SPUTTERING OF PLASMA-FACING MATERIAL BY SIMULTANEOUS BOMBARDMENT WITHCARBON AND DEUTERIUM IONS

The sputtering of material (C, Si, and W) exposed to a plasma with an electron temperature of 40 eV containing deuterium ions and carbon ion s has been investigated using the computer program TRIDYN. The sputter ing yields for the various elements were calculated dependent on the p lasma ion fluence and the carbon concentration in the plasma. The ques tion, whether erosion of the target material or deposition of the carb on atoms occurs, strongly depends on the carbon concentration in the p lasma and the target atom species. Also a transition from a erosion ph ase to a deposition phase (and also reversed) during the exposure was observed under certain conditions. Steady state conditions were achiev ed only in a time scale which is of the same order as the discharge ti me in today's fusion experiments. An analytical model has been develop ed and the results agree well with those obtained by computer simulati ons.