23P030-P
Density modulation experiment in Heliotron-J ECH plasma
ヘリオトロンJにおけるECHプラズマでの密度変調実験
Kiyofumi Mukai1, Kazunobu Nagasaki2, Tohru Mizuuchi2, Vladimir Zhuravlev3, Kenji Tanaka4,Takashi Minami2, Hiroyuki Okada2, Shinji Kobayashi2, Satoshi Yamamoto2, Yuji Nakamura1,Kiyoshi Hanatani2, Shinsuke Ohshima5, Koji Mizuno1, Hyunyong Lee1, Linge Zang1,Shohei Arai1, Tasuku Kagawa1, Takayuki Minami1, Hiroaki Yashiro1, Hiroto Watada1,Yoshinobu Wada1, Shigeru Konoshima2, Fumimichi Sano2
向井清史1，長崎百伸2，水内亨2，V. Zhuravlev3，田中謙治4，南貴司2，岡田浩之2，小林進二2，山本聡2，中村祐司1，花谷清2，大島慎介5，水野浩志1，H.Y. Lee1，L. Zang1，荒井翔平1，香川輔1，南貴之1，八代浩彰1，和多田泰士1，和田善信1，木島滋2，佐野史道2
1

Graduate School of Energy Science, Kyoto University, Gokasho, Uji, 611-0011, Japan京都大学エネルギー科学研究科 〒611-0011 京都府宇治市五ヶ庄
2Institute of Advanced Energy, Kyoto University, Gokasho, Uji, 611-0011, Japan京都大学エネルギー理工学研究所 〒611-0011 京都府宇治市五ヶ庄
3
RRC “Kurchatov Institute”, Institute of Nuclear Fusion, Moscow, 123182, Russia
クルチャトフ研究所
4
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
核融合科学研究所 〒509-5292 岐阜県土岐市下石町 322-6
5Pioneering Research Unit for Next Generation, Kyoto University, Gokasho, Uji, 611-0011, Japan
京都大学次世代開拓ユニット 〒611-0011 京都府宇治市五ヶ庄

Density modulation experiments by using gas puff fuelling have been carried out in Heliotron-J ECH plasmas toevaluate the diffusion coefficient Dcore and convection velocity Vcore in the core region. Background line averaged
density`ne was fixed around 0.6 or 0.9 ´ 1019 m-3.`ne were modulated with the amplitude of 0.1 ´ 1019 m-3 in 50
Hz. According to the transport analysis, Vcore are positive under both the conditions, and larger in low-density
region. These imply that an outward convective term plays an important role to determine the particle transport
in ECH plasmas, especially in the low-density region.

1. Introduction
Particle transport analysis is one of the important
issues in the magnetically confined plasma research.
The goal of this study is to reveal the feature ofparticle transport in Heliotron-J ECH plasma. Here,density modulation experiments by using gas puff
fuelling have been carried out to evaluate thediffusion coefficient Dcore and the convection
velocity Vcore in the plasma core region. Electron
density profile measurement is required to analyze
particle transport. In this study, ne profile wasmeasured with an amplitude modulation (AM)reflectometer [1, 2]. AM reflectometer is a usefuldiagnostic to measure ne profile and to study
particle transport [3, 4].
2. AM Reflectometer in Heliotron J
The schematic of the reflectometer is as follows:
an AM type system is adopted to mitigate density
fluctuation effects during profile measurement. TheX-mode is selected as the propagation mode inorder to measure even a flat or hollow ne profile
which is typically observed in ECH plasmas ofhelical devices. Such flat and hollow profiles havebeen measured in Heliotron-J ECH plasmas [2].
The carrier frequency of the reflectometer ranges
from 33 GHz to 56 GHz, and can be swept as
triangular wave with the sweeping frequency of 1
kHz for electron density profile measurement. Time
resolution is 1 ms due to data averaging over 2
sweeps. The modulation frequency is 200 MHz.
3. Transport Analysis Method
The particle transport equations can be expressed
as follows:ì¶n e ¶t = -Ñ × Γ + S
íΓ = - DÑn e + n e Vî(1)Here, G is the particle flux. S is the particle sourceand negligible in the region of r £ 0.6 since it isfuelled by gas puffing. It is assumed that themodulated component is described asn~e = A(r ) sin{wt - f (r )}(2)where A and f are the amplitude and phase of themodulated component, w is the modulatedfrequency. Then, D and V can be expressed asfollows [5]:Figure 2 shows the c2 profiles calculated fromthe analysis as described in Sec. 3. The analysis
results in Dcore = 5.2 m2/s and Vcore = 59 m/s in thecase of`ne = 0.6 ´ 1019 m-3. Under the conditionof`ne = 0.9 ´ 1019 m-3, Dcore = 2.3 m2/s, Vcore = 2.3
m/s are obtained. Vcore are positive in bothconditions, and Vcore in the low density case is larger
than that in the high density case. These imply thatan outward convective term plays an important role
to determine the particle transport in ECH plasmas,
especially in the low density region.

ì D = -w (Y sin f + X cos f ){r (¶f ¶r )A}-1
ï(3)í V = -w [{(¶A ¶r )Y - (¶f ¶r )AX }sin f
ï2 -1
î + {(¶f ¶r )AY + (¶A ¶r )X }cos f ] r (¶f ¶r )A{}Here,rr00

X = ò rA cos fdr , Y = ò rA sin fdr(4)

In this study, c2 is determined to estimate thecoefficients in the core region, Dcore and Vcore, as [6][c 2 = å {Aexp cos f exp - Acalc cos f calc }2r+ {Aexp sin f exp - Acalc sin f calc }

2]

(5)

where the suffixes of exp and calc indicate theexperimental and calculated values. The
experimental value is measured with the AM
reflectometer measurement. The calculated value isestimated by using the following model and Eq. (3).
D = Dcore , V = rVcore(a)`ne = 0.6 ´ 1019 m-3(b) `ne = 0.9 ´ 1019 m-3
Fig.1. Time evolutions of`ne, Wp and GP control signal(6)Consequently, the minimum of c2 gives Dcore andVcore.
4. Experimental Results and DiscussionDensity modulation experiments by using gas
puff fuelling have been carried out in Heliotron-J
ECH plasmas. Figure 1 shows the time evolutionsof`ne, Wp and gas puff (GP) control signal. Theplasmas are produced and heated by using an ECH(70 GHz, 0.25 MW). The amount of injection gas
puff fuelling can be controlled by applying voltage
to piezoelectric valves. Considering recycling effect,
the gas puff fuelling was gradually decreased tokeep background`ne constant. Two cases of thebackground`ne were examined around 0.6 or 0.9 ´1019 m-3. Under both conditions,`ne were modulatedwith the amplitude of 0.1 ´ 1019 m-3 in 50 Hz.

(a)`ne = 0.6 ´ 1019 m-3(b) `ne = 0.9 ´ 1019 m-3
2Fig.2. c profiles

Acknowledgments
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 (NIFS10KUHL030).
References[1] K. Mukai et al.: Contrib. Plasma Phys. 50 No. 6-7(2010) 646.
[2] K. Mukai et al.: Plasma Fusion Res. 6 (2011)
1402111.
[3] W. W. Xiao et al.: Phys. Rev. Lett. 104 (2010)
215001.
[4] W. W. Xiao et al.: Rev. Sci. Instrum. 81 (2010)
013506.
[5] H. Takenaga et al.: Plasma Phys. Control. Fusion 40(1998) 183.
[6] K. Tanaka et al., Fusion Sci. and Technol., 58, 70(2010).