1.7 K—1000 A Critical Current Measuring Holder Using YBa2Cu3O7 Current Leads

In order to evaluate large transport critical currents in a superfluid helium bath at 1.8 K, we made an easy-operational critical current measuring holder with YBa2Cu3O7 current leads. An YBa2Cu3O7 current lead covered with a FRP sheath, which has a 1500 A current capacity at 77 K and 4 T for B // c-axis, was fabricated by a melt-textured growth technique. A thermal input of a pair of 1500 A FRP/YBa2Cu3O7 current leads was reduced less than 0.74 W. When a pumping speed of 3000 l/min. was applied for liquid helium evacuation using a newly developed sample holder, the temperature was lowered from 4.2 K down to 1.6 K in about 25 min. We performed to carry transport currents up to 1020 A at 1.7 K. The temperature rise of a superfluid helium bath was less than 0.1 K at 1.6 K, during measuring the critical current of 1000 A.