments. This paper gives the nondestructive examination (NDE) method developed for the jacket of TF conductor which is made of 316L stainless steel. Based on the linear elastic fracture mechanics, maximum acceptable defect sizes in the TF jacket material have been defined. Phased array ultrasonic testing(PAUT)method and eddy current test (ECT) method were developed for the circular-in-square jacket inspection. For PAUT method, focus laws were calculated and optimized. For ECT method, specific ECT probe was designed and manufactured. Benchmark experiments were carried out to study the NDE reliability.