Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
P: Plasmaphysik
P 12: Plasma Wall Interaction, Diagnostic and Low Temperature Discharges (Poster Session)
P 12.5: Poster
Freitag, 6. April 2001, 12:30–15:00, AT2
The effect of the safety factor on the transport properties in the scrape-off layer of TEXTOR — •M. Lehnen, M. Brix, and B. Schweer — Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Assoziation, Trilateral Euregio Cluster
Radial profiles of electron temperature Te and density ne in the plasma edge of TEXTOR are measured by the spectroscopic observation of a thermal helium beam at the low field side. The transport coefficients in the scrape-off layer can be deduced from the e-folding length of the plasma parameter.
The dependence of the edge parameters and the transport coefficients on the safety factor q is discussed. The safety factor qa at the last closed flux surface (LCFS) has been varied from approximately 3 to 5 by a variation of either the plasma current IP or the toroidal field strength Bφ. It is shown, that ne(a) at the LCFS depends strongly on IP - indicating a change in the radial transport inside the LCFS - but keeps constant during a variation of Bφ. Te(a) is constant for both parameters. The density e-folding length λn in the scrape-off layer is only determined by the connection length i.e. the safety factor; a variation of the diffusion coefficient with qa is not observed.
For all achieved q-values the influence of a magnetic field reversal on the edge parameters and the e-folding length is investigated. The reversal leads to an inversion of the radial particle drifts. This causes a change in λn of about 15%. The diffusion coefficient in a discharge with reversed field is therefore about 30% higher due to the increased transport caused by the radial drift motions.