23P090-P
Interactions of High-Energy Ions with High and Low Frequency Fluctuationsin the GAMMA 10 Tandem Mirror
GAMMA 10における高エネルギーイオンの高周波および低周波揺動との相互作用
Makoto Ichimura, Mafumi Hirata, Ryuya Ikezoe, Toru Iwai, Takuro Yokoyama, Yumeto Ugajin,Tatsunori Sato, Takuma IImura, Yu-ki Saito, Tsuyoshi Imai
市村 真、平田真史、池添竜也、岩井透、横山拓郎、宇賀神ゆめと、佐藤達典、飯村拓真、斎藤裕希、今井剛
Plasma Research Center, University of Tsukuba
1-1-1, Tennoudai, Tsukuba, Ibarak 305-8577, Japan筑波大学プラズマ研究センター 〒305-8577 つくば市天王台1-1-1
In the ion cyclotron range of frequency (ICRF) heating experiments on GAMMA 10, wave-wave andwave-particle interactions are investigated. Fluctuations of which frequencies are lower than 100 kHz havebeen observed in a typical discharge. These low-frequency modes are detected in the signal of electrostatic
probes in the central cell and in both signals of high-energy ion detectors in the central cell and at the eastend. Radial transport of high-energy ions owing to drift-type and flute-type fluctuations has been observedin the central cell. Axial transport of high-energy ions owing to the Alfvén-ion-cyclotron (AIC) modes isclearly indicated. The fluctuations, of which frequencies are the differential frequency between eachdiscrete peak of the AIC modes, are observed in the signal of the end-loss high-energy ion detector.

1. Introduction
Ion cyclotron range of frequency (ICRF) wave is
one of most promising schemes for heating fusion
plasmas. When the ICRF power and consequent
wave energy levels increase, it will become
important to understand the detailed physics ofwave-wave and wave-particle interactions. It isrequired to consider both linear and nonlinear
processes for deposition of ICRF powers, forexample, the parametric decay of the heating ICRF
waves has been observed in many fusion
experiments. Axial and radial transports ofhigh-energy ions owing to these waves are studied
in this research.
In the GAMMA 10 tandem mirror, ICRF waves
have been used for the plasma production, heatingand sustaining MHD stability. In a high power
ICRF heating experiment, plasmas with strong
temperature anisotropy have been formed because
the fundamental cyclotron resonance layer exists
near the midplane of the central cell.
Alfvén-ion-cyclotron(AIC)
modes
arespontaneously excited due to the strong temperature
anisotropy. The AIC modes have several discrete
peaks in the frequency spectrum just below the ion
cyclotron frequency. Fluctuations of which
frequencies are the differential frequency between
each discrete peak of the AIC modes are observed.
Radial transport of high-energy ions owing to
low-frequency drift-type and flute-type fluctuations

has been observed in the central cell.[1]2. Experimental Setup
For the initial plasma production, an ICRF
source (RF1) with so-called Nagoya Type-III
antennas on both east and west sides of the central
cell is used in combination with the hydrogen gas
puffing. Fast Alfvén waves are excited in the central
cell and propagate to the anchor cell. The MHD
stability of GAMMA 10 is kept by the anchor
plasma with averaged minimum-B configuration.
Another ICRF source (RF2) with conventional
double half-turn (DHT) antennas installed on bothsides of type III antenna is applied for the main ion
heating in the central cell.
The typical plasma parameters are the density of2 x 1018 m-3, the ion temperature of more than 5 keVand the temperature anisotropy of more than 10.
The temperature anisotropy is estimated fromsignals of the diamagnetic loop arrayed in theaxial direction. Magnetic fluctuations excited in
the plasma are detected by using magnetic probearray both in the axial and azimuthal directions anda microwave reflectometer. [2]To measure the behavior of high-energy ions,diagnostic tools with a semiconductor detector areinstalled at the midplane of the central cell (centralcell High-Energy-ion Detector; ccHED) and theeast end cell (east end HED; eeHED). The ccHED
is inserted perpendicularly to the magnetic field line

4. Summary
Wave-particle interactions observed in GAMMA
10 are described. The first is the pitch angle

Diamag. Signal
Line Density
Hot-Ion-4
17 -2
Signal [a.u.] Anisotropy[10 Wb][10 m ]

3. Experimental Results
The ICRF waves have been used for the plasma
production and heating in the GAMMA 10 tandem
mirror. Figure 1 shows the temporal evolution of (a)line density and (b) three diamagnetic signals atdifferent locations along the magnetic field line. As
shown in the figure, there are large differences
between diamagnetic signals near the midplane (z =-0.33 m) and off-midplane (z = 1.5 m and z = 1.9m).
These differences indicate the pressure
anisotropy as shown in Fig.1(c). Plasmas withstrong pressure anisotropy of more than 10 areformed in the central cell. The AIC modes areexcited spontaneously due to such strong pressure
anisotropy. ccHED and eeHED are used for theevaluation of the transport of high-energy ionsowing to fluctuations in the perpendicular and along
the magnetic field line, respectively. The raw
signal of eeHED is shown in Fig.1(d). When thediamