Cryogen free conduction cooled NbTi superconducting magnet for a X-band klystron

Superconducting magnet for a X-band klystron was designed, fabricated, and tested successfully. The magnet has a room temperature bore of 190 mm. The rated field is 0.7 T. 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 6 K and 30 W at 40 K 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 4 K, and the coil was energized without quench to 18.5 A which was 105% of rated current. The power consumption of 6 kW is 1/8 of the normal conducting magnet. The thermal leak of 0.2 W into the coil was measured, which was the same value of the design.