A Novel Calorimetric Method for Measurement of AC Losses of HTS Tapes by Optical Fiber Bragg Grating

This paper presents an innovative calorimetric method for measurements of ac losses of high-temperature superconducting (HTS) tapes by using the effect of optical fiber Bragg grating (FBG) wavelength shift resulting from temperature change caused by ac losses, where it is adopted as a temperature sensor. The HTS specimen on which the FBG is attached on are adiabatically processed before measuring. Compared with conventional electric and calorimetric methods, FBG temperature sensor has the advantage of rapid response and anti-electromagnetic interference due to its thin geometrical sizes and optical characteristics; it is thus very suitable to ac loss measurement of HTS applications in much more complicated electromagnetic circumstance. By measuring the effect of temperature on wavelength shift in low temperature range, it is indicated that FBG has good-enough repeatability of dependence of wavelength shift on temperature measurement around liquid nitrogen temperature of 77 K. After calibration, ac loss of BSCCO HTS tape in self-field is measured by the FBG sensor, and the measured loss is also measured by conventional electric method using a lock-in amplifier. It is shown that the measured ac loss is in agreement with the results measured by electric method and those based on Norris theory so that the presented calorimetric method is available for measuring the ac loss of superconductors and expected to be generalized to ac loss or thermal measurements of other bulk superconductors.