Erosion of beryllium under high-flux plasma impact

Abstract

Be sputtering yields, measured by weight loss, in PISCES-B are a factor of 5–10 less than that predicted by binary collision approximations. Measurements show the BeO surface is removed early in the plasma bombardment. Modeling of molecular ions (D2+ and D3+) species and redeposition cannot explain the difference. Surface morphology that evolves during the exposure reduces the sputtering yield by a factor of 2–3. Plasma fuel atoms retained in the surface decrease the sputtering yield compared to calculations of a pure Be surface. These effects may explain the measured erosion rates in the absence of Be impurities within the plasma. By introducing Be impurity ions into the plasma, it is possible to simulate a controllable amount of redeposition. The weight loss from eroding Be targets, with Be seeding, is unchanged until the concentration of Be ions in the plasma greatly exceeds the sputtering yield in the non-beryllium seeded exposure.