Superconducting focusing solenoid for X-band klystron

A superconducting focusing solenoid for X-band klystron has been developed. The system consists of a conduction cooled NbTi solenoid, high T/sub c/ superconductor current leads, and a GM refrigerator. The GM refrigerator can cool down the solenoid from the room temperature to below 4 Kelvin by 4 days. This allow us to operate the system without supplying any cryogen such as liquid helium or nitrogen. The solenoid produces a desired field profile whose maximum value is about 7 kGauss. A normal conducting bucking coil is also implemented in order to tune the field at the cathode. Cool down tests performed at MELCO, KEK, and SLAC confirmed that the system can be cooled down by 4 days. Field measurements performed at those places confirmed that the field profile is very stable between thermal cycles.