30D32P
LHD偏光マルチパストムソン散乱計測システムの開発
Development of the polarization multi-pass Thomson scattering system inLHD
安原亮1, 山田一博1, 吉川正志2, 波多江仰紀3, 谷塚英一3,林浩1, 舟場久芳1
R. Yasuhara1, I. Yamada1, M. Yoshikawa2, T. Hatae3, E. Yastuka3, H. Hayashi1, H. Funaba1
1

核融合研、2筑波大学、3原子力機構
1
NIFS, 2Tsukuba Univ., 3JAEA

Thomson scattering (TS) diagnostics is one of themost reliable methods for determining the local
electron temperature (Te) and density (ne) in fusion
plasmas. However, due to the small Thomson
scattering cross-section, TS measurements arechallenging for low densities plasmas. To increase
the scattering probability at low densities, amulti-pass TS scheme is effective, which allows alaser pulse to be focused several times into thescattering volume, thus increasing the scattering
photon number. In addition to improving thesignal-to-noise ratio, a multi-pass TS system can beused to improve the time resolution and expand themeasurable range of Te.
Multi-pass TS systems are demonstrated atmany institutes. TEXTOR group has demonstrated
the improvement of signal to noise ratio by use ofmulti-pass TS system which uses a pair of concave
mirror for recycling photon [1]. JT60 TS group hasconstructed a double pass system by the use of aphase conjugate mirror [2]. Although previous
multi-pass systems have increased the reliability,
they are also limited by the optical system, e.g., aseach laser beam pass is different in aconcave-mirror-type TS system (the TEXTORsystem), the scattering volume should be set so that
it is near the focal point of the concave mirror, else
it is necessary to calibrate the system for eachdifferent beam pass. The phase conjugate mirror
system, however, requires purity in the laser
bandwidth.
In this study, we propose a newly scheme ofmulti-pass TS system by the use of a polarization
optics. This scheme can be modified from the basic
single pass TS system by adding the high reflection
mirror for cavity mirror, lenses used for image
relaying the laser beam and polarization control
devices of a Faraday rotator and a Pokel’s cell. It
has a collinear beam line in the multi-pass cavity.
The system design is carried out by polarization
analysis by Jones matrix and optical ray trace.
To evaluate the effect of the multiplication of
the scattering light, a multi-pass system without apolarization control device was installed in theGAMMA 10 system. As the result, the integrated
scattering signal of the double-pass configuration isabout 2 times larger than that of the single-passconfiguration.
Now, we are constructing this system for theLHD TS system. Laser light is focused into theplasma by the first convex lens via 4-O port laser
window. After interaction with the plasma, laser
light is emitted from the 4-I port window, which
has an anti-reflection coating, and is collimated by
the second convex lens. After that, Laser light isreflected by a mirror for the second pass and again
focused into the plasma. Figure 1 shows theRayleigh scattering signals at the double passconfiguration of the LHD TS system. We canconfirm two peaks of Rayleigh scattering signal
from the first pass and the second pass.
In this presentation, we show the results of thedetailed design and experimental data of the new
TS system configuration.

Fig.1 Rayleighen scattering signal at the doublepass configuration of the LHD TS system[1]. M Yu Kantor, et al. Plasma Phys. Control.
Fusion 51 (20e09) 055002.
[2]. T. Hatae, O. Naito, M. Nakatsuka, and H.
Yoshida, Rev. Sci. Instrum. 77, (2006)
10E508.