Determination of the AC losses of Bi-2223 HTS coils at 77 K at power frequencies using a mass boil-off calorimetric technique

A mass boil-off measurement system has been used to accurately measure and characterize the ac loss of high-temperature superconductor (HTS) coils at frequencies between 50 and 200 Hz, and in applied ac fields of up to 0.04 T. The mass boil-off calorimeter incorporated a glass cryostat, a copper field coil, and two mass flow meters. The response of the gas flow to a step change in the applied magnetic field was found to have a time constant of about 600 s. Under suitable experimental conditions, it was possible to measure the ac losses of coils with an accuracy of ±0.3 W. The ac loss characteristics of an HTS pancake and two HTS solenoid coils are presented and the accuracy of mass flow calorimetry in liquid nitrogen is reported on.