Liquid He Free Conduction Cooled Superconducting Magnet for a X-band Klystron

Abstract

A liquid He free conduction cooled NbTi superconducting magnet for X-band klystron was designed, fabricated, and tested successfully. The magnet has a room temperature bore of 190 mm. The rated field is 0.7T. In order to meet the requested magnetic field distribution, the NbTi coil is separated to three parts and a return yoke is set. The coil is cooled by a two-stage Gifford-McMahon cycle refrigerator. The refrigeration capacity is 1.1 W at 6K and 30W at 40K for each stage. Current leads are made of 2223 Bi-based oxide superconductor. The coil was cooled down to superconducting state from room temperature in 85 hours. The ultimate temperature of the coil was below 4K, and the coil was energized without quench to 18.5 A which was 105% of rated current. The power consumption of 6kW is 1/8 of the normal conducting magnet. The thermal leak of 0.2W into the coil was measured, which was the same value of the design.