Aachen PK 2003 – scientific programme

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P: Plasmaphysik

P 17: Poster III

P 17.23: Poster

Thursday, March 20, 2003, 17:30–19:15, Foyer

Cotton-Mouton Polarimetry at the W7-AS Stellarator — •Kyu Dong Lee, Thomas Bindemann, Matthias Hirsch, and Hans Jürgen Hartfuß — Max-Planck-Institut für Plasmaphysik, EURATOM Ass., D-17491 Greifswald, Germany

The linear birefringence (Cotton-Mouton effect) of a magnetized plasma can be used to measure the line integrated electron density [1]. The Cotton-Mouton effect causes a phase difference Δ ϕ_CM ∝ ∫n_e B_⊥² dl between the two characteristic waves resulting in a change of the ellipticity of the probing wave.

The W7-AS stellarator offers unique sightlines suiteable for Cotton-Mouton Polarimetry: The actual position of the plasma has no influence on the measurement. The magnetic field component parallel to the direction of propagation (Faraday effect) is negligible. The perpendicular magnetic field is nearly constant. Thus the line integrated electron density is directly proportional to the phase shift caused by the Cotton-Mouton effect: ∫n_e  dl = const. B⁻² Δ ϕ_CM.

A Cotton-Mouton polarimeter working in the sub mm wave region had been implemented successfully at W7-AS [2]. This device was operated during the last experimental campaign of W7-AS in order to assist the line density measurements in high electron desity plasmas.

In this presentation the method of the measurement and the technique are reviewed. Recent experimental results are shown and discussed with respect to the problems occuring in high desity plasmas.

[1] S.E. Segre, Phys. Plasmas 3, 1182 (1996)

[2] Ch. Fuchs, H.J. Hartfuß, Phys. Rev. Lett. 81, 1626  (1998)