Design of a Helium-Free Test Cryostat for Superconducting Wires, Cables, and Windings

A helium-free test cryostat is being built to support testing of superconducting wires, cables, and windings. Three cryocoolers are mounted on the top hat of an LN2-shielded open-top cryostat and used to heat-sink thermal intercept shells at 50 K, 20 K, and 4.2 K. Ternary leads are used for supply and return of a 10 kA circuit (for a background-field dipole) and a 20 kA circuit for a test sample. Each lead is a series connection of a N-2 vapor-cooled lead and a Bi-2223 Type G lead. A closed-flow liquid helium loop is used to maintain the Nb3Sn CIC windings of a 10 T background field dipole at 5 K. The objective of the design is to make it possible to sustain the test environment relying solely on LN2 and three cryocoolers, without the expense of a helium liquefier or a large inventory of liquid helium.