Operating experience with ESCAR magnet cooling system

The ESCAR magnet cooling system has been successfully demonstrated. This two-phase helium cooling system includes a CTI-Sulzer gas-bearing turbine refrigerator with two-stage compression by oil-lubricated screw compressors, 120 m of 5-cm-diameter vacuum-insulated transfer line and twelve series-connected magnet cryostats with weirs for liquid level control. The refrigeration plant provides up to 1900 w of refrigeration at 4.5 K with a mass flow of 113 g/s. Heat load within the transfer line has been measured at 0.25 w/m in sub-system testing. Cool-down times to 4.5 K for the 12 warm-iron magnets with a cold mass of 2500 kg have been about 12 hours. The magnet cryostats separate the liquid by gravitational extraction and fill in sequence at a rate of up to 400 l/hr. A heater in the transfer line allows adjustment of the inlet coolant quality (ratio of gas to liquid) to the cryostats. Pressure levels in the cold bore, beam orbit space were below -10 torr