CRITICAL-CURRENT MEASUREMENT UNIT UTILIZING BI-BASED OXIDE SUPERCONDUCTING CURRENT LEADS AND CRYOCOOLERS

A measurement unit has been developed to investigate the dependence on temperature and magnetic field of critical current without the use li quid helium or liquid nitrogen. A test specimen, which is tested using the four probe method, is cooled by a Gifford-McMahon(GM) type Cryoco oler to a temperature of 20 K to 90 K in a vacuum vessel. Transporting direct current, up to 500 A, is supplied to the specimen through the Bi-based pride superconducting current leads. The advantages of utiliz ing oxide superconducting current leads are that the leads have low th ermal conductivity, and also that the leads create no Joule heating ef fect, so the heat input to the sample is minimized. The external magne tic filed of up to 3 T, which is applied to the specimen, is generated by a superconducting magnet which also uses Bi-based oxide supercondu cting current leads and is also cooled by a GM cryocooler. Detail desi gn of the unit, the results of operating test and an example of the me asurement result on the Bi-based oxide bulk specimen are presented in the paper.