Thermal characteristics of the magcool cryogenic system after quenches of RHIC dipoles

Thermal characteristics of the MAGCOOL cryogenic system after both natural and heater-induced quenches of the RHIC dipoles have been investigated. For natural quench currents around 6700 amperes, the pressure in the cooling loop exceeded the 15 atmosphere (15.2 MPa) setting of the quench relief valve causing helium to vent through the valve. The initial pressure rise rate was approximately 18 atm/min and the loop pressure increased from 5 to 15 atm in about 30 seconds. To ensure that no helium was vented from the MAGCOOL cooling loop in order to minimize uncertainties in the thermal measurements and better understand the heating/cooling process, the RHIC magnet was then quenched at lower currents between 2000 and 5000 amperes using a strip heater on the magnet coils. A series of tests with the cooling loop connected to a large volume surge tank was also performed to show the dependence of loop pressure on the loop volume. The peak pressure and temperature in the magnet cooling loop were found to be linearly proportional to the energy released for a given loop volume. The time lag of temperature along the cooling loop during quench recovery was determined. Very good agreement between total cooling provided and the magnetic stored energy was found for each of the several values of quench current