Reliability of Bi-2223/AgAu Current Leads for Cryocooled Superconducting Magnet

Abstract

A current lead for a cryocooled superconducting magnet (CSM) was designed and fabricated using a high-temperature superconductor (HTS) tape, which could easily facilitate modification of the transport current capacity. The current lead was constructed of two terminal blocks, a support tube, and five Bi2223/AgAu HTS tapes. The Bi2223/AgAu HTS tapes with a critical current of 100 A at 77 K in self-fields were used for the current leads. The critical current value of the current lead was 390 A at 77 K in self-fields. The initial critical current at 77 K was maintained after four thermal cycles. The transport current of 170 A was continuously applied at 75 K, 0.27 T by conduction cooling. The voltage between two terminal blocks was 0.28 mV, even after 930 cycles of electromagnetic force (Lorentz force). The heat leakage through the current lead was 0.21 W from 55 K stage to 4.5 K stage. The experimental results showed that the current lead for CSM had sufficient strength against thermal stress and Lorentz force. The current lead has been operated in a CSM to demonstrate a stable excitation and reliability after thermal cycles from room temperature to 4 K. During the excitation and thermal cycle test, overall voltage of the current lead was maintained at an operational condition of 155 A, 55 K, and 0.26 T.