Cryogenic tests of glass-epoxy based electrical insulation

A thin superconducting solenoid for the Time Projection Chamber (TPC) experiment was constructed and tested. A failure of the ground plane insulation damaged the coil to the point that it required rebuilding. An extensive study of this failure indicated that an iron chip embedded in the bore tube had penetrated the insulation. Before rebuilding the coil, an investigation of the insulation system was done with the goal of determining the most reliable techniques and materials for withstanding high voltages in the coil package. The experience with the TPC coil and its prototypes indicate that glass cloth vacuum-impregnated with epoxy is an excellent material for cryogenic applications from the mechanical standpoint. The investigation concentrated on different types of glass cloth and on composites containing glass cloth.