SCREENING OF RECYCLING AND NON-RECYCLING IMPURITIES IN THE ALCATOR C-MOD TOKAMAK

The behavior of argon and nitrogen, injected into single null diverted Ohmic discharges, has been compared. The screening of the divertor an d scrape-off layer plasma is studied by comparing the number of impuri ty atoms in the core with the number injected by a calibrated gas puff . The effect of the poloidal position of injection on screening has be en investigated. The core nitrogen density is dependent of an poloidal position of injection while the argon density is not. The spatial dis tribution of low charge states in the divertor has also been studied u sing a multichord visible spectrometer. Initial results of nitrogen mo deling with the Monte Carlo code DIVIMP are presented.