First-wall erosion in fusion reactors

The subject of sputtering by ions and neutrons has been reviewed, and yields for various ions on Nb in the energy range of 100 eV to 100 keV have been assembled. Furthermore, evaporation rates of Nb for stationary conditions and for short time energy pulses are calculated, and a brief summary is given of the blistering phenomena. For a Tokamak or Stellarator-type CTR first-wall bombardment is estimated from the a-energy released in the plasma. First-wall-erosion data as well as the flux of sputtered and evaporated Nb-atoms back to the plasma are calculated for two CTR reactors with a difference of a factor of 10 in first-wall load. It is shown that sputtering can account for wall deterioration at a rate of more than 1 mm per year.