Measurements of retractable gas-cooled 6061 aluminum electrical leads operating in a vacuum

To charge and discharge the ASTROMAG superconducting magnet in space requires retractable gas-cooled leads which must operate in a vacuum. This report describes the design and test of 500 ampere retractable gas-cooled leads made from 6061-T4 aluminum tubes. Aluminum is attractive for gas-cooled electrical leads in space because of its low mass density and the desire for short leads. Initial tests showed that retractable gas-cooled leads could operate in a vacuum from a source of normal helium. The pressure drop through the leads was low enough to permit a superconducting magnet to be charged and discharged while the leads vent into space. The leads were stable at currents above 700 amperes. The voltage drop across the contact between the upper and lower leads was as low as 1.2 mV per lead out of a total voltage drop of 42 mV per lead when the leads carried 714 amperes. The gas required for cooling was comparable to the more conventional copper gas-cooled current leads. In a second test seven months later, the contact resistance between the lead sections had increased considerably. In the second test, the contact resistance was repeatable for one lead but not for the other.