Wall-conditioning plasmas by ECRF heating in KSTAR

Wall-conditioning plasmas by ECRF heating (ECWC plasmas) were investigated in KSTAR's experimental campaigns of 2010 and 2011. Pulses of 110 GHz ECH with an RF power of 200-300 kW were injected into the vacuum vessel, which was filled with helium at a gas pressure similar to 1 x 10 (3) mbar. In 2010, the second harmonic of ECH was applied and it was found that the ECRF wave normal to the toroidal field was essentially important for producing high-density plasmas and the uniformity of the plasma was significantly changed with an additional poloidal field pattern by B-H and B-V. In 2011, the fundamental ECH was applied with additional B-H = 0.02 T. The ECWC plasma extended radially toward both the high toroidal field side and low field side. The post-disruption first wall was successfully recovered by 20 pulses of the ECWC plasmas, equivalent to ECWC for 7 min. (C) 2013 Elsevier B. V. All rights reserved.