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Diagnostics allowing a non-perturbative knowledge of the parameters are required if the plasma performance in controlled fusion experiments is to improve. Coherent, or collective, scattering is created by the collective movements of electrons in the plasma. The density fluctuations can be considered as a set of waves in the plasma having broad spectra both in frequency and wave vector. Radiation, scattered in a given direction by electrons oscillating in the incident coherent beam's electromagnetic field, provides a detector current proportional to a component of the spatial Fourier transform of fluctuations contained in the plasma cylinder crossed by the beam. The broadening of the scattered wave also gives information on the ion temperature and it can be shown that the scattered power spectrum and the electron density fluctuations spectrum are identical. By changing the detector's orientation, turbulence corresponding to the wave vector can be measured and, using Fourier transform, the frequency spectrum can be obtained from the time dependent signal. The total density fluctuation level can then be obtained. This paper discusses the techniques used in detection, wavelength selection, beam separation, spatial resolution improvement and signal analysis, and presents the results obtained.

Additional information

Authors: LAVIRON C, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Paper presented: IVth Workshop on Magnetic Confinement Fusion, Santander (ES), June 22-26, 1992
Availability: Available from (1) as Paper EN 37077 ORA
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