Specifications and performance experience of pool boiling cooled magnets

Abstract

Large superconducting magnets have three kinds of conductor-cooling methods; liquid helium pool boiling cooling, two-phase helium indirect cooling, or supercritical helium internal cooling. Practical superconducting magnets in their thirty years' history have had a lot of failure experiences. Electrical breakdown of insulation is the most fatal for pool boiling cooled magnets, because those magnets are unable to be utilized again, unlike quenched magnets. The insulation design of the coil winding is one of the most important key points for a pool boiling cooled magnet, where the coil protection conditions need to be considered. They are the maximum temperature rise at a quench and the maximum voltage at current interruption. In this paper, an overview of magnet insulation design, the introduction of stored energy scaling law on rated coil current, and the engineering contents of helical coils assembled into the Large Helical Device and excited in March 1998 as an example of insulation design are described.