A method to monitor the current in a high temperature superconductor tape at cryogenic environment

In this work, the performance of a Fiber Bragg Grating (FBG) sensor attached on a cryogenic compatible giant magnetostrictive material (GMM) to monitor the current in a Yttrium barium copper oxide (YBCO) high temperature superconductor (HTS) is reported. The sensors were installed in vertical, horizontal, standing and angled configurations on an HTS tape. The current flowing in an HTS tape generates a self magnetic field around the tape and its magnitude depends upon the applied current. The self generated magnetic field induces a corresponding strain in the GMM material attached to the FBG sensor, which in turn change the Bragg wavelength. The sensor installed in horizontal and standing configuration shows no change for applied current, whereas the total Bragg wavelength shift of the vertical and angled configuration has been found to be 124.75 pm and 87.5 pm respectively. The average sensor sensitivity of vertical configuration has been estimated to be 0.39 pm / A and for angled configuration, it was found to be 0.27 pm/A. Also, sensor resolution together with measurement unit was found to be 2.56 A for vertical and 3.70 A for angled configuration. In this paper, the design and technology requirements to adapt the FBG sensor concept for current monitoring in an HTS conductor is presented. Initial experiments, which demonstrate the current measurement at 77 K is reported.