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

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 H2 as opposed to D2. This observation supports the model that all of the neutral D2 gas enters the plasma region, strikes the plasma first, and is dissociated. The part of the D2 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 H2 instead of D2 wall loading in TMX-U