Cryogen free operation of a niobium-tin magnet using a two-stage pulse tube cooler

A conductively cooled superconducting Nb/sub 3/Sn magnet system has been designed and tested that employs a two-stage 4 K pulse tube cooler. The Nb/sub 3/Sn coil has a clear bore of 11 mm and a mass of 2.6 kg. High-T/sub c/ current leads are used to reduce the heat leak to the 4 K stage. After a cooling time of about six hours the 2nd stage and the magnet surface attained stationary temperatures of 3.4 K, and 4.1 K, respectively. The 1st stage cold head was then at 54 K. The magnet coil was repeatedly charged with a current of 120 A corresponding to a central field of 2.8 T. Stable operation of the energized system has been demonstrated for 25 hours.