Quench Analysis of a Multiwidth No-Insulation 7-T 78-mm REBCO Magnet

Due to the self-protecting feature, no-insulation (NI) high-temperature superconductor magnets have been regarded as a reliable option to generate high fields, yet their intrinsic charging delay still remains a major drawback. To apply the NI technique for actual high-field user magnets, however, postquench transient behavior of such magnets need to be fully understood, particularly the electromagnetic interaction among magnetically coupled subcoils. Recent publications have shown successful simulations of the transient behavior of a single NI coil or a multicoil magnet using distributed network models. Even though these approaches are very accurate, they often require substantial computation time, especially when multiple iterations are required during design or analysis of an NI magnet having a large number of coils. This paper presents a simple circuit approach that may be effective for quench simulation of multicoil NI magnets. Each NI subcoil in a magnet is lumped into a single inductor with a resistor in series and a resistor in parallel. This approach has allowed us to simulate the whole magnet system within reasonable time without compromising the understanding of mutual interactions of all of the subcoils after quench, namely change in parameters such as voltage, current, and temperature with respect to time and coil to coil normal zone propagation in an electromagnetic manner. We verified the proposed approach by analyzing the quench process in a previously built 7 T, 78 mm all-REBCO NI magnet (by MIT), and by doing the first ever comparison between the simulated results with the data measured from actual experiment.