Erosion and deposition processes in tokamaks

Erosion of limiters, walls and divertor plates is likely to be a serious concern in the next generation of fusion devices. The main mechnisms of erosion are reviewed and the spatial distribution of erosion and deposition are discussed. measurements of erosion and redeposition have been made at the JET limiters under different conditions and net erosion in the range 10-100 micrometer detected after typically 3000 10 s discharges. Modelling of the distribution is in quite good agreement with the experimental data and net to gross erosion ratios of 0.2 to 0.3 are calculated. The problem of extrapolating to reactor conditions is discussed. While there are serious difficulties in carrying out this extrapolation, the higher edge densities envisaged should lead to lower ratios of net to gross erosion than in present experiments. (author). 46 refs.; 14 figs.; 2 tabs