Plasma edge transport phenomena caused by particle drifts and sources in TEXTOR

The parallel and radial transport properties of the plasma edge of TEXTOR are studied using radial electron density and temperature profiles as well as ion temperatures and poloidal velocities in the scrape-off layer (SOL). These quantities are measured by thermal helium beams at the low (LFS) and high field side (HFS) by emission and beam driven charge exchange recombination spectroscopy. We investigate the influence of the safety factor and of a magnetic field reversal on these edge parameters. Especially the field reversal leads to clear effects: a decrease of the density at the LFS, a significant change in the poloidal density distribution, which is identified by comparing LFS and HFS densities, and an increase in the density e-folding length at both poloidal positions. The poloidal ion rotation changes sign in reversed field configuration and thus gives a hint on the role of poloidal drifts in the SOL. For further analysis, we present a simple fluid model including poloidal drift velocities and local ionization sources. With this model we can show that the poloidal E×B drift clearly influences the poloidal density distribution. However, although the model results show the same tendencies as the experimental findings, the impact of the field reversal on the density asymmetry is not that pronounced as in the experiment. The dependence of the density e-folding length on the poloidal and radial drifts as well as on the source distribution is discussed within the frame of analytical estimates.