Studies of tungsten erosion at the inner and outer main chamber wall of the ASDEX Upgrade tokamak

A critical issue for the choice of main chamber first wall materials in fut ure fusion devices such as ITER is the erosion rate due to bombardment by c harge-exchange (CX) neutrals. Due to the relatively small flux density of i mpacting particles, respective measurements are only possible using long te rm samples (LTS) exposed for a full experimental campaign. In ASDEX Upgrade , CX erosion has been studied extensively for tungsten on the inner heat sh ield by placing four W coated tiles at different poloidal positions in one toroidal sector. During the same campaign, several LTS were placed at diffe rent poloidal and toroidal positions of the outer wall. C-13 and Cu coated graphite probes were also used in order to test and compare W low and mediu m Z alternatives. The erosion results from the probes are compared with the calculated erosion CW. Eckstein, C. Garcia-Rosales, J. Roth, W. Ottenberge r IPP Report, IPP 9/82]; [H. Verbeek, J. Stober, D. Coster, W. Eckstein, R. Schneider Nucl, Fus. 38 (1998) 12] and a figure of merit (F, of M.) betwee n several materials is proposed which also takes into account the plasma is otope effect in CX erosion. (C) 2001 Elsevier Science B.V. All rights reser ved.