Cyclic load effect on round strands made by twisted stacks of HTS tapes

Highlights: • Investigation of the cyclic load degradation in the HTS cable prototype is performed. • Results of transverse load fatigue tests on the HTS strands at 77 K are presented. • Design of the new HTS cable prototype for the DEMO CS coils is discussed. - Abstract: Various DC tests performed recently with full-size 60 kA HTS cable prototypes in the EDIPO test facility demonstrated that proposed design of HTS strand at Swiss Plasma Center (SPC) – stack of HTS tapes twisted and soldered between two copper profiles – is applicable for high-current fusion cables, but improvement of the strand mechanical properties against the cyclic loading is still needed. Based on experimentally obtained correlation between the performances of cable prototypes at different operating conditions, further investigation of cyclic transverse load on the strand performance was performed at 77 K. Aiming to obtain a strand design able to withstand a continuous cyclic load operation of some thousand cycles, influence of the strand geometry and tape's manufacturer has been studied. Cyclic load has been applied up to 1000 cycles for straight and bent samples at the load amplitudes up to 4 MPa. Based on the obtained data, next design of HTS cable prototype will be discussed.