Abstract
First results from a movable Langmuir probe at the midplane of Asdex Upgrade are presented. We give a short description of the instrument and discuss the data evaluation. Langmiur probe interpretation is based on a nonlinear fit to an asymmetric double probe characteristic. Obtained radial profiles are compared with results of the Li-beam and ECE diagnostics. A comparison with a scrape off layer decay length scaling for JET shows good agreement for low plasma densities, but significant deviations for high densities. Finally we show data obtained using a self emitting probe. This technique allows a direct measurement of the plasma potential close to the separatrix. The difference of floating and plasma potential is used for electron temperature determination. The results are in close agreement with the temperature derived directly from the Langmuir probe characteristics. Close to the separatrix a radial electric field of 70V/cm can be derived from the measured plasma potential.
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