EROSION AND IMPURITY PRODUCTION OF C AND BE - A COMPARISON

One of the many criteria for the use of carbon and beryllium as first wall materials in plasma machines is erosion under particle bombardment. The sputtering yield of carbon, while being smaller than that of Be at room temperature, shows a strong dependence on temperature. The chemical reaction of carbon with energetic hydrogen ions leads to a maximum around 900 K. Above 1200 K radiation enhanced sublimation increases the sputtering yield independent of ion species. Both these enhanced sputtering yields leads to the release of thermal particles, decrease with increasing ion flux and may be strongly influenced by impurities on the carbon surface. The shielding efficiency of the plasma boundary for the sputtered particles is dependent on their velocity and ionization energy. The existing data on sputtering are discussed in respect to the different applications in fusion machines of both materials.