Sabbagh and Park Visit KSTAR Superconducting Tokamak Facility in South Korea

Steve Sabbagh (APAM alumn, Adjunct Professor and Senior Research Scientist) and Young-Seok Park (APAM Associate Research Scientist) recently visited the National Fusion Research Institute (NFRI) in Daejeon, South Korea to conduct an experiment on the KSTAR superconducting magnetic fusion tokamak device attempting to demonstrate plasma operation at high ratios of plasma pressure to magnetic field and plasma current (normalized beta) and to extend the understanding of plasma rotation control in the device. The machine was successfully operated at reduced toroidal field as low at 0.9T and record values of normalized beta for the device exceeding 4.3 were produced transiently over a range of plasma internal inductance from 0.65 – 0.85 as computed using full KSTAR equilibrium reconstructions. The maximum normalized beta exceeds by 50% the theoretical global MHD mode ideal no-wall beta limit, and is more than 85% of the design value for the device. These experimental plasmas may be limited in performance by global plasma instabilities. These experiments are a proof-of-principle for the existence of this high normalized beta operational regime in KSTAR, and further experiments will attempt to maintain these plasmas for the maximum duration allowed by the device (presently several tens of seconds). Initial examination of the expanded rotation control experiments confirm the favorable lack of hysteresis previously found as the applied 3D braking field magnitude is changed. (S.A. Sabbagh)