Neutral-fueling pressure measurements and modeling near the plasma edge in TMX-U. Revision 1

Large variations in pressure from external gas-fueling sources and from plasma-induced wall reflux along the TMX-U plasma have been observed. These pressure variations can produce locally high neutral density in the plasma, which strongly affects the plasma parameters. These local pressure measurements include data from a newly installed neutral-pressure diagnostic system of fast magnetron gauges. The plasma-induced warm-wall reflux has been observed to be primarily HD and H/sub 2/ as opposed to D/sub 2/. This observation supports the model that all of the neutral D/sub 2/ gas enters the plasma region, strikes the plasma first, and is dissociated. The part of the D/sub 2/ gas, which is not absorbed as ions, strikes a wall, where it is converted to HD. Electron induced wall desorption measured by a mass spectroscopy and actual analysis of the Ti indicates predominately H/sub 2/ instead of D/sub 2/ wall loading in TMX-U.