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

A conductively cooled superconducting Nb3Sn magnet system has been designed and tested that employs a two-stage 4 K pulse tube cooler. The Nb3Sn coil has a clear bore of 11 mm and a mass of 2.6 kg, High-T-c current leads are used to reduce the heat leak to the 4 K stage. After a cooling time of abou t six hours the 2(nd) stage and the magnet surface attained stationary temp eratures of 3.4 K, and 4.1 K, respectively. The 1(st) stage cold head was t hen 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 energiz ed system has been demonstrated for 25 hours.