Measurement of fast changes of the edge density profile in TEXTOR

The determination of the spatial distribution of the electron density in the boundary layer of a plasma is of importance for the investigation of plasma-wall interactions in plasma devices. Atom beam techniques are suitable diagnostics to determine electron density profiles in the edge plasma of a tokamak. Spatial observation of the visible light emitted by excited atoms due to electron collision allows the determination of the electron density profile as an absolute quantity if the light emission is recorded up to the total absorption (ionization) of the beam. At TEXTOR the emitted spatial density profile is usually recorded by photosensitive linear arrays, having an integration time of τ ≥ 0.5 ms. Fast changes of the edge density profile whose observation is of importance, e.g. for fluctuations, disruptions or investigations of H-mode transitions, cannot be measured with such an integration time. Moreover, in the case of atom beams which are generated by the laser blow off technique only one density profile per laser shot can be obtained. In order to improve the time resolution and to increase the number of measured profiles with the laser blow off equipment of TEXTOR a CCD-camera with big frame rate (36.8 kHz, τint = 27.2 μs) has been designed. First measurements with this diagnostic on TEXTOR will be reported. (author) 2 refs., 4 figs., 1 tab