Anisotropic radiation damage by charge exchange neutrals under tokamak discharges in TRIAM-1M

Thin foil specimens were exposed to tokamak discharges in TRIAM-1M. As a result of the microstructural observation, accumulated radiation damage (dislocation loops) due to charge exchange (CX) neutrals were observed only in the specimens pointing to the lower half of plasma and almost no damage in the specimens pointing to the upper side. These results indicate that the lower half of the plasma is the major source for energetic CX neutrals. This anisotropy can be explained by the effect of the gradient B drift of high-energy ions trapped in a toroidal ripple. The mean flux was estimated to 4.2×1017 particles m−2 s−1 sr−1 from the lower side by using the areal density (A.D.) of dislocation loops. The depth distribution of the dislocation loops shows a significant contribution of the high-energy CX neutrals. The energetic CX neutrals will give a great impact on material degradations.