Stabilization of large superconducting magnets in superfluid helium

Stability of large superconducting magnets cooled with superfluid helium (He II) is examined. Impetus for this research is the Wisconsin Superconductive Energy Storage magnet system, which proposes to be operated at 1.8 K. A survey of steady state heat transfer in He II is presented in the context of magnet stability. In addition, new results from an experiment to study the transient response of He II show substantially better heat transfer than that of normal helium (He I). For example, a step-function application of heat flux at a rate of 2 W/cm²can be absorbed by the helium for about five seconds before film boiling begins. This time delay is caused by the required temperature rise of the He II adjacent to the hot spot. A comparison between the enthalpy rise in the helium and the applied energy shows a close correlation. These new results are discussed in terms of superconducting magnet stability.