Kinetic modeling of plasma-limiter interaction in the TEXTOR edge region

Abstract

The plasma flow properties along a field line intercepting a limiter or other neutralizing surface are significantly altered through charge exchange and reionization of neutrals produced at the surface. This problem is investigated using a one-dimensional, steady state kinetic model. The collisional Boltzmann equation is solved for the ion, electron, and neutral particle distribution functions in one velocity variable as a function of distance from the neutralizing surface. The collisional operator in the Boltzmann equation includes the effects of charged particle collisions and calculates charge exchange and electron impact ionization rates through direct integration of the distribution functions. Results have been obtained for plasma conditions simulating those observed for ALT-I operation on TEXTOR. Spatial profiles of particle density, temperature, and presheath electric field strength on flux surfaces at various distances into the scrape-off are calculated. We find that neutral recycle reduces ion temperatures by as much as 30% as the plasma flows toward the neutralizing surface while electron temperatures remain unchanged. Collisional sources generate small presheath electric fields directed away from the limiter surface that have integrated potentials of only a few volts.