Physics Design of Poloidal Field, Toroidal Field, and External Magnetic Diagnostics in KSTAR

The Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak will have superconducting magnets for both the poloidal field (PF) coils and the toroidal field (TF) coils. The physical arrangement of the PF configuration has 14 coils external to the TF coils. The analysis of the equilibrium flexibility of the KSTAR PF system determines the coil currents required to maintain prescribed equilibrium configurations over the desired range of operational parameters specified for I_p (q₉₅), _N, and l_i(3). Constraints on the plasma separatrix and the flux linkage through the geometric center of the plasma are specified for the free-boundary equilibrium calculations. The ripple magnitude due to the finite number of TF coils and the size of the port for the neutral beam (NB) injector determine the number, size, and shape of TF coils. Two ripple criteria for a shaped plasma are used for types of ripple transport. The current design of the TF coil, with 16 coils and a D shape, is big enough to satisfy requirements for the ripple magnitude at the plasma and to provide adequate access for tangential NB injection. The external magnetic diagnostics, magnetic probes and flux loops to detect the plasma boundary are designed by the EFIT code, which uses a realistic distributed current source constrained by equilibrium. The proposed configuration with 52 full toroidal flux loops and 78 magnetic probes results in <0.7 cm deviation at critical points, with the Gaussian-distributed 3% random root-mean-square perturbation in the signal.