Study on AC loss and temperature rise characteristics of HTS bulk with a fillet defect under applied alternating magnetic fields

The high temperature superconducting (HTS) bulk needs to work in a LN 2 environment for a long time. Under the action of applied alternating magnetic field, the flux movement in the HTS bulk induces the AC loss in the HTS system, which leads to the temperature rise effect in the HTS bulk, and will affect the stability of the HTS system. A majority of previous research focused on ideal superconducting bulks, and few researches have been done on the AC loss and temperature rise characteristics of superconductors with defects. In this paper, a non-ideal HTS bulk with a fillet defect is considered, and the two-dimensional partial differential equation is established based on the H-formation. A coupled electric-magnetic-thermal multi-field of the non-ideal HTS system is analyzed employing the PDE module and heat transfer one of the finite element software COMSOL. The temperature distribution and the AC loss of the non-ideal HTS bulk under alternating magnetic fields are investigated. The results show that the fillet defect causes the temperature distribution in the HTS bulk to change from bimodal to unimodal. The maximum temperature of the non-ideal HTS bulk decreases as a quadratic polynomial function with the increase of defect content, and the AC loss of HTS decreases linearly. The maximum temperature in the non-ideal HTS bulk increases linearly with the amplitude increasing of the applied magnetic field. A transition value of the applied magnetic field amplitude is found at which the relation between the AC loss and the magnetic field amplitude changes. The mechanism of redistribution of trapped magnetic field, temperature and shielding current induced by HTS bulk defects is obtained in this paper, which will have significance for industrial application of HTS system.