Alternating Current Losses in Thin Film Superconductors: New Calorimetric Measurement Technique

A calorimetric technique has been developed for measuring the ac loss in short, cylindrical thin film superconductors carrying a transport current. Substrates used in the present study were 0.32 cm in diameter by 3.8 cm long. Loss in the range 10−8−10−4 W may be determined by measuring the temperature rise at the center of the sample, which causes a decrease in resistance of a carbon resistance thermometer mounted inside the hollow cylindrical substrate on which the superconductor is deposited. By maintaining the current contacts at 4.2 K and heating the center of the sample (in a vacuum can), loss may be determined from 4.2 K up to the transition temperature of the superconductor. Data below 4.2 K are taken by lowering the temperature of the coolant bath. This technique has been used extensively to study the temperature dependent ac properties of Nb3Sn. Typical loss data are shown.