Spectroscopic investigation on the impurity influxes of carbon and siliconin the ASDEX upgrade experiment

Emission profiles of carbon and silicon along the heat shield (HS) were mea sured before and after siliconization of the vessel. Siliconization does no t affect the divertor and therefore large changes in impurity concentration s and influxes cannot be attributed to it. A strong transient increase of t he silicon concentration was observed immediately after the siliconization lasting for a few discharges. However, no large change was observed in the silicon influx from the HS, excluding it as possible source of the concentr ation increase. The fast decrease in the silicon concentration can be attri buted to strong erosion at the outer limiter. The impurity influxes for C2 and Si2+ from the HS ale estimated and compared with the corresponding cor e concentrations. The relative contribution to the plasma impurity content from divertor, HS and outer protection limiter is discussed. Zeeman splitti ng analysis permits one to identify the emitting region of carbon radiation . Anomalously high silicon sputtering yields are measured, which do not how ever cause high core silicon content. (C) 2001 Elsevier Science B.V. All ri ghts reserved.