Local neutral particle density in the W7-AS stellarator

Ion temperatures as obtained from line integrated CX-flux measurements generally must be corrected for systematic errors by a reconstruction technique /1/ which employs measured ne, Te and Zeff profiles and a neutral density n0 profile which is calculated from a Monte-Carlo transport code /2/. The reconstruction technique is an iteration which starts from the non corrected ion temperature profile as obtained from the line-averaged passive fluxes. This non corrected ion temperature will be called passive ion temperature in the following. For the reconstruction technique the knowledge of the neutral particle density profile is very important. Reliable estimates of the neutral densities in the toroidal section of the stellarator W7-AS where the CX measurements are made, are not available from the DEGAS code /3/. This is due to the poor knowledge of the neutral density sources, which in this region are essentially determined by strongly asymmetric wall recycling. By using a diagnostic beam of fast neutrals a space resolved measurement of the ion temperature profile is obtained. This active ion temperature profile together with the line integrated fluxes and the passive ion temperature allows an estimate of the neutral particle density and its profile. For this analysis the following steps are required and will be described in detail. (orig.)