The Design and Fabrication of an Insulated Multi-Tape Parallel-Wound REBCO Superconducting Coil

Abstract This study demonstrates the design, fabrication, and experimental validation of an insulated multi-tape parallel-wound REBCO superconducting coil for compact Spherical Tokamaks (STs). The coil meets the demanding requirements of high engineering current density and a constrained bending radius (inner diameter: 171.7 mm) through an innovative winding technique. This method co-winds 12 triple-stacked REBCO conductors (equivalent to 36 tapes per turn) with reliable turn-to-turn insulation, along with inter-pancake transposition to minimize AC losses. A reduced scale test coil, consisting of two double pancakes (56 turns in total), was fabricated and tested. Pre-impregnation performance at 77 K under self-field conditions yielded a critical current (Ic) of 1395 A, a central magnetic field of 243 mT, and an inductance of 1.96 mH, all within 5.6% deviation from simulated values. After vacuum pressure impregnation (VPI), the Ic of the coil degraded less than 5%. Simultaneous quench across all 12 conductors confirmed effective current sharing enabled by transposed joints and inter-conductor insulation. This work offers valuable experimental support and technical approach for the engineering design of central solenoid magnets in future large-scale fusion devices.