Performance measurements of superconducting current leads with low helium boil-off rates

A performance-measurement facility for current leads has been developed as a part of Argonne National Laboratory´s program to develop applications for high-temperature superconductors. The facility measures the rate of helium vapor boil-off due to current-lead heat input to liquid helium and the pressure drop across a current lead for a pair of leads operating at currents up to 100 A. The facility´s major components are a liquid-helium dewar with low background-heat input; a dewar insert that incorporates the current leads and associated instrumentation or connections for flow, pressure, level, temperature, and voltage measurements; and a computer-driven data-acquisition system. Background heat input is low enough so that boil-off rates one-tenth that of an optimized conventional lead can be characterized. The facility has been operated with conventional leads, and with leads incorporating high-temperature superconductors at their cold ends. Details of the facility design, construction, and operating experience are presented.<>