Basic characteristic evaluation of cryocooler-cooled HTS coils

To survey the applicability of existing HTS wires for SMES, five kinds of cryocooler-cooled HTS coils were fabricated and tested to estimate fundamental characteristics of HTS wires. Critical current, run-away current, and ac losses were measured. To confirm the effect of electromagnetic force to the coil performances, critical currents were measured under high magnetic fleld of 14 T with liquid helium cooling. The HTS wires used for the coils are three types of Bi2212 wire and two types of Bi2223 wires. We have wound these wires to little coils of 14 cm outside diameter, 10 cm height with cryocooling. As a result, a difference of critical current characteristic of a Bi2212 wire and a Bi2223 wire was not big at the temperature of 20 K, but a critical current of a Bi2212 wire fell at 50 K greatly, and the HTS-SMES design that utilized a temperature margin by cryocooler-cooled system understood what a Bi2223 wire was suited for.