25C09
Radial plasma measurements by using multipoint measuring YAG-Thomson
scattering system in the tandem mirror GAMMA 10
タンデムミラーGAMMA 10におけるYAG-Thomson散乱計測システムの空間多点計測による径方向プラズマ計測
Masayuki Yoshikawa1, Masato Morimoto1, Yoriko Shima1, Junko Kohagura1, Mizuki Sakamoto1,Yousuke Nakashima1, Makoto Ichimura1, Tsuyoshi Imai1, Kazuo Kawahata2, Ichihiro Yamada2,
Hisamichi Funaba2, Ryo Yasuhara2, and Takashi Minami3
吉川正志1, 森本真人1，嶋 頼子1，小波蔵純子1，坂本瑞樹1，中嶋洋輔1，市村 真1，今井 剛1，川端一男2，山田一博2，
舟場久芳2，安原亮2，南貴司3
1Plasma Research Center, University of Tsukuba, 1-1-1 Tennodai, Tsukuba-city, Ibaraki 305-8577, Japan
2
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki-city, Gifu 509-5292, Japan
3
Institute of Advanced Energy, Kyoto University, Gokasho, Uji-city, Kyoto 611-0011, Japan1
筑波大学プラズマ研究センター 〒305-8577 茨城県つくば市天王台1-1-1
2
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
3京都大学エネルギー理工学研究所 〒611-0011 京都府宇治市五ケ庄

A yttrium-aluminum-garnet (YAG) Thomson scattering (TS) system was constructed and applied to thetandem mirror GAMMA 10 device to measure the electron temperature and density. A large solid-angle TS
light-collection system was achieved by use of a spherical mirror system and large numerical aperture ofbundled optical fiber. We prepared five channel optical fiber bundle and two five-channel polychromatorswith avalanche silicon photo diodes for multipoint measurements. The electron temperature increases from0.04 keV to 0.08 keV was observed in the hot ion mode plasma with application of electron cyclotron
heating in the plug/barrier cells

1. Introduction
Thomson scattering (TS) is the most importantdiagnostic to measure the electron temperature andelectron density in fusion devices [1-4] and also in
GAMMA 10 device [5]. GAMMA 10 is aneffectively axisymmetrized minimum-B anchoredtandem mirror with thermal barrier at both
end-mirrors [5]. The plug/barrier cells are located atboth ends of GAMMA 10, where the electron
confinement potentials and ion confinement
potentials are produced by the application of plugand barrier electron cyclotron resonant heating(B/P-ECH). The plasma is created by plasma guns,and heated and sustained using ion cyclotron rangeof frequency heating (ICH) systems. The typicalelectron density, electron and ion temperatures areabout 2  1018 m-3, 0.1 keV and 5 keV, respectively,
during application of P/B-ECH. We planned toinstall the neodymium-doped yttrium aluminium
garnet (Nd:YAG) laser TS system in order tomeasure electron temperature directly in the central
cell of GAMMA 10. The YAG-TS system isnormally used in the higher electron density
plasmas, over 1019 m-3. Then, an efficient TS system
is necessary to apply to measure low density

plasmas in the region of less than 1019 m-3, such as
the GAMMA 10 plasma and the peripheral plasmaof high density fusion plasmas. In this report, weshow the newly installed YAG-TS system and thefirst results of radial electron temperature
measurements in the tandem mirror GAMMA 10.
2. YAG-TS system
The YAG-TS system is constructed with the laser,
the incident optics, the light collection optics, thesignal detection electronics, and the data recording
system. A 10 Hz Nd:YAG laser (Continuum,Powerlite 9010) with an energy per pulse of 2 J anda pulse width of about 10 ns, operating at thefundamental wavelength of 1064 nm is used. Thelaser beam diameter at the plasma center is about 1mm with a focusing lens of f = 2 m. For the lightcollection optics, we used the spherical mirror with
Al:SiO2 coated, curvature radius of 1.2 m anddiameter of 0.6 m. The scattered light is collectedby the spherical mirror, reflected and reaches abundled optical fiber with cross-section of 2×7mm. The magnification of the collection optics is2.2. The length of scattering volume along the laser
is 15.4 mm and scattering angle is 90◦. A solid angle

-3Electron temperature [ x 10 keV ]of 0.078 sr can be realized of the light collection
optics. The each channel of 6.67 m long 5-channel
bundled optical fiber (Mitsubishi Densen,FS10-43001, NA:0.47) is connected to the5-channel pohychlomator. The YAG-TS systeminstalled in GAMMA 10 central cell is shown in Fig.
1. The polychromator is composed with five relay
Fig. 2. Diamagnetismand line density.

