Initial alt-i pump limiter studies on TEXTOR

The ALT-I pump limiter has been used to control the fueling and recycling characteristics of TEXTOR during stable, reproducible tokamak discharges. The module has been operated in three modes: (1) Normal Limiter, with no particle collection, (2) Particle Scoop, with a maximum approx. 2 x 10/sup -3/ torr pressure rise in the 700 liter unpumped collection chamber, and (3) Pump Limiter, with up to approx. 10,000 1/s pumping speed and particle removal rates of up to 6 x 10/sup 20//s. In a comparison of operation in modes (1) and (3) using identical gas fueling programs, the total core electron number decreased by as much as 50%. The effective TEXTOR particle confinement time, tau/sub p/* = tau/sub p//(1-R), was decreased by a similar ratio. Within the throat region, during typical operation, electron densities and temperatures were 6 x 10/sup 11/ to 2 x 10/sup 12//cm/sup 3/ and 15 to 30 eV. These conditions are representative of an operating regime in which there is high reionization of neutrals, but no change in incoming plasma parameters in the throat region. Energetic particles near the deflector plate were observed. During a gradual insertion of TiC-coated ALT-I beyond the stainless steel TEXTOR main limiters, themore » density of Ti in the plasma increased to a level similar to those of Cr and Fe. The gas injection fueling efficiency while puffing hydrogen directly into the plasma at the pump limiter tangency point was measured to be > 0.9. These results are discussed in conjunction with measurements of particle flows within ALT-I and other plasma diagnostics to characterize pump limiter operation on TEXTOR.« less