by or for the United States government is permitted. NEUTRAL PARTICLE DYNAMICS IN THE ALCATOR C-MOD TOKAMAK

An experimental study of neutral particle dynamics has been carried out over a wide range of operating conditions in Alcator C-Mod using special-purpose pressure gauges. Both divertor and mid-plane pressures are found to depend primarily on the edge plasma regimes defined by the scrape-off-layer heat transport. While the maximum divertor neutral pressure (30-60 mTorr) is achieved at high core plasma densities (iie=2-4x10 20 m-3), corresponding to the detached divertor state, the maximum ratio of divertor to mid-plane pressure (-70) is achieved in the high-recycling transport regime. Variations in the divertor geometry have a weaker effect on the neutral pressures. For otherwise similar plasmas the divertor pressure and compression are maximized when the strike point is located at the bottom of the vertical target plate. Modelling shows that the high pressure sustained during detached divertor operation (despite a considerable drop in the recycling source) can be explained by scattering of neutrals off the cold plasma plugging the divertor throat. Rev. 3.1 April 4, 1996Neutral Dynamics I I-