23P062-P
The radial profile measurement of electron temperature fluctuation in PANTAPANTAにおける電子温度揺動の径方向分布計測	 
Katsuyuki Kawashima1, Shigeru Inagaki2, 3, Stella Oldenbürger3, Yoshihiko Nagashima2,3,Tatsuya Kobayashi1, Noriko Ohyama1, Yuuki Tobimatsu1, Tetsuo Yamashita1, Soutaro Yamada1,
Hiroyuki Arakawa4, Takuma Yamada3,5, Masatoshi Yagi2,3,6, Naohiro Kasuya3,7, Makoto Sasaki2,3,Akihide Fujisawa2,3, Sanae-I. Itoh2,3 and Kimitaka Itoh3,7
川島勝之１,	 稲垣滋2,3,	 Stella	 Oldenbürger3,	 永島芳彦2,3,	 小林達哉1,	 大山乃里子１,	 飛松
祐紀1,	 山下哲生１,	 山田宗太郎１,	 荒川	 弘之4,	 山田琢磨3,5,	 矢木雅敏2,3,6,	 糟谷直宏3,7,	 佐々木真2,3,	 藤澤彰英2,3,	 伊藤早苗2,3,	 伊藤公孝3,7	 
1Interdisciplinary Graduate School of Engineering Sciences, Kyushu University,
6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan1
九州大学総合理工学府 〒816-8580 福岡県春日市春日公園6-1
2
Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan2
九州大学応用力学研究所 〒816-8580 福岡県春日市春日公園6-1
3Itoh Research Center for Plasma Turbulence, Kyushu University,
6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
3
九州大学伊藤極限プラズマ研究連携センター 〒816-8580 福岡県春日市春日公園6-1
4
Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki 311-0193, Japan4
日本原子力研究開発機構 〒311-0193 茨城県那珂市向山801-1
5Graduate School of Frontier Sciences, The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa, Tokyo 277-8561, Japan5
東京大学新領域創成科学研究科 〒277- 8561 千葉県柏市柏の葉5-1-5
6Japan Atomic Energy Agency, 2-166, Omotedate, Obuchi, Rokkasho-mura, Aomori, 039-3212 Japan6日本原子力研究開発機構 〒039-3212	  青森県六ヶ所村尾駮表舘2番166
7
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan7
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
Electron temperature fluctuations observed by the triple probe method in PANTA. Five Langmuir probes
have been aligned in a straight line and the probe angle has been adjusted along magnetic field line
direction by checking that floating potential fluctuations of all pins have same phase. Radial profiles ofaveraged electron temperature and normalized fluctuation levels were obtained. The electron temperaturefluctuation level was found to be low ( ! 10 %) across the plasma radius.

1. Introduction
Fluctuation measurements are widely carriedout in many magnetically confined plasma
devices to understand the cross-field transport
relevant
toturbulence.
Evaluation
oftime-averaged flux is dependent on fluctuationsof density, poloidal electric field and temperature.
High temporal and spatial resolutions are required
for fluctuation measurements. Langmuir probes
fulfill such high requirement for density andpotential. However the electron temperaturefluctuation measurement with high temporal
resolution is more difficult. The electrontemperature fluctuation is often assumed to besmall and neglected in the evaluation offluctuation-driven transport.
Recently, electron temperature fluctuation wasobtained by improved triple probe method in highdensity helicon plasma where triangle-wave-likefluctuations are excited [1].
In this paper, we evaluate the radial profile ofelectron temperature using an improved triple
probe technique in plasma where fluctuations
with a broad spectrum are excited.
2. Experimental Setup
Fluctuation measurements were carried out inPlasma Assembly for Nonlinear Turbulence
Analysis (PANTA). PANTA is linear magneticplasma confinement device. Cylindrical plasma(length=4 m, diameter=10 cm) was produced with ahelicon wave (7 MHz, 3 kW) using a double-loop
antenna around a quartz tube. The quartz tube isfilled with argon gas. The magnetic field was 0.09

T. The vacuum vessel was at ground potential. An
insulated endplate allowed controlling the potentialof the plate by electrical biasing. Fluctuations weremeasured with movable 5-pins probe. This probe
was installed at z = 1.675 m from the quartz tube.
The five tungsten pins (diameter=0.7 mm, length=3mm) were aligned in a straight line with intervals of
3 mm and the probe was allowed to rotate to follow
the magnetic field line direction. The phase delay offloating potential between the pins was canceled byadjusting the angle of the probe to match themagnetic field line. The time-averaged values ofeach pin’s floating potential were the same within
the error of 6 %. The central two or three pins wereused for the double probe and triple probe
measurements and the other pins were measuring
floating potential.
3. ResultThis experiment was carried out at low neutral
gas pressure under no biasing condition (endplate isgrounded). The fluctuation spectrum has a peakaround 7 kHz and FWHM of peck is broad [2].
Figure 1 shows radial profiles of averaged values.
The averaged values are also measured by double
probe method. Averaged values of electron
temperature estimated by two methods wereconsistent as shown in Fig.1 (b).
Figure 2 shows radial profiles of normalized
fluctuation amplitude. The fluctuation amplitude
was calculated with all frequency components.	 
Electron temperature fluctuation amplitude is
one-third compared to density fluctuation amplitude
at r=4 cm, which is relatively larger than thatobserved in the triangle-wave-like fluctuations inhigh density plasma [1]. Electron temperaturefluctuation levels remain small in the central region,
however density fluctuation levels decrease in thecentral region and thereby the ratio of electron
temperature and density fluctuation levels increase( (T!e Te ) ( N! e N e ) ~0.6).
4. Discussions and Summary
We obtained the radial profile of fluctuationlevels using an improved triple probe technique.
The electron temperature fluctuation level is lower
than fluctuation levels of other quantities, but ratioof amplitude between electron temperature anddensity fluctuation becomes large in the central
region. Thus, electron temperature fluctuation may
not be neglected in the estimation of heat and also
particle fluxes induced by fluctuations in the coreregion.
Endplate biasing experiments have been

performed in PANTA. The change in fluctuations
with respect to biasing will be discussed.

Fig.1. Radial profiles of mean floating potential (a),mean electron temperature (b), mean density (c). The
black line shows result from double probe and the redline shows result from triple probe. The error bar
corresponds to standard deviation for series of threeshots.

Fig. 2. Radial profiles of normalized fluctuations
amplitude. The black line corresponds to normalized
potential fluctuation, the red line to normalized electron
temperature fluctuation and the green line to normalized
density fluctuation. The error bar corresponds to standard
deviation for series of three shots.

Acknowledgments
This work is partly supported by a grant-in-aidfor scientific research from JSPS (21224014,23360414) and by the collaboration programs ofNIFS (NIFS10KOAP023) and of the RIAM ofKyushu University.
References[1] K. Kawashima et al.: Plasma Fusion Res. 6 (2011)2406118.
[2] H. Arakawa et al.: Plasma Fusion Res. 5 (2010)
S2044.