A Simple and Versatile Evaluation Method of Thermal Stability of NI HTS Magnets

In this article, a simple and versatile method of thermal stability evaluation for no-insulation (NI) high-temperature superconducting (HTS) magnets is proposed. Thermal stability is fundamental to superconducting magnets. The evaluation of coil temperature is an essential part of magnet design even though NI HTS magnets exhibit high thermal stability. Already proposed methods with complicated equivalent circuits, such as a partial element equivalent circuit (PEEC) model and a network model, require a long computation time and complication in coding. Hence, a simple way to evaluate the thermal stability of NI HTS coils is strongly desired; e.g., for a preliminary-design purpose. A method proposed in the article is a simple analytical formula derived from an equivalent RL-parallel circuit model of an NI HTS coil. The formulation considers a cooling effect with a simple assumption and Joule heating on radial (turn-to-turn contact) resistances. For a trial of the proposed simple evaluation, the thermal stability investigation is presented comparing the temperatures of the sudden discharge and ramp down. The results of the proposed analytical method are also compared with the PEEC model.