Experimental investigations on the stability of a He II cooled superconducting solenoid

Studies of the stability of a single layer superconducting solenoid are reported. In order to investigate various aspects of the stability of proposed designs, the solenoid is cooled with a concentric and confined layer of He II at 1.8 K and 0.1 MPa. Stability boundaries are measured for variety of types of thermal disturbances. It is found that these boundaries are insensitive to the duration of the thermal disturbances for disturbances less than 10 ms but are influenced by the spatial extent of those disturbances. A precipitous drop in the stability boundary at high currents is shown to be associated with the Kapitza resistance between the conductor and the liquid helium in agreement with existing theories. Results are presented on the development of normal zones in various conditions. These reveal spreading above a threshold of pulse energy density. Further, normal zone development in quench situations is shown to be useful in defining a relationship between the duration of the stability process and the joule heating of the conductor.