Generation and removal of light impurities in TPE-2 plasma

Impurity generation from the wall of alumina ceramic discharge tube precoated with titanium and cleanning of the wall are described. The clean wall was accomplished whose dominant light impurity is the carbon and the concentration is about 1018/m3, by operating more than 104 shots of cleanning discharge and main screw pinch discharge. The plasma overcome the radiation barrier. Under the pressure higher than 8 m Torr, the oxygen line spectrum and radiation loss power increase simultaneously. The temperature of the plasma seems to be limited due to oxygen radiation loss in this pressure region. The screw pinch plasma is free from impurity, as far as the direction of the pointing vector is always kept inward. (author)