22P175-B
Observation of Fast Ion Velocity Distribution and Driven Waves by Collective
Thomson Scattering Diagnostic
協同トムソン散乱計測による高速イオン速度分布と駆動された波動の観測
Masaki Nishiura, Shin Kubo, Kenji Tanaka, Ryosuke Seki, Takashi Shimozuma, Takashi Mutoh,Kazuo Kawahata, Testsuo Watari, Shinya Ogasawara, Teruo Saito1), Yoshinori Tatematsu1),
Sadayoshi Murakami2), Hiroyuki Yamaguchi2) and LHD experiment group西浦 正樹，久保 伸，田中 謙治，關 良輔，下妻 隆，武藤 敬，川端 一男，渡利 徹夫，
小笠原 慎弥，斉藤 輝雄1)，立松 芳典1)，村上 定義2)，山口 裕之2)，LHD実験グループ
National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan1
FIR FU, University of Fukui, 3-9-1 Bunkyo, Fukui, 910-8507, Japan2
Department of Nuclear Engineering, Kyoto University, Kyoto 606-8501, Japan
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
福井大学遠赤外領域開発研究センター 〒910-8507 福井市文京3-9-1
京都大学 〒606-8501 京都市左京区吉田本町
The collective Thomson scattering (CTS) technique has been utilized with the backscattering configuration
to diagnose the bulk and fast ions in the Large Helical Device (LHD). The spectrogram of the scatteredradiation presents the transient phenomena in auxiliary neutral beam heated plasmas. In low temperatureplasma (Te, Ti < 1 keV), a wave excitation is observed in a narrow frequency band. The observed peaks inthe CTS spectrum exist between 0.5 and 1.0 GHz in both frequency sides asymmetry.

1. Introduction
It is essential to understand the behavior ofcharged fusion products in burning plasmas. For
diagnosing them in the plasma core region, one ofchoices is to employ an electromagnetic wave andtheir scattering. The collective Thomson
scattering (CTS) technique has been developed
using a high power and hundred GHz gyrotron infusion devices such as JET, W7-AS, TEXTOR,
and ASDEX Upgrade [1-5]. These results havebeen reported for understanding fast ion related
physics. Moreover, the CTS diagnostic has been
designed for ITER [3, 5].
Beam and fusion products driven instabilities
are observed in fusion devices. These fast ions
not only drive the instabilities, but the driven
instabilities, for example Alfven Eigen modes(AEs), fishbone instabilities, ion cyclotron
emissions (ICE), lower hybrid wave (LH)turbulence, influence on the fast ion confinement
and transport. These nonlinear phenomena arevery complex and still need to be studied. TheCTS diagnostic is applicable to study thesephenomena. These instabilities exist in thevarious frequency ranges. Although the frequency
range would be changed by the plasma
parameters and machine parameters, AEs lie
below a few ten to sub MHz, ICE in a few ten
MHz, and LH turbulence in a few GHz,respectively. The interaction between fast ionsand high frequency of more than MHz could bestudied by CTS diagnostic. The experimental
observation of LH excitation by neutral beam
origin fast ions is reported in W7-AS [2]. The LH
wave with ICE harmonics is simultaneouslyobserved with the injection of auxiliary neutralbeams. The mechanism of LH wave excitation is
explained by the double resonance condition
between a LH wave frequency and higher ion
cyclotron harmonics. In LHD, the excited wave inthe frequency range of LH wave is observed withperpendicular neutral beam injection, which has
been reported in previous paper [6].
2. Experimental setup
We have developed a CTS apparatus to measurebulk and fast ions in the Large Helical Device(LHD) [6-9]. The spectra of the scattered radiationfrom the probing beam are obtained by the broadband receiver resolving the scattered signal into 32channels.
The probing beam from a 77 GHz gyrotron ismodulated with 50 Hz to subtract the backgroundelectron cyclotron emission (ECE) from thedetected signals, and it is injected into plasmas. Fig.
1 shows the CTS spectrogram and the CTS spectra
at specific times. The angle of ∠(k, B)=100.4
degrees is sensitive along to k. The deviation fromthe perpendicular direction is about 10 degrees.
When the NB4 with the energy of ~ 40 keV isinjected, the spectrogram of the scattered radiation
presents the transient changes in the shape with
auxiliary perpendicular neutral beam heatedplasmas. Especially in low temperature plasmas (Te,Ti < 1 keV), a wave excitation is also observed in anarrow frequency band between 0.5 and 1.0 GHz,and at both upper and lower frequency sides
asymmetrically. These peaks are considered to bedue to an excitation of perpendicular-fast-ion drivenwaves such as lower hybrid waves and theirparametric interaction with the injected probe wave.
The wave frequencies are slightly lower than thoseof the lower hybrid waves. A similar phenomenon
has been observed at W7-AS [2].
For the fast ion measurement, the response in thespectrum for fast ions is discussed in the frequency
of more than 1 GHz. The GNET code [10] and thenewly developed OFMC code [11] show the fastion density is of the order of 1017m-3, which is twoorders of magnitude lower than the bulk ion density.
As for measured CTS spectra, the ratio of bulk tofast ion densities should be two orders of magnitudedifference, even though the measured CTS
NB2
NB3

4.5

5.0

Frequency (GHz)
0.0
0.5

1.0

NB4

5.5

6.0

5.5

6.0

-1.0

-0.5

Notch filter

4.5

5.0
Time (s)4.593 s3eV m ]

1000

Ps / ne [10-191005.992 s

104.513 s

1-2-1

0

12

Frequency [GHz]Fig. 3. Measured CTS spectrogram with neutralbeam injections. The lower graph shows the CTS
spectra at different NB injection timing for (1)t=4.513s, (2) t=4.593s, and (3) t=5.992s. The beamenergies are ~170keV for NB1 to 3, and ~40 keV
for NB4.

spectrum in more than 1GHz includes large errors.
Therefore we have to increase the signal to noise
ratio for more effective fast ion detection.
3. Summary
We have developed a collective Thomson
scattering diagnostic system in LHD. The CTS
spectrum has been measured, and then the CTS
spectrum spread is observed during NB injection.
During periodic perpendicular NB injections, sharp
peaks in LH wave range appeared in CTS spectrum.
However, these peaks disappeared with parallel NB
injection. This feature is similar to the observationof LH turbulence at W7-AS.
Acknowledgments
This work is supported by Grant-in-Aid for
Scientific Research(B)#21360455.
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