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 re sult of the microstructural observation, accumulated radiation damage (disl ocation loops) due to charge exchange (CX) neutrals were observed only in t he specimens pointing to the lower half of plasma and almost no damage in t he specimens pointing to the upper side. These results indicate that the lo wer 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-e nergy ions trapped in a toroidal ripple. The mean flux was estimated to 4.2 x 10(17) particles m(-2) s(-1) sr(-1) from the lower side by using the are al density (A.D.) of dislocation loops. The depth distribution of the dislo cation loops shows a significant contribution of the high-energy CX neutral s. The energetic CX neutrals will give a great impact on material degradati ons. (C) 2001 Elsevier Science B.V. All rights reserved.