A High Tc Superconducting Current Lead Assembly for the XDS Helium Cryostat

Abstract

The X-ray Spectrometer Detector System (XDS) helium cryostat consists of a tank of pumped liquid helium at about 1.3 kelvin suspended inside a seventeen kelvin cylindrical support structure. The tank is a heat sink for an adiabatic demagnetization refrigerator (ADR) and its superconducting magnet. The cryostat’s small initial helium volume and mission lifetime goal of 2.5 years require that the average total heat load to the helium be less than about 800 microwatts. During the mission the superconducting magnet requires a current of 2 amps with a three percent duty cycle. In addition, wires capable of carrying up to 1 amp are needed for cryogenic valve operations during the cryostat’s ground servicing. The best optimized conventional current leads between the 17 kelvin stage and the magnet and valves would contribute an average heat load to the helium of about 3 milliwatts. An assembly of superconducting YBaCuO fibers bonded to a fiberglass tube and suspended by a Kevlar* braid was developed to conduct the current from the 17 kelvin support structure to a vapor-cooled 4 kelvin stage. NbTi wires provide a superconducting path from the 4 kelvin stage to the magnet and valves on the 1.3 kelvin helium tank. This paper describes the assembly’s fabrication and suspension and presents the results of its performance and vibration tests.