Impact of surface morphology on sputtering during high-fluence plasma exposure

The erosion behavior of beryllium targets subjected to deuterium, or argon, plasma is compared. Erosion by deuterium plasma results in the development of a cone-like surface morphology and the resultant measured erosion rate is almost an order of magnitude less than expected from sputtering calculations. The morphology that develops has been characterized as a function of incident ion energy and fluence to the target. The sputtering yield measured from targets exposed to argon plasma agrees with sputtering calculations and no surface morphology is observed after the exposure. A simulation of the sputtered atoms ejected into the plasma column is developed in order to understand the changing axial penetration distance measured spectroscopically as the morphology emerges. Redeposition of atoms sputtered at shallow angles on adjacent cone structures can result in a lower erosion rate and can account for an increase in the axial penetration distance of atoms into the plasma. (paper)