Extinction of CD band emission in the divertor of ASDEX Upgrade

We found a complete extinction of the CD molecule emission in the inboard d ivertor of ASDEX Upgrade at high density with the transition to a recombini ng divertor plasma, The electron temperature in the recombining divertor pl asma ranges from 1.2 down to 0.3 eV. Two effects may explain the extinction at such low temperatures, (1) a steep decay of the yield for chemical sput tering as theoretically predicted and (2) a suppression of the optical emis sion while the methane molecules dissociate unchanged via charge exchange. (C) 2001 Elsevier Science B.V, All rights reserved.