Fig. 1. GAMMA 10 Thomson scattering system.

and collection lenses, five interference filters, andfive silicon avalanche photodiodes (APD)(PerkinElmer, C30950E). We prepared a newpolychromator with new APD (Hamamatsu,C8890-30) for multi-point measurement. A
four-channel high speed oscilloscope (Tektoronix,DPO4034B) was used to measure four wavelength
channels simultaneously with bandwidth of 350
MHz and sampling rate of 2.5 GS/s. The measured
signals are recorded by the Windows PC withLabVIEW analyzing software.
The Raman and Rayleigh calibration experiments
were carried out for setting of optical system andstray light in the evaluation of GAMMA 10
YAG-TS system. The measured scattering signals
are proportional to the gas pressure. The stray lightin this system is very small.
3. Electron temperature measurement
We applied the YAG-TS system to measure theelectron temperature of GAMMA 10 plasma. The
plasma is produced from t = 50 to 240 ms withheated by the ICH from t = 51 to t = 240 ms and theconfinement potential by applying B-ECH withpower of 150 kW from t = 150 to 200 ms andP-ECH with power of 200 kW from t = 151 to 181
ms, respectively. Figure 2 shows the temporal
evolutions of diamagnetism (dotted red line) andelectron line density (solid blue line). We measure
the electron temperatures at t = 140.1 ms and t =170.1 ms, by changing the YAG laser injection time.
The output signal of each channel is integrated in t= 40 ns which covers the TS pulse. The backgroundplasma radiation is negligible in GAMMA 10. We
used the minimizing the chi-squared value to obtain
the electron temperature. The signal to noise ratio is120

w/o ECH
with ECH

1008060
40200-20 -15 -10 -5 0 5
X [ cm ]Fig.
3.
temperature
profile.

10 15 20Electronradial

about 3. We can obtain the electron temperatureof about 0.04 keV before applying P/B-ECH. Withapplication of P/B-ECH, the electron temperature
increased to about 0.08 keV. We changed themeasuring position of electron temperature bychanging the bundled optical fiber position
shot-by-shot. Figure 3 shows the radial electron
temperature in GAMMA 10. In Fig. 3, closed red
circles and closed blue squares show the electron
temperature radial profiles without P/B-ECH andthose with P/B-ECH, respectively. The temperature
peeking at the plasma center is observed byapplying P/B-ECH. Unfortunately, at this time wecould not show the multi-point measurement results.
Anyway, we can measure the electron temperaturein the very low plasma density region less than 1×1018 m-3.
4. Summary
YAG-TS system was newly installed in thetandem mirror GAMMA 10. This system can beoperated to measure electron temperature in thevery low plasma density region less than 1×1018
m-3. We can successfully measure the radial
electron temperature in the tandem mirror
GAMMA 10 by using YAG-TS system for the firsttime. The radial electron temperature distribution isobtained at one position and one period during theplasma duration at this time. We have constructed
the two-point measuring system. Then we willobtain the multipoint Thomson scattering signals in
the next experimental campaign.
References[1] K. Narihara et al., Fusion Eng. Design 34-35, 67(1997).
[2] K. Narihara, I. Yamada, H. Hayashi, and K.
Yamauchi, Rev.Sci. Instrum. 72, 1122 (2001).
[3] S. Kainaga, et al., Plasma Fusion Res. 3, 027 (2008).
[4] H. G. Lee, et al., Rev. Sci. Instrum. 72, 1118 (2001).
[5] M. Yoshikawa, et al., Plasma Fusion Re. 6, 1202095(2010).