Spurious oscillations affecting FIR polarimetry measurements

Polarimetry measurements of Faraday rotation on Tore Supra are systematically affected by spurious oscillations that may seriously hinder the reconstruction of plasma current profiles. The same behavior has also been regularly observed on other experiments, such as JET and as RFX. Causes of this phe...

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Bibliographic Details
Published in:Review of Scientific Instruments 2004-10, Vol.75 (10), p.3405-3407
Main Authors: Elbèze, D., Gil, C., Giannella, R., De Pasqual, L.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AMPLITUDES
ELECTRIC CURRENTS
ELECTRIC FIELDS
ERRORS
FARADAY EFFECT
OSCILLATIONS
PLASMA DIAGNOSTICS
PLASMA JETS
PLASMA WAVES
POLARIMETERS
POLARIMETRY
POLARIZATION
STRAY RADIATION
TORE SUPRA TOKAMAK
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Summary:Polarimetry measurements of Faraday rotation on Tore Supra are systematically affected by spurious oscillations that may seriously hinder the reconstruction of plasma current profiles. The same behavior has also been regularly observed on other experiments, such as JET and as RFX. Causes of this phenomenon are interferences between the probing beam and stray radiations having the same frequency. It perturbs the intensity of the signals from the detectors installed on the two orthogonal polarization channels. Experimental tests confirm the dependence of the oscillation amplitudes on the Faraday angle as predicted by the analytical and numerical description of the phenomenon. Special care must be taken to eliminate stray beams: When the stray beam polarization is parallel to the incident one, a relative ratio of the electric field amplitudes
ISSN:0034-6748
1089-7623
DOI:10.1063/1.1786637