Flow instabilities in gas-cooled cryogenic current leads

Gas-cooled cryogenic electric current leads which are operating at high ratios of current to mass flow are commonly used to supply electric current to superconducting magnets. Loss of coolant flow under such operating conditions will result in destruction of the lead and possible damage to the magnet itself. A flow instability, which results in loss of coolant flow, can occur in current leads due to the dependence of the kinematic viscosity of the coolant on the local temperature. This paper discusses the physical basis of the instability and presents an analysis which is used to describe the operation of current leads used in the EPRI-MIT 2000 kVA superconducting alternator. Details of the lead design and test results are included.