System for warming-up and cooling-down a superconducting magnet

A method of servicing a target object disposed in a target object cryostat using a service system, the target object cryostat having a supply port for receiving cold gas during cool down and a return port, the service system comprising:

• one or more expanders and one or more compressors for cooling-down the target object to a cryogenic temperature;
• one or more heaters for warming-up the target object from the cryogenic temperature;
• a fan and a fan circuit, the fan circulating gas through the fan circuit;
• and
• a refrigerator cryostat housing the one or more expanders and the fan which are surrounded by a vacuum;
• a plurality of heat exchangers for transferring heat from the heater to the gas in the fan circuit during warm-up of the target object and for transferring heat from the target object to the gas in the fan circuit during cool-down of the target object;
• a controller and a plurality of sensors, the plurality of sensors for measuring a temperature and a pressure in the fan circuit, the controller responsive to the plurality of sensors controlling at least a speed of the fan, a speed of the expander, and a power of the heaters;
• a removable supply transfer line for bringing gas from the fan circuit to the target object cryostat;
• a removable return transfer line for returning gas from the target object to the fan circuit, the transfer lines being interchangeably connected to the target object cryostat;
• a pressure relief valve for relieving excess pressure in the fan circuit;
• and
• a vent valve that can be actuated to open to one of atmospheric pressure and a gas recovery system;
• the method comprising the steps of:
• (a) inserting proximal ends of the transfer lines in the refrigerator cryostat,
• (b) capping distal ends of the transfer lines,
• (c) evacuating then filling the fan circuit in the refrigerator cryostat and transfer lines with the cryogen disposed in the target object cryostat,
• (d) maintaining a purge with the same cryogen as in step (c) while connecting the return transfer line to a supply port in the target object cryostat,
• (e) maintaining a purge with the same cryogen as step (c) while connecting the supply transfer line to a return port in the target object cryostat,
• (f) opening the vent valve,
• (g) increasing the fan speed then controlling it such that gas does not vent through the relief valve,
• (h) controlling fan speed and heater power to warm the target object, and
• (i) removing said supply and return transfer lines from said target object cryostat.