05aE09P
ヘリオトロン J における遠赤外線レーザー干渉計の開発
Development of Far Infrared Laser Interferometer in Heliotron J
大谷 芳明 1, 大島 慎介 2, 史 楠 2, 秋山 毅志 3, 南 貴司 2, 田中 謙治 3, 長崎 百伸 2,
水内 亨 2, 小林 進二 2, 岡田 浩之 2, 門 信一郎 2, 山本 聡 2, 釼持 尚輝 1, 臧 臨閣 1,沙 夢雨1, 笠嶋 慶純1, 原田 伴誉1, 佐野 匠1, 野口 直樹1, 丸山 正人1, 桐本 充晃1,程 崧明1, 鈴木 文子1, 安枝 樹生1, 呂 湘浔1, 木島 滋2, 中村 祐司2, 佐野 史道2
OHTANI Yoshiaki1, OHSHIMA Shinsuke2, SHI Nan2, AKIYAMA Tsuyoshi3, MINAMI Takashi2 et al.
1京都大学エネルギー科学研究科, 2 京都大学エネルギー理工学研究所,
3
自然科学研究機構核融合科学研究所

1Graduate School of Energy Science Kyoto University, 2 Institute of Advanced Energy Kyoto University,
3
National Institute for Fusion Science

Recently, high density plasma production with ne>1020 m-3 was successfully achieved with advanced
fueling control techniques such as Supersonic
Molecular Beam Injection (SMBI) and short-pulsedHigh Intensity Gas Puff (HIGP) in Heliotron J [1, 2].
For the study of such high density plasma production,
a Far InfraRed (FIR) laser interferometer is being
developed, which utilizes short-wavelength waves
compared with that of a microwave interferometer
being used in Heliotron J.
Figure 1 shows a schematic view of theMichelson interferometer constructed on Heliotron J.
This system uses an HCN laser (λ = 337 μm, outputpower = 30 mW) as the light source. Two laser beamlines are used in this system. One of the laser beams
is injected into the vacuum chamber as a probe beamfrom a lower port and is reflected back with a cornercube mirror located at an upper port. The frequencyof the other beam is shifted by 1.45 MHz with aSuper Rotating Grating (SRG) [3] for heterodyne
detection. These two beams are mixed and detectedwith Schottky barrier diodes and the resultant beatfrequency is 1.45 MHz, which can realize a hightime resolution faster than 1 μs.

The influence of refraction of the probe beam isinvestigated in this system using a ray tracing code,
TRAVIS [4] since the refraction makes the laser
beam deflected from the original axis and degrades asignal level significantly at the detector. Assuming
several types of electron density profiles as shown inFig. 2 (a), horizontal deviations at several importantcomponents, e.g. the corner cube mirror, the beamsplitters, the vacuum windows and the detector wereevaluated. The estimated beam deflection at these
optical components is small enough compared withthe beam diameter and is negligible. At the detector,
the deviation is less than 15 mm in case of ne(0) =1×1020 m-3 as shown in Fig. 2(b), however the two
beams can still overlap since the beam diameter atthe detector is roughly 40 mm. Therefore, highdensity plasmas produced by SMBI or HIGP can beconsidered to be measureable using this system inHeliotron J although sufficient laser power isrequired to increase signal-to-noise ratio.
The details of FIR interferometer system and therefraction effect will be shown and discussed.

Fig. 2 : (a) Electron density profiles assumed in
TRAVIS calculation. Exp. is a fitted curve of anexperimental data.
(b) Beam axis deviation at the detector of probebeam. The yellow line indicates the beam diameter atthe detector.
[1] T. Mizuuchi, et al. J. Nucl. Mater., 415 (2011) 443[2] S. Kobayashi, et al. Proc. 40th EPS Conf., 1-5 July (2013)P1.148

Fig. 1: Conceptual scheme of FIR laserinterferometer in Heliotron J[3] T. Maekawa, et al. Rev. Sci. Instrum. 62, 304 (1991)[4] N. B. Marushchenko, et al., Plasma Fusion Res. 2 (2007) S1129