Numerical investigation of screening current effects and mitigation strategies in REBCO accelerator bending magnets
Abstract
High-temperature superconducting (HTS) coated conductors have attracted increasing attention for high-field accelerator applications owing to their superior electromagnetic performance under strong magnetic fields. However, the pronounced screening-current effect can induce magnetic-field errors and temporal field drift, posing a major challenge. Although overshoot excitation and vortex shaking driven by applied alternating-current magnetic fields have been recognized as effective approaches for suppressing screening currents, quantitative studies of their suppression behaviour are still lacking. In this paper, a REBCO HTS dipole magnet designed for the Hefei Advanced Light Facility is investigated using a multiphysics framework that combines a multi-group no-insulation circuit with an extended H-formulation electromagnetic model and a thermal model. The effects of current ramp rate, overshoot amplitude and holding time, and shaking-field amplitude, duration, and frequency are evaluated. Faster charging generally increases the post-excitation screening-current-induced field (SCIF), power loss, and temperature rise. Overshoot excitation provides limited and non-monotonic suppression within the thermally stable range, whereas vortex-shaking excitation produces greater residual suppression through repeated field reversals that reconstruct the inherited screening-current distribution. For representative thermally stable cases, a 285 A overshoot reduces the magnitude of the aperture-centre SCIF from 20.9 to 15.3 mT, while a 400 mT, 1 Hz shaking field applied for 60 s reduces it to 6.8 mT. Stronger or prolonged shaking also increases heat accumulation, resulting in suppression saturation or deterioration and possible thermal instability. These results provide an electromagnetic–thermal interpretation of screening-current mitigation and guidance for selecting excitation parameters in HTS accelerator magnets.