Study for reducing the screening current-induced field in a 10-MHz no-insulation magnet using current sweep reversal method

This paper reports the effects of the current sweep reversal (CSR) method on the screening current-induced field (SCF) in a no-insulation (NI) magnet wound with high-T_c superconducting (HTS) coated conductor (CC), as determined experimentally and analytically. To quantify the SCF in the NI magnet, the magnetic flux density (B_z) was calculated using the equivalent circuit model and compared to the B_z obtained empirically. In addition, the charging scenario for the current sweep reversal (CSR) method was modified to eliminate the effect of the charging delay observed in NI magnets on the SCF. The SCF observed for the NI magnet charged directly at 30 A was markedly reduced when the magnet was subjected to the modified charging scenario for CSR at 36 A by decreasing the "hysteresis of the SCF" to zero base line. The results demonstrated the validity of the proposed approach for the enhancement of the temporal stability and spatial homogeneity of NI-NMR magnets via SCF reduction.