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A pair of 1.5 kA current leads incorporating a conventional (copper) upper stage, a lower BSCCO stage, and intermediate cooling from a twin-cold-finger GM cryocooler have been designed, fabricated and tested. A lower stage has been fabricated and tested using a stacked-tape sample of BSCCO-2223 material donated by American Superconductor Corporation. Test results characterize the helium boil-off rate, cryocooler power consumed, and joint resistances measured during the base line operation of the current leads at various currents. Additionally, the transient performance of the leads in response to a loss of cooling is reported. Here the temperatures and voltage drops at significant locations on the leads are reported as a function of time for the various operation conditions. Test results show that the most significant factor in determining the allowable operation time subsequent to a loss of cooling is the thermal inertia of the cold bus connecting the current leads to the cryocooler. The current leads are designed for use in a /spl mu/SMES system and incorporate the necessary lead-to-lead voltage isolation within the body of the cryocooler.
Date of Publication: June 1997