Transient Behavior of a REBCO No-Insulation or Metal-as-Insulation Multi-Pancake Coil Using a Partial Element Equivalent Circuit Model

Abstract

REBCO No or Metal Insulation magnets open the way for very high field magnets but their transient operation must be understood and optimized. We present then the thermo-electric behavior of an HTS pancake with different values of the radial contact resistance. The model is built from a Partial Element Equivalent Circuit (PEEC) model coupled with a 2D finite difference thermal model and with a 3D magnetic model. We consider different transient cases from the simple driven charge-discharge to the local quench inside a pancake. Then we extend the model to a magnet made of several pancakes powered in series and we observe the temperature distributions, the radial and azimuthal current of each sector of the pancakes due to a source term generated on one sector in one of the pancakes. This model makes possible to investigate the influence and optimize the turn-to-turn resistance. With low contact resistance, the current flows radially from one turn to another, bypassing the local defect, but the charging time increases. With high contact resistance, the current flows through the resistive zone, causing a local thermal overheating, but the magnet charging time is reduced. A compromise must be found.