Interleaved Transposition Winding: An Innovative Approach for Inductive Balancing in High-Temperature Superconducting Non-Twisted Stacked Cable Coils for Central Solenoids

Abstract The high-temperature superconducting (HTS) Central Solenoid (CS) coil in Spherical Tokamaks (STs) drives the plasma current by carrying rapidly varying currents, ultimately confronting the critical challenge of severe AC losses. To reduce AC losses, an interleaved transposition winding method based on a special joint for inductive balancing is proposed. This study develops a multi-physics framework integrating an equivalent circuit model, T-A formulation, and thermal analysis. This framework is applied to study a 1/10-scale central solenoid (CS) model coil co-wound with 36 HTS tapes, which attains a peak field-on-coil of 13.3 T at 7.2 kA terminal current and a maximum magnetic ramp rate of 70 T/s, thereby validating the proposed winding methodology. Numerical results demonstrate a tenfold reduction in hysteresis losses via the novel winding strategy, while the coil's peak temperature remains below 54 K post-discharge. This method enables non-twisted stacked HTS coils to achieve both fabrication simplicity and AC losses suppression, advancing compact fusion magnet design.