Experimental determination of the contribution of chemical sputtering of carbon on carbon core concentrations

The effects of a methane puff at three different plasma locations has been compared with a similar deuterium puff in a 2.5 MA, 2.5 T Elmy H-Mode. Chan ges in edge and core spectroscopic signals have been examined, and show tha t divertor methane sources are much better screened than wall sources. The intrinsic chemically sputtered methane source from the outer divertor is de rived, and shown to account for only about 15% of the carbon in the plasma core. Modelling with EDGE2D/DIVIMP, using 0.5 eV carbon atoms for the metha ne source, has been performed and compared with the experimental results. T he model is found to correspond to the experimental trends, but it underest imates the screening of the wall methane source and overestimates the scree ning of methane in the divertor. (C) 1999 JET Joint Undertaking, published by Elsevier Science B.V. All rights reserved.