Report on Over 25 000 Cycles Fatigue Test Results of a REBCO HTS Coil and Crossover Joint in a 7 T Background Magnetic Field at 4.2 K

This study presents experimental results on the fatigue characteristics of a REBCO coil and crossover joint, aiming to determine whether they can withstand cyclic loading up to the condition of the 40 T superconducting magnet's design fatigue limit. A pair of REBCO coils were wound with SP (SuperPower) 1013, using copper and stainless steel tape as co-winding materials. The crossover sample, designed to the 40 T superconducting magnet baseline specifications and composed of four Bi2223 (Sumitomo Type H) tape conductors soldered to a stainless steel foil, was mounted to the outermost turn of the REBCO coil. Both the coil and crossover were subjected to cyclic loading by ramping the current up and down in a 7 T background magnetic (BM) field at 4.2 K, with over 25,000 cycles applied. The electromagnetic strain between the outermost turn of the REBCO coil and the crossover joint was estimated numerically, considering the screening current distribution.