Evaluation for boron mixed graphite and high Z metal as plasma facing material

The boron doped or mixed graphite was evaluated as a plasma facing material in terms of erosion due to hydrogen ions, and evaporation of boron and boron oxide, based on our experimental data obtained so far. The evaporation of boron and boron oxide became dominant when the temperature exceeded 900 and 1000deg C, respectively. The reduction of the radiation enhanced sublimation due to hydrogen ions was not clearly by the boron doping or mixing. The possibility to use a high Z metal such as W as the divertor plate was analytically evaluated. For the high Z impurity concentration to be less than the allowable level for an ignition, the conditions required for the divertor plasma density and the divertor geometry were examined. In addition, the effect of the contamination of the main chamber wall due to high Z impurities is discussed. For both the boron mixed graphite and the high Z metal to be effectively used as the divertor plate in the next device, it is suggested to largely expand the divertor configuration. (orig.)