23D11
Effect of energetic-particle induced n=0 instabilities to bulk-ions on LHD
LHDにおける高速イオン励起されたn=0モードとそのバルクイオンに対する影響
M. Osakabe1, T.Itoh1, K. Ogawa3,4, M. Isobe1,2, K. Toi1,3, T.Ido1,3, A. Shimizu1, S. Kubo1,3,K.Nagaoka1, Y.Takeiri1,2 and LHD experiment group長壁正樹1, 伊藤隆文1，小川国大3,4，磯部光孝1,2，東井和夫1,3，井戸毅1,3，清水昭博1，
久保 伸1,3，永岡賢一1，竹入康彦1,2，及びＬＨＤ実験グループ
1

National Institute for Fusion Science, 322-6 Oroshi, Toki 509-5292, Japan
Department of Fusion Science, The Graduate University for Advanced Studies, 322-6 Oroshi, Toki 509-5292, Japan
3
Dept. of Energy Science and Engineering, Nagoya University
4JSPS Research Fellow
1
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
2
総合大・物理 〒509-5292 岐阜県土岐市下石町322-6
3名古屋大学・エネ理工 〒464-8601 名古屋市千種区不老町
4
学振特別研究員

2A bursting up-chirping instability which associates an enhancement of low energy neutral particle flux,
is observed for low density plasmas (ne(0)<1.0x1018[m-3]) on LHD with the Bt=-1.5T and Rax=3.75m
configuration. This mode is only observed when the Electron Cyclotron resonance Heating (ECH) isintensively applied to LHD plasmas and the energetic particles are produced by tangentially injected
Neutral Beam (NB), simultaneously. The toroidal mode number of the instability is identified to bezero, while the poloidal mode number is two, i.e., n=0/m=1. The ion temperature behavior with themode-activity indicates either the existence of additional ion-heating or enhanced radial-transport ofbulk ions by the mode activity.

1. Introduction
Excitationofenergetic-particle
inducedinstabilities is the one of the great concerns on themagnetically confined fusion devices since it might
degrade the confinement of fusion-born energeticalpha particles and might damage the first wall of thevacuum chamber with the loss of theenergtic-particles.
The excitation of Alfvenic Eigen mode byenergetic particles and its influence on the energetic
particle confinement are extensively studied in thepast decade and several reviews can be found on thisissue [1,2]. On the other hand, the excitation of
Geodesic Acoustic Mode (GAM) by energetic
particles are observed and reported recently in severalmagnetically confined plasma devices, such as JET[3],DIIID[4,5] and LHD[6]. This mode becomes more
attractive since the mode might enhance the efficiency
of ion heating by alpha-particles through thechanneling effect [7,8].
On LHD, excitation of the GAM by energetic
particles were already reported in [6]. In thismanuscript, we will report a energetic particle induced
n=0 instability which associates an enhancement of

low energy neutral particle flux.

2. Experimental observations
In Fig.1, a typical discharge wave forms areshown. As shown here, an enhancement of low
energy neutral particle flux is observed with thebursting mode activities. This mode is observed forlow density plasmas (ne(0)<1.0x1018[m-3]) on LHD
with the Bt=1.375~1.5T and Rax=3.75m configuration.
It is only observed when the Electron Cyclotron
resonance Heating (ECH) is intensively applied toLHD plasmas and the energetic particles are producedby tangentially injected Neutral Beam (NB),
simultaneously. The toroidal mode number of theinstability is identified to be zero, while the poloidal
mode number is two, i.e., n=0/m=1. The initialfrequencies of the modes are ranging from 40 to
100kHz. The chirping-up of the mode frequencies isclearly observed, while the chirping down are not.
Since this type of up-chirping and bursting
instabilities was never observed without tangential NB
injection, the mode is considered to be driven byenergetic particles.. The amounts of neutral flux
increase are changing with the mode amplitudes andthe energy ranges of the influenced particles are also
expanded as the increase of the mode amplitudes.
In Fig.2, a typical variation of neutral energy

Neutral flux [a.u.]

10 23
10 22

Δt=2.5ms
1.79128s
1.79378s
1.79628sa)

10 21
10 20
10 19
10 18
0.0

2.0

4.0
6.0Energy[keV]

8.0

10.0

200

10 -1

150

10 -2100

10 -350

10 -4b)0Ti[keV]

2.00
1.50

10 -5

Peak Amplitude [a.u.]Frequency [kHz]spectra, which are measured by tangential Neutralc)

1.00
0.50

Ti-fit0.00

NeutralFlux [a.u.]

10231022

Particle Analyzer, during a mode activity is shownwith temporal behavior of the mode amplitudes andfrequencies. The ion temperatures being evaluatedfrom the slope of the spectra are also shown.
As shown in the figure, the mode glows quickly
at its initial phase. When the mode amplitude
reaches a certain level (~2x10-2), the ion
temperature starts to increase and the effective
growth rate of the mode decreases,simultaneously.
This behavior indicateseither the additional ion-heating or enhanced
radial transport of bulk-ions by the mode
activities.
In the presentation, detailed
analysis on this phenomenon will be presented

Acknowledgments
This work is supported by NIFS11ULRR006
and NIFS11ULRR010.

References[1] A.Fasoli, et.al., Nucl. Fusion 47 (2007) S264
[2] W.W.Heidbrink, Physics of Plasmas 15 (2008)055501[3] H. L.Berk, et.al., Nucl. Fusion 46 (2006) S888

1.1keV
2.2keV
3.9keV

5.1keV
7.6keV

1021
1020
1019
1018
1017
1.790

Fig.1 Magnetic-probe (Mirnov-coil) signal signal(top), Contour plot for the spectrogram ofmagnetic probe(middle) and that for neutral flux
spectra(bottom) are shown.

d)

1.795

1.800
time[sec]

1.805

1.810

Fig.2 Change of (a)neutral energy
spectra , (b) mode amplitude(blue) andfrequency(red), (c)ion-temperature and(d) temporal behavior of neutral flux
during the mode activity are shown[4] R.Nazikian, et.al., Phys. Rev. Lett. 101(2008)185001[5] G.Y.Fu, Phys. Rev. Lett. 101(2008)185002[6] T.Ido, et.al, Plasma Phys. and Control. Fusion 52(2010) 124025[7] N. J. Fisch and M. C. Herrmann: Nucl. Fusion 34(1994) 1541.
[8] M. Sasaki, K. Itoh and S. Itoh: Plasma Phys. andControl. Fusion 53 (2011) 085017.