Study on Influence of Repeated Hoop Stresses on HTS Wires in Coils

HTS wires in coils are subjected to hoop stresses due to electro magnetic forces and thermal contractions. Influence of repeated and non-repeated hoop stresses is investigated by making an experimental apparatus to apply hoop stresses mechanically to dry (non impregnated) and epoxy-impregnated HTS test coils. In the experiment it was found that a critical current of a dry coil was more degraded by the hoop stresses than that of an epoxy-impregnated coil. In the paper, distribution of hoop stresses to layers in HTS coils are investigated and based on the experimental results, differences of critical current degradations of dry and impregnated coils are studied.