Study of Calorimetric Self-Field AC Loss Measurement of HTS Stacks Using FBG Sensors

AC loss plays an important role in the design of the device employing HTS magnet. Therefore, it is important to measure the AC loss in HTS magnet. In this work, we studied the calorimetric self-field AC loss measurement of a four-tape HTS stacks using Fiber Bragg Grating (FBG) sensors. Three cryogenic FBG temperature sensors with different coating and installation were selected for the AC loss measurement. The calibration between power loss and wavelength shift was carried out by a resistance heater before the AC loss measurement. With the calibrated FBG sensors, the AC loss measurement was measured at 67 Hz and 89 Hz. These measurements were carried out at 77 K through conduction cooling by sealing the sample in a thermal insulator. The measured loss results were verified through comparison with the Norris models as well as the electrical measurements of AC loss. Finally, the magnetic strain effect on loss measurement was evaluated experimentally. The results in our paper shows that the calorimetric method based on the proposed FBG sensor can be used for the AC loss measurement of a four-tape HTS stack, and the magnetic strain of a four-tape stack has no effect on the AC loss measurement, which provides the possibility of using FBG sensors for ac loss measurement on HTS stacks.