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P: Plasmaphysik

P 8: Plasma-Wand-Wechselwirkung I

P 8.4: Fachvortrag

Dienstag, 9. März 2004, 16:25–16:45, H\"orsaal D

Observation System of a Modulated Supersonic Helium Beam for the Measurement of T_e and n_e Fluctuations — •U. Kruezi, B. Schweer, G. Sergienko, B. Unterberg, and U. Samm — Institut für Plasmaphysik, FZ Jülich, EURATOM-Association, Trilateral Euregio Cluster, 52425 Jülich, Germany

A supersonic helium beam diagnostic has been developed for fluctuation measurements in the boundary plasma of TEXTOR. The ratios of three helium line intensities at 667.8 nm, 706.5 nm and 728.1 nm are used for the determination of the electron temperature T_e and density n_e. The beam injection system was developed with respect to a low beam divergence necessary for the measurements of expected wave number spectra up to k_r=3 mm⁻¹ and fluctuation frequencies up to ν=100 kHz. The beam observation system consists of two complementary units. In the first system the three emission profiles are recorded simultaneously at the required wavelengths selected by interference filters. The light is combined in a imaging light guide to one camera (integration time 10  ms). The second system is made up of three 32-Channel Photomultiplier tubes (PMT). Each PMT covers the same radial range and the data acquisition system permits to take the signals of eight spatial channels simultaneously. A multiplexer system switches between channels within one plasma discharge for a flexible correlation analysis of the total spatial range observed. A new PMT electronics operates at a low noise level of 5 mV compared with the full amplitude of 2 V and is therefore sufficient for the measurement of relative fluctuation amplitudes down to 0.2−1.0%. The fast signals are relatively calibrated to that from the slow system.