Bolometric measurement of ac loss in HTS tapes: a novel approach of microwatt sensitivity

Measurements of ac loss on superconducting tapes are important, but non-tri vial. It is well known that in the potential tap method the ac voltage cont ains a large reactive component, and that its magnitude depends upon the cu rrent distribution and the position of the voltage contacts; these are part icularly uncertain in multi-filamentary conductors. Bolometric measurements of ac loss are intrinsically more reliable, but previous approaches have r equired long lengths (similar to 1 m) of conductor, which introduces other complications. We describe a novel bolometric technique that measures ac lo sses of HTS tape samples only a few centimetres in length. It has a sensiti vity approaching 10(-4) W m(-1), and can be used over a wide frequency rang e; a single measurement can be taken in 1 min or less. It may be adapted fo r measurements of short-sample losses in the presence also of an ac magneti c field.