Investigation on modification of plasma facing surface under long duration discharges by means of a collector probe in TRIAM-1M

Metallic specimens mounted on a collector probe head were inserted in the scrape-off layer and exposed to long pulse tokamak plasma in TRIAM-1M. Strong radiation damage (formation of interstitial loops) was caused by high energy (>2 keV) charge-exchange hydrogen neutrals. The surfaces of the probe specimens were covered by new material made of co-deposited in-vessel elements such as Fe, Cr, Mo, O and C. The deposited layer was often exfoliated by blistering. These results indicate that energetic hydrogen neutrals and the co-deposition of impurities considerably change the surface properties of plasma facing components and even introduce new impurity sources.