First comprehensive particle balance study in KSTAR with a full graphite first wall and diverted plasmas

Abstract

The first comprehensive particle balance study is carried out in the KSTAR 2010 campaign with a full graphite first wall and diverted plasmas. The dominant retention is observed during the gas puffing into the plasmas. Statistical analysis shows that deuterium retention is increased with the number of injected particles. Particle balance analysis in the whole campaign shows that the long-term retention ratio is similar to 21%, and the retention via implantation can be partially recovered by He-glow discharge cleaning (GDC), while long-term retention via co-deposition. The wall pumping capability is decreased with the D-2 plasma due to fuel accumulation in the first wall, and He-GDC is effective in recovering the wall pumping. Boronization assisted by the D-2 glow discharge using C2B10H12 strongly enhances the wall puffing and leads to negative retentions, but the wall pumping capability is recovered in 2-3 days by He-GDCs. Electron cyclotron resonance heating enhances wall outgassing during the discharge. During a diverted H-mode discharge, the retention rate decreases to a very low value, and a high divertor particle flux of similar to 1.5 x 10(23) D s(-1) is observed indicating the strong recycling divertor. The amount of recovered deuterium after discharges mainly depends on the plasma-wall interaction when the plasma is terminated, and disruptive discharges release more particles from the first wall.