Conceptual design of a polarimetric Thomson scattering diagnostic in ITER

Polarimetric Thomson scattering (TS) is a novel diagnostic technique proposed as an alternative to conventional (spectral) TS, for the measurement of the electron temperature T sub(e) and density n sub(e) in very hot fusion plasmas. Contrary to spectral TS, which is based on the reconstruction of th...

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Bibliographic Details
Published in:Journal of instrumentation 2016-01, Vol.11 (1), p.C01071-C01071
Main Authors: Giudicotti, L., Bassan, M., Orsitto, F.P., Pasqualotto, R., Kempenaars, M., Flanagan, J.
Format: Article
Language:English
Subjects:
Depolarization
Diagnostic systems
Plasmas
Polarimetry
Scattering
Scattering angle
Spectra
Thomson scattering
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Summary:Polarimetric Thomson scattering (TS) is a novel diagnostic technique proposed as an alternative to conventional (spectral) TS, for the measurement of the electron temperature T sub(e) and density n sub(e) in very hot fusion plasmas. Contrary to spectral TS, which is based on the reconstruction of the Doppler broadened frequency spectrum, in polarimetric TS T sub(e) is determined from the depolarization of the scattered radiation. The technique is suitable for ITER, where it is expected to be competitive with conventional spectral TS for measurements in the highest T sub(e) range, specially in backward-like conditions with the scattering angle 90[degrees] [theta] [< or =] 180[degrees]. In this paper we consider a hypothetical polarimetric TS diagnostic for ITER and evaluate its performance for the [theta] = 145[degrees] scattering condition typical of the core TS system and also for a different scattering geometry in which, using a tangential laser beam, the central region of the ITER plasma can be observed under a scattering angle [theta] ~ 75[degrees]. In both cases we calculate the expected errors on the measured T sub(e) and n sub(e) that can be obtained with a simple, two-channel polarimeter, and taking into account that only a fraction of the TS wavelength spectrum is detected. In both cases the expected performances are compared with those of the conventional spectral core TS diagnostic to determine the plasma conditions in which the polarimetric technique is more advantageous. A measurement of the depolarization effect of the TS radiation using the JET High Resolution TS system of JET is also discussed.
ISSN:1748-0221
1748-0221
DOI:10.1088/1748-0221/11/01/C01071