AC loss measurements with a cryocooled sample

A new cryostat cooled by a closed-cycle Cryomech GB-37 cryocooler for super conductor measurements at temperatures down to 20 K is described. The sampl e is conductively coupled to the cold stage so as to minimize vibration and thermal stresses. AC losses have been measured calorimetrically in several high-temperature superconductors coils that have been wound to simulate su bscale transformer winding pairs. Stable temperatures down to 20 K were rea ched on these coils, allowing measurements at practical levels of ac curren t and I-c. By using short ac current pulses, losses on individual turns cou ld be resolved. Results are reported mainly to showcase the apparatus, meas urement procedure, and analytical approach.