Development of quench protection heaters for superconducting solenoids

Our approach to applying quench heaters to epoxy impregnated coils is to encapsulate the heaters within the epoxy and glass on the coil circumference. The mechanical integrity of the epoxy and glass in the neighbourhood of the heater is critical. The interface is subject to large temperature gradients and mechanical stress during operation of the protection system. Characterization of this interface allows the reliable design of heater networks on large epoxy impregnated coils. The heater is a thin stainless steel strip located axially on the outside of the coil. The geometry may be further complicated by the presence of steel over-banding on the coil perimeter. We have fabricated models demonstrating heater interfaces with and without overbanding. We characterize the interface using a damage threshold concept in the context of cyclic life testing on the interface. This paper reports the results from cyclic life testing in liquid helium.