Nitrogen boil-off method of measuring AC losses in YBCO coils

The nitrogen boil-off method, which is categorized as one of the calorimetric methods, has been developed as a practical method for measuring AC losses in high temperature superconducting (HTS) coils. The boil-off method offers direct and convenient measurement compared to the electric method. The measurement sensitivity of about 0.5 W was confirmed by the improvement of sample vessel structure and the control of the heater power. This paper reports the results of a comparison of the AC losses in superconducting coils using YBCO tapes measured with the boil-off method and those obtained by the electric method and by analysis.