MOLECULAR IMPURITIES IN ASDEX UPGRADE PLASMA DISCHARGES

The introduction presents a historical review of the role of molecules in tokamak research starting from the first installations at the Kurc hatov Institute. Molecular impurities were mostly considered as a tran sient conditioning problem, but with the use of carbon for wall and li miter elements, it was perpetuated. New results about the elementary p rocesses involved in hydrogenic carbon erosion are reported and the ex isting data base is briefly discussed. Results from mass spectrometry are presented as well. as data from optical spectroscopy including det ermination of CD4 and CD fluxes from molecular band intensities. A typ ical yield of about 5% for hydrogenic chemical erosion is obtained. In combination, all these results show the impact of hydrogenic carbon e rosion. They strongly suggest that with boronized walls it remains as the dominating process for the carbon fluxes in the SOL and even domin ates the carbon concentration in the central plasma in spite of a high SOL screening action for hydrocarbons.