APPLICATION OF 4C CODE TO THE THERMAL HYDRAULIC ANALYSIS OF AC LOSSES IN THE KSTAR PF SUPERCONDUCTING COILS

Korea Superconducting Tokamak Advanced Research (KSTAR) began operation in 2008 and is a fully superconducting tokamak using ITER-like superconductor. All of the SC coils, using cable-in-conduit conductors (CICCs), are cooled with forced-flow supercritical helium (SHe) at 4.5 K and 5.5 bar, to maintain a superconducting state. We consider here the central couple of the PF coils, which during operation is subjected to sharp current transients, which induce AC losses in the superconducting coils due to the change in magnetic field, which leads to the backflow of the helium. The thermal hydraulics due to one of the trapezoidal current pulse in the PF1L coil is analyzed, with ramp up rate of 1 kA/s and ramp down rate of 10 kA/s, with maximum current of 10 kA, using the recently developed 4C code. The main thermal-hydraulic characteristics (evolution of temperatures, pressures, mass flow rates) at different coil locations are computed and compared with the measurements, showing that expected AC losses turns out to be much smaller that the experimental ones.