The experiments have showed that the actual value of magnetic field in the magnet wound by rare-earth (RE) Ba2Cu3O7−x (REBCO) tape during the operation is less than its design value due to the effect of screening current-induced magnetic field (SCMF). Some simulation methods have been used to calculate the SCMF. In this paper, a modified model is proposed to estimate the SCMF of the magnet based on the previous simple model. The inductance correction and field-dependent critical current density are considered in the modified model. Thereinto, two parameters, named reversal coefficient and Nagaoka coefficient, are introduced in the model. The former is used to track the location of the minimum SCMF value in the charging process, and the latter is applied to correct the induction of the magnet. The numerical results indicate that the SCMF estimated by the modified model is in agreement with those from experiments and finite element method (FEM). Moreover, the effects of electromagnetic and geometrical parameters on the reversal coefficient and Nagaoka coefficient are also investigated. Finally, the model is extended to estimate the SCMF of no-insulation (NI) magnet.

The increase in contact resistance of no-insulation (NI) high-temperature superconducting (HTS) coil was observed in the high-field test, which may be related to the mechanical deformation and the separation between adjacent turns in the coil. The large electromagnetic force generated in the high magnetic field can cause the separation between adjacent turns of the NI coil, which can affect the contact resistance of the magnet. An electromagnetic-mechanical model is built to study the effect of separation on the contact resistance and field delay time of an NI layer-wound coil. The numerical results show that the large electromagnetic force generated in the high field leads to the local separation between adjacent turns and the increase of contact resistance of the NI layer-wound coil. Moreover, a higher external field or target current can result in a larger area of separation region, a higher contact resistance and a shorter characteristic field delay time. The overband can restraint the mechanical deformation and separation between turns of the NI coil in the high field, which suppresses the increase of turn-to-turn contact resistance.