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 110GHz ECH with an RF power of 200–300kW were injected into the vacuum vessel, which was filled with helium at a gas pressure ∼1×10−3mbar. 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 BH and BV. In 2011, the fundamental ECH was applied with additional BH=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 20pulses of the ECWC plasmas, equivalent to ECWC for 7min.