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Abstract

The phase contrast technique offers an attractive alternative to small-angle Thomson scattering for the investigation of plasma density fluctuations. This imaging technique converts small relative phase shifts into detectable intensity variations. A wave optics treatment is given and test results of a system built for the TCA tokamak are presented. The device is suitable for the study of density fluctuations in the wavelength range from 2 to 200 mm. It uses a low power continuous CO-2 laser probe beam of 15 cm width and liquid N-2 cooled HgCdTe detectors. For a 1 MHz bandwidth it allows detection of phase shifts as low as 3 x 10**-6 rad at the shot noise limit, corresponding to relative density variations DELTA-N - e/N-e approximately equal to 10**-4 for typical conditions in TCA.

Additional information

Authors: WEISEN H CENTRE DE RECHERCHES EN PHYSIQUE DES PLASMAS, ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE (SWITZERLAND), CENTRE DE RECHERCHES EN PHYSIQUE DES PLASMAS, ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE (SWITZERLAND)
Bibliographic Reference: INFRARED PHYSICS, VOL. 25 (1985), NO. 3, PP. 543-549
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