Chemical sputtering yields of carbon based materials at high ion flux densities

Graphite and advanced carbon fiber composites (CFC) are widely used inside the vacuum vessel of magnetic fusion devices. However, erosion by chemical sputtering via hydrocarbon formation might limit their application as target material in future machines like ITER. The first systematic study of the chemical erosion of graphite and different CFCs (including a silicon-doped one) as a function of ion flux density in the range of 1.4 x 10(21)-5 x 10(22) m(-2) s(-1) was performed in the plasma generator PSI-1. The results of three different analysis methods agree within about 40%. No differences in the chemical erosion yields between hydrogen and deuterium exposures are found for the various materials. In contrast, the erosion yields differ up to a factor of two for the different CFC-materials. In general the chemical sputtering yields decrease with increasing ion flux density Gamma according to Gamma(-0.6) reaching levels below 1% at the highest fluxes. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) show preferred erosion in the area between the carbon fibers. (C) 1999 Elsevier Science B.V. All rights reserved.