Aachen PK 2003 – scientific programme
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P: Plasmaphysik
P 7: Plasma Diagnostics
P 7.6: Talk
Tuesday, March 18, 2003, 17:10–17:30, FO1
Spatially Resolved Fast Swept Langmuir Probe Measurements at the Wendelstein 7-AS stellarator — •Martin Schubert and Michael Endler — Max-Planck Institut für Plasmaphysik, EURATOM Association, Garching, Germany
Stationary Langmuir probe measurements of ion saturation current and floating potential cannot give direct information on density and plasma potential fluctuations in the presence of temperature fluctuations. This problem can be avoided if the probe bias voltage is continuously swept faster than the fluctuation time scale, recording the current-voltage characteristic. This paper reports high resolution (1µ s,2 mm) measurements of probe characteristics in the scrape-off layer of W7-AS by means of a Langmuir probe array with 15 fast swept (1 MHz) tips. In the analysis, the data are corrected for stray and polarization currents 11, as we apply combined high frequency response and probe theory. We use ion saturation current, floating potential and electron temperature as fit parameters and calculate density and plasma potential. The simultaneous measurement of all these quantities is important for the comparison with turbulence models. In a correlation analysis we find structures in the electron temperature similar to those in density and potential with a typical lifetime of ∼ 30 µs and a poloidal scale length of ∼ 2.5 cm .
11 A.V.Nedospasov et al., Contrib. Plasma Phys. 34 (1994) 478