Impurity deposition and retention of discharge gas on plasma facing wall in LHD

Abstract

Several material probes of SS 316L and graphite were placed on the plasma facing walls of Large Helical Device (LHD) along poloidal and toroidal directions during 4th experimental campaign, in order to investigate the plasma surface interactions and the wall conditions. The retained amount of helium was large in the probes located near the plasma, while, that of hydrogen was large far from the plasma. The retained amounts of discharge gases, impurity gases and the deposition of iron were large near the glow discharge anodes.