Determination of best operation parameters of electron cyclotron wall conditioning in KSTAR

Abstract

Dependence of EC injection power (0.6 and 1.4 MW), EC injection width (0.1–1.0 s) and prefilled He pressure ( 2 . 8 × 1 0 − 5 ∼ 2 . 2 × 1 0 − 3 mbar) on D 2 outgas efficiency is investigated at a toroidal field of 2.4 T in a poloidal trapped particle configuration with an EC wave frequency of 140 GHz (X-mode) and a second harmonic resonance layer near the machine center (1.73 m). With increasing EC injection power, D 2 outgas increases clearly. The dependence of the EC power injection is the most pronounced between the scanned parameters. It is found that an optimum prefilled He pressure for D 2 outgas exists under the condition of a constant EC injection power. It is observed that both high EC injection power and the optimum prefilled He pressure enhance the ion flux to the center stack, suggesting that the D 2 outgas originates from the center stack. • Parameter scan (prefilled He pressure, EC pulse width, EC power) was performed to determine best ECWC parameters in KSTAR. Within this experiment. • In terms of D 2 removal efficiency, optimum He pressure existed, higher EC injection power was better but EC injection length was less effective. • It was suggested that D 2 outgassing originated from the center stack. • The reason why ECWC at highest He pressure with very small D 2 outgassing resulted in successful burn-through was still unclear.