  Rare-earth (Re)Ba2Cu3O7-x (ReBCO) no-insulation (NI) coil is widely concerned
due to its excellent electromagnetic and thermal properties. However, the
presence of the turn-to-turn shunts in NI coils leads to that complexity of
numerical simulation is increased. In this paper, a modified J model is
proposed and the corresponding explicit-implicit hybrid algorithm is designed
to calculate NI coils. The numerical results are in good agreement with the
experimental data and the circuit model. The homogenization model is also
proposed to simulate the large-scale NI coils in the background magnets. The
modified J model has good accuracy and fast calculation speed, which can also
be used to solve electromagnetic fields of insulation coils efficiently.
