Edge parameters from an energy analyzer and particle transport on TEXT-U

The energy distributions of ions and electrons in the scrape-off layer of TEXT are measured with a bidirectional retarding field analyzer (RFA). The probe provides simultaneous measurements parallel and antiparallel to the plasma current. Large asymmetries in this direction in the flux and temperature that were found with the RFA appear partly due to differences in the connection lengths Lc. The measurements from the analyzer are compared with the results of a simple edge model to infer the edge particle diffusion coefficient. While the measurements are consistent with the model for longer connection lengths (∼10 m in TEXT-U), the agreement deteriorates for shorter Lc.