Plasma and Fusion Research

Volume 14, 1402072 (2019)

Regular Articles

Improvement of Aperture Configuration to Reduce the Stray Light for Thomson Scattering Measurement Using a Peripheral Beam Profile Monitor
Yuya KAWAMATA, Akira EJIRI, Kyohei MATSUZAKI, Yuichi TAKASE, Naoto TSUJII, Takumi ONCHI1) and Yoshihiko NAGASHIMA1)
The University of Tokyo, Kashiwa 277-8561, Japan
Kyushu University, Kasuga 816-8580, Japan
(Received 16 January 2019 / Accepted 11 March 2019 / Published 11 April 2019)


The stray light is a major problem in Thomson scattering (TS) measurements. The main cause of stray light is unnecessary divergence of the incident laser beam and an aperture is a standard component to reduce it. In order to improve the aperture configuration (including size, number and position in the laser injection tube), a peripheral beam profile monitor, consisting of a screen with a through hole for the laser beam and a CMOS camera, was developed. Instead of the actual laser injection tube a mock-up tube was used to measure the peripheral beam profiles under various aperture configurations. The configuration with four 15mm diameter apertures was chosen and installed on the TS system for the TST-2 spherical tokamak. The stray light was reduced to about 4% compared to the smaller diameter injection tube with no apertures. As a result, it became possible to make TS measurements in the electron density range above 1.0 × 1017 m−3.


Thomson scattering, stray light, diagnostic, TST-2, spherical tokamak

DOI: 10.1585/pfr.14.1402072


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