Screening-current-induced mechanical damage and critical current degradation in epoxy-impregnated REBCO insert coils

Abstract

Abstract In recent years, there has been growing concern about the mechanical deformation induced by the screening currents in high-field high-temperature superconducting (HTS) magnets. Screening-current-induced mechanical damage and critical current degradation have emerged as significant issues in the design and operation of HTS magnets. Currently, it is a challenging topic to consider both the nonlinear E–J power-law relationship of the REBa2Cu3O7−x (REBCO) coated conductors (CCs) and the nonlinear interface-damaged constitutive relationship in the numerical simulation. This paper presents an electro-mechanical model combining T–A formulation with the cohesive zone model for an epoxy-impregnated REBCO insert coil, taking into account the mechanical damage dependence of the critical current of REBCO CCs. The model is validated with experimental data. Additionally, numerical results indicate that delamination and current-carrying degradation in the coil are caused by the large electromagnetic force generated by the screening current during the high-field magnetization process. The effects of screening currents on the electromagnetic and mechanical properties of the coils exhibit a significant difference between scenarios with and without consideration of the damage-dependent critical current of REBCO CCs. The underlying mechanisms leading to edge and internal damage of the REBCO CC in the coil are clarified by different failure modes. Simulations neglecting the degradation of the critical current can overestimate the stress, strain, and damage zone growth of the coil, while underestimating the current-carrying deterioration in the high field. Furthermore, a detailed analysis is conducted on the screening-current-induced mechanical damage and critical current degradation under different background fields. Finally, the influences of the structural parameters, bobbin, overband and geometric position on the delamination damage and current-carrying degradation of the coil are further investigated. This work could provide theoretical references for the design and analysis of high-field HTS insert magnets.