Analysis of AC Losses in KSTAR Superconducting PF Magnets at Low Current Ramp Rates

To achieve nuclear fusion energy generation, continuous confinement of high-current and long-pulse plasma is necessary. KSTAR has been conducting experiments to achieve this goal. In order to maintain a steady state of plasma current, the superconducting magnets of the tokamak should also be operated stably, with heat controlled to a minimum. However, a slight increase in the outlet temperature of the KSTAR PF (poloidal field) magnet and current ripple were observed, particularly when the current ramp rate is 0.5 kA/s or less. In this range, the evaluated AC loss showed a different trend compared to the range where the current ramp rate was higher than 0.5 kA/s. The total heat load was observed to be significantly higher than the theoretical value, which means that losses must be added. This could be a hindering factor in the operation of long pulse plasmas. To ensure stable plasma control, the current operation of the superconducting magnet coils should be optimized and the AC losses should be applied accurately in the full range of ramp rate. In this article, the parametric study of AC losses based on the results of the PF coil in the low current ramp rate were analyzed to stably operate the superconducting magnet.