22P110-P
Present status of the Nd:YAG Thomson scattering measurement
system development for time evolution measurement of plasma profile
on Heliotron J (2)プラズマの分布時間発展計測
プラズマの分布時間発展計測のための分布時間発展計測のための Nd: YAG トムソン散乱計測
トムソン散乱計測装置開発の装置開発の現状(2)現状
Shohei Arai1, Takashi Minami2, Naoki Kenmochi1, Hiroaki Yashiro,1 Chihiro
Takahashi2, Shinji Kobayashi2, Tohru Mizuuchi2, Shinsuke Ohshima3, Satoshi
Yamamoto2, Hiroyuki Okada2, Kazunobu Nagasaki2, Kiyofumi Mukai1, Hyunyong Lee1,Linge Zang1, Tasuku Kagawa1, Koji Mizuno1, Takayuki Minami1, Hiroto Watada1,Yoshinobu Wada1, Yuji Nakamura2, Kiyoshi Hanatani2, Shigeru Konoshima2,Fumimichi Sano2
荒井翔平 1, 南貴司 2, 剱持尚輝 1, 八代浩彰 1, 高橋千尋 2, 小林進二 2, 水内亨 2,
大島慎介 3, 山本聡 2, 岡田浩之 2, 長崎百伸 2, 向井清史 1, 李炫庸 1, 臧臨閣 1,香川輔 1, 水野浩二 1, 南貴之 1, 和多田泰士 1, 和田善信 1, 中村祐司 2, 花谷清 2,木島滋 2, 佐野史道 2
1Graduate School of Energy Science,Kyoto University,Gokasho,Uji 611-0001,Japan京都大学エネルギー科学研究科 〒611-0001 宇治市五ヶ庄
2Institute of Advanced Energy Science, Kyoto University,Gokasho,Uji 611-0001,Japan京都大学エネルギー理工学研究所 〒611-0001 宇治市五ヶ庄
3Pioneering Research Unit for Next Generation,Kyoto University, Gokasho,Uji 611-0001,Japan
京都大学次世代研究開拓ユニット 〒611-0001 宇治市五ヶ庄
We are developing a new high repetition rate Nd: YAG Thomson scattering measurement system for
Heliotron J. In this paper, we report design studies of the collective lens design and the high-speed dataacquisition/analysis system. The former reduces heat load to the vacuum window by the laser beam andconverges in plasma region due to improve spatial resolution. The latter system can collect and analyze
the data with no delay right after the plasma discharge.

1. Introduction
To investigate improved plasma confinementmode, we need to know the temperature and density
profiles and their time evolution. We are developing
a new high repetition rate Nd: YAG Thomson
scattering measurement system for Heliotron J. In
Heliotron J, there is already TV Thomson scattering
measurement system. It uses the high power rubylaser and only shoots a single shot so it can’tmeasure time evolution. Nd: YAG Thomson
scattering measurement system uses high repetition
rate Nd: YAG lasers, so this makes it possible tomeasure the time evolution of plasma
density/temperature profile1, 2.
2. Development of the laser transmission system
Figure 1 illustrates the laser transmission system
for Heliotron J. It shows the two Nd: YAG lasers
refracted by the refraction mirror, the laser beam go
through the extension pipes and the lasers crosses
inside the vacuum vessel, the Heliotron J. The laser
which did not be scattered goes straight ahead to thebeam dump and be absorbed. The laser transmission
system is composed by two Nd: YAG lasers, aHe:Ne laser, refraction mirrors, a collective lens.
The power of each Nd: YAG laser is 550mJ. The
He: Ne laser is a visible laser and it is used for theaxis alignment. We have to use some refraction
mirrors to lead the laser beam into the vacuum
vessel. We have to design the collective lens toconverge the laser beam at the plasma cross-section.
On developing the laser transmission system, we
have to consider two issues. The first is to get ahigh S/N ratio by reducing the stray light level. We
designed to set the entrance/exit vacuum windowsfor the laser beam from the plasma as far as
possible by using extension pipes. We designed
these pipes not to be interfered with the structure of
Heliotron J and to keep the length from the vacuum
vessel as long as possible. The second is to design
the beam diameter. Since the Nd: YAG laser beam
is so powerful, it may break the vacuum window
because of its local heat load if the beam diameter is
too small. On the other hand, to realize a high22P110-P
enough spatial resolution of the measurement
measuremensystem, the beam diameter should be kept narrow
enough when the laser beam passes through theplasma. Therefore, we have to optimize thecollecting lens design to satisfy these requests
simultaneously.
In order to design the collective lens, it isnecessary to check the beam divergence. Figure 2
shows the laser beam diameter for the two lasers asa function of the distance from the laser body. We
checked the beam diameter with the laser alignment
papers. We exposed the paper to the laser beamwith 10cm interval. The result iss the beam diameter
gradually decreases as a function of the distance. To
focus the beam at the plasma center,, we designed acollective lens using the data of the laser beamdiameter.

We decided to introduce the Time Invariant Method(TIM) which can collect data within affixed time
without
thout command of OS. We are developing a dataacquisition/analysis system which can process thehigh-speed scattering light signals
signal based on CINOS.
CINOS is an experimental data processing system,
which has a multi-computing
computing feature, can process
input-output and computing with a given linear time.
The output time depends on the acquisition time, soon usual computer, if the acquisition time delays,
the output time will delay too. Additionally,Additionall if thedelay of output time takes time until the next
discharge, the data of that discharge could not betaken. But TIM finishes collecting data in a fixedtime, so the output time will also be constant and it
is a system that would not effect on plasma
discharge3.

Fig.1 Schematic of the laser transmission system

4. Summary
We are developing the new high repetition rate
Nd: YAG Thomson scattering measurement system
for Heliotron J to measure the time evolution ofelectron temperature and density of plasma profile.
This is because in investigating thermal transport,trait
is important to know the time evolution of electron
temperature and density of plasma profile.
To realize a high S/N ratio, we designed andmade an optimized laser transmission system. Asfor the data acquisition
tion system, we are developing a
new system using CINOS and TIM.
Acknowledgment
The authors are grateful to the Heliotron J
technical team for their excellent arrangement ofthe experiments. This work was partly supported byNIFS/NINS under the NIFS Collaborative Research
Program (NIFS04KUHL005).

Fig.2 The laser beam diameter as a function of thedistance from the laser

3. Development of the data acquisition system
On running plasma experiment efficiently, it isimportant to check result of the Thomson scattering
measurement as soon as possible and to decide next
discharge condition. In a usual data processing
device, however, there are some cases
case where thedata acquisition and analysis does not complete bynext discharge. This happens because of thescheduling and interrupt feature of computer OS.

Reference1T. Minami et al: Rev.Sci. Instrum. 81 (2010)
10D532
2
M. Yokoyama: Plasma fusion academy journal
nunber76 issue 11(2000)
3
C. Takahashi et al:: About timing critical signal
processing. Kyoto University
niversity technique collegium(2009)