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  • Construction and testing of a repeating laser blow-off system for examining electrostatic electron-density fluctuations in the boundary and peel layers of TEXTOR and Wendelstein 7 AS


This project's aim was to determine to what extent Li-beams that are produced by means of laser blow-off (LBO) can be used for the investigation of fluctuations of the electron density in the edge and scrape-off layer of fusion devices and to carry out fluctuation measurements. For this purpose, the LBO-system installed on the TEXTOR tokamak has been upgraded for repetitive operation and used for fluctuation measurements on TEXTOR and on the Wendelstein 7-AS stellarator.

On the basis of TEXTOR discharges it is shown for the first time that this diagnostic can indeed be used for the investigation of fluctuations of the electron density in fusion devices. However, if the temporal variation of the Li flux is too pronounced on time scales that are short compared to the duration of the LBO pulses, the distinction between correlations that arise from plasma fluctuations and those that arise from variations of the Li flux can be difficult or even impossible.

On Wendelstein 7-AS, this method has been shown to be a useful tool for the investigation of fluctuations. There, it was used in combination with other diagnostics to get new information on the structure of the fluctuation cells.

In some discharges, a strong distinction between fluctuations in the core plasma and in the scrape-off layer could be seen. In the latter, the measured radial velocity is observed to drop with rising density. On the basis of discharges with different orientation of the magnetic field, interpretations of the observed radial velocity are discussed.

Additional information

Authors: BRUCHHAUSEN M, Institut für Plasmaphysik, EURATOM Association, Trilateral Euregio Cluster, Forschungszentrum Jülich, Jülich (DE)
Bibliographic Reference: Berichte des Forschungszentrums Jülich no. 3993, June 2002, pp.169. Free of charge
Availability: Available from Forschungszentrum Jülich GmBh - Zentralbibliothek Tel: (+49) (2461) 61-5220 Fax: (+49) (2461) 61-6103 E-mail:
ISBN: ISSN: 0944-2952
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