DC performance measurement and assessment of Nb3Sn Cable-In-Conduit Conductor for CFETR CS model coil

The Central Solenoid Model Coil (CSMC) project of China Fusion Engineering Test Reactor (CFETR) was developed from 2014 at the Institute of Plasma and Physics Chinese Academy of Sciences (ASIPP) to verify the larger-scale superconducting magnet technology. The short twist pitch (STP) option was chosen for Nb3Sn Cable-In-Conduit Conductors (CICC) due to the stronger rigidity which can withstand the higher electromagnetic (EM) cycles effectively. Performance measurement of conductor short samples in SULTAN facility is the most important assessment method. This paper introduces the Nb3Sn strand parameters and CICC design firstly; then the preparation and measurement procedure of conductor short samples for current sharing temperature (Tcs) are described; subsequently, the Tcs vs. cycles, effective strain (εeff) with B × I and transition broadness characteristics compared with strands are assessed qualitatively by power law model. The assessment result shows that the DC performance vs. cycles of the STP design for Nb3Sn CICC is very stable and no degradation. The notable result gives the confidence that life period in the CSMC can be achieved reliably although the number of the EM cycles has been limited to below 10 000 in the measurement. The successful DC performance testing of Nb3Sn CICC will be an important milestone for CSMC project. Lastly, the performance assessment in coil is performed at the typical test waveform. The minimum temperature margin (Tmag) of 0.14 K and electric field of 5 uV/m are achieved respectively. Some slow EM cycles is required to decrease the coupling loss deposition before coil testing.