Magnet

The ESCAR magnet cooling system has been success fully demonstrated. This two-phase helium cooling system includes a CTI-Sulzer gas-bearing turbine refrigerator with two-stage compression by oil- '1 ubri cated screw compressors, 120 m of 5-cm-d i ameter 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 liquid by gravitational extraction and fill in sequence at a rate of up to 400 ~/hr. A heater in the transfer line allows adjustment of the inlet coolant quality (ratio of gas to liquid) to the cryostats; flow instabilities were not present and could not be induced. Pressure levels in the cold bore, beam orbit space were below 10-10 torr. result of magnet transitions, have been safely handled both in terms of refrigerator response and cryostat pressure relief. have