Design and AC Loss Study of a High-Temperature Superconducting CS Model Magnet for Fusion Applications

In an effort to thoroughly investigate the manufacturing processes of central solenoid (CS) magnets for Tokamak devices, this study has designed and constructed a CS model magnet. The magnet is wound with a double-tape soldered conductor (DTC) and stainless steel tape, consisting of two double-pancake (DP) coils with 30 x 2 turns each. By optimizing the winding, joint, and insulation techniques, the magnet achieved a critical current of 269 A at 77 K. The inductance of the magnet is 9.4 mH. When the magnet is applied to a direct current (DC) with an amplitude of 200 A, the central magnetic field is 0.07 T. Given that alternating current (AC) loss is a significant issue in the design of CS magnets, leading to higher cooling costs, increased operational risks, and possible irreversible damage to superconducting devices, this paper primarily focuses on studying AC loss in the designed CS model magnet. Simulations were performed using the H-formulation, J-formulation, and T-A formulation models, and the AC loss of the magnet was experimentally measured using the electrical method. The experimental results revealed that the AC loss for the CS model magnet was 5.1 J. Among the simulation models, the H-formulation model provided results closest to the actual values, with a significant increase in computational efficiency achieved by employing a homogenized method. This paper conducts a detailed comparative analysis of the characteristics and applicability of these three simulation models and investigates the effects of the AC cycle, current amplitude, and charging rate on AC loss through experimental studies. Ultimately, we designed and applied a current to the CS model magnet that matched the charging rate in the CS magnet within the tokamak device and found that the AC loss was the greatest during the plasma breakdown process.