Superconducting solenoid and its cooling system for pulsed muon channel

A large superconducting solenoid and on-line cooling system was constructed for π-μ decay section in a pulsed muon channel at the KEK Booster Synchrotron. Its dimension is 12 cm bore and 6 m length and the central field is 5 T. Following the design taken at SIN, the solenoid is indirectly cooled by a forced flow of supercritical He. The important features of our system are as follows : 1) The supercritical He is produced by a heat exchanger built inside the cold box (single SHE exchanger) simplifying cryostat design and system control ; 2) Magnet cryostat has warm-iron structure as a vacuum wall with LN2shield. The system has been operational for more than 1500 h since July 1980. The paper describes conceptual designs, some details of construction and performances of the system.