Simulation of self-arresting screening current stress damage in a >900 MPa REBCO coil using detailed conductor models

Abstract

Abstract

Abstract Screening current in REBCO-coated conductors amplifies the Lorentz force. In high fields, screening current stress (SCS) can cause excessive magnetic stress and subsequent plastic deformation of the conductor. This is recognized as a key issue in the high-field, high-stress REBCO magnet technology at present, since such plastic damage degrades local superconductivity and eventually affects the coil performance. Although the importance of SCS has been widely recognized and extensively investigated, relevant studies are mostly limited to the calculation of peak stress and strain, rarely focusing on the damage initiation and propagation mechanism. Additionally, simulation studies of REBCO coils consider key conductor properties by referring to measured results in the literature, but rarely employ measurements obtained from the conductor used in the tested coil. We therefore performed an integrated conductor-to-coil study. First, we selected one of our previous high-field REBCO coil experiments, where the coil did not experience quench damage, although SCS-initiated wavy plastic damage and subsequent coil performance degradation were observed during the test. The conductor used in the coil was parameterized and formulated in detail based on measured electromagnetic and mechanical properties. Then, simulation work was performed to investigate plastic damage initiation and propagation, demonstrating that SCS caused local plastic damage, degrading local J c and reducing global I c , changing the effective current path, and shifting the electric field center towards the undamaged region from the physical center. One key finding is that plastic damage propagation becomes self-arresting and remains confined to a limited region of the conductor width because local J c degradation redistributes the screening current and consequently alters the stress distribution. This paper presents a detailed conductor model and SCS simulations and discusses their agreement with experimental observations.