Physics and Experimental Results of KSTAR ECH

Since the first plasma in Korea Superconducting Tokamak Advanced Research (KSTAR), the electron cyclotron heating (ECH) system has been an essential tool for ECH-assisted start-up using second-harmonic 84-GHz and 110-GHz ECH and for experimental studies of other physics issues such as edge-localized mode control, rotation control, sawtooth control, tearing mode control, and core impurity control for long-pulse discharge and noninductive start-up. The loop voltage in KSTAR is limited by superconducting ohmic coils and a thick vacuum vessel. The ECH-assisted start-up was useful to overcome burn-through during the ramp-up phase with limited loop voltage by the electron cyclotron beam injection before or after the onset of the inductive loop voltage to reduce resistive power consumption. Later, the 170-GHz ECH system is installed as a main electron heating and local current drive for the control of magnetohydrodynamic modes such as sawteeth and neoclassical tearing modes. The 170-GHz gyrotron is an ITER preprototype gyrotron developed by the Japan Atomic Energy Agency. Second-harmonic 170-GHz ECH-assisted start-up was also attempted with a raised toroidal magnetic field of 3 T in the 2011 KSTAR campaign, and flux saving in the ramp-up phase was observed. This lecture describes the physics issues and experimental results of the KSTAR ECH system. The present status and an upgrade plan of the KSTAR ECH system is also described.