YBCO current leads for adiabatic demagnetization refrigeration of X-ray detectors in space

Future satellite missions carrying X-ray spectrometers will be cooled to milliKelvin temperatures by multistage Adiabatic Demagnetization Refrigerators (ADR), which, in turn will be precooled by closed-cycle cryocoolers. Each stage of the ADR will use a low temperature superconducting magnet, which will periodically be energized via high temperature superconducting (HTS) leads. The heat-leak and required refrigeration for these leads has historically been a relatively large burden on the mission energy budget; hence the motivation for a lower heat leak. Our suggested approach is to fabricate inherently tough and flexible leads in the 2A to 10A range from commercially available YBa₂Cu₃O_7-X (YBCO) tape. The substrates of such tapes are tough, strong, low thermal conductivity metals which can be cut longitudinally into thin strips approximately 500 micrometers in width using a precision dicing saw. In the region of the thermal gradient, the protective silver coating is removed and replaced by a non-conducting encapsulant; the as-manufactured silver coating is left at the ends to make electrical joints. This is a process which should lend itself well to small-scale manufacture. We have demonstrated the feasibility of several key facets of the design and expect that the overall result of this project will be to reduce significantly the size, weight and power requirement of the satellite-borne cryosystem and at the same time produce a lighter more robust lead structure.