Performance test and analysis of the first large-scale cable-in-conduit conductor with high J _c Nb₃Sn strand for fusion reactor

Abstract

The Comprehensive Research Facility for Fusion Technology (CRAFT) project has been launched in 2019, for developing the essential engineering technologies for Chinese Fusion Engineering Testing Reactor (CFETR). Within this project, a full-size toroidal field (TF) coil will be built as the prototype coil for CFETR. Based on design of CFETR magnet system, the TF coil will operate at 95.6 kA in a peak field of 14.5 T. The high-J c Nb3Sn strand is taken into consideration due to the critical current density of ITER-grade Nb3Sn is too low at 14.5 T. Considering that it will be the first time to apply the high-J c Nb3Sn strand in the large-scale cable-in-conduit conductor (CICC) for fusion magnet, a conductor sample made of high-J c Nb3Sn strand with short twist pitch (STP) cable pattern was manufactured in ASIPP and tested in SULTAN facility, to investigate the feasibility. The test campaign focuses on the impact of cyclic electromagnetic (EM) loading and warm-up cool-down (WUCD) to the performance of the conductor, the strain distribution of the conductor before and after EM cycles was measured by inductive method to make a deeper insight of the conductor performance evolution. AC losses tests have also been carried out, providing relevant information for further coil design.

Mechanical effects: challenges for high-field superconducting magnets

“…For example, short-pitch (STP) cable in conduit conductors (CICC) exhibit excellent characteristics of inhibiting shunt temperature degradation under cyclic electromagnetic loads. This conclusion has been validated by SULTAN’s experiment [ 10 ] and the theoretical prediction given by Lanzhou University [ 11 ]. Therefore, STP-type conductors will also become the first choice for national CFETR high-field coils.…”

High performance of an innovative cable-in-conduit conductor with CWS cable pattern

“…The area where the two legs are in close to each other will reach the maximum magnetic field. Therefore, the conductors generate a self-induced magnetic field during electromagnetic testing, which adds to the background magnetic field into forming the final magnetic field [25,47]. The magnetic field in total was calculated by:…”

“…However, since Nb 3 Sn is a brittle and strain sensitive material, serious degradation of the T cs of Nb 3 Sn CICCs were observed under cyclic electromagnetic load. After a series of investigations on performance degradation of CICCs under high Lorentz force, fracture of superconducting Nb 3 Sn filaments inside strands were found to be the main reason [24][25][26][27][28][29][30].…”