[Table of Contents]

Plasma and Fusion Research

Volume 5, S2082 (2010)

Regular Articles

Development of a Bright Polychromator for Thomson Scattering Measurements
Akira EJIRI, Takashi YAMAGUCHI, Junichi HIRATSUKA, Yuichi TAKASE, Makoto HASEGAWA1) and Kazumichi NARIHARA2)
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan
1)
Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
2)
National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan
(Received 7 December 2009 / Accepted 4 March 2010 / Published 10 December 2010)

Abstract

A bright polychromator for compact, efficient YAG Thomson scattering measurement was designed on the basis of ray-tracing calculations. The optical input of the polychromator is a 2-mm-diameter optical fiber with a numerical aperture of 0.37. High refractive index glass lenses with monolayer anti-reflection coatings were used to reduce aberration effects and achieve good efficiency. A fast, low-noise detection system consisting of an avalanche photodiode and operational amplifiers was designed and tested using YAG laser pulses; the measured full width at half maximum (FWHM) of the laser pulse was 10 ns. The measured noise was dominated by the thermal noise of the input resistance R (= 470 Ω) when the signal was low, and the shot noise became dominant when the number of detected photons was greater than about 500.

Keywords

Thomson scattering, forward-backward scattering, polychromator, avalanche photodiode, spherical tokamak, non-inductive start-up, low density plasma

DOI: 10.1585/pfr.5.S2082

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This paper may be cited as follows:

Akira EJIRI, Takashi YAMAGUCHI, Junichi HIRATSUKA, Yuichi TAKASE, Makoto HASEGAWA and Kazumichi NARIHARA, Plasma Fusion Res. 5, S2082 (2010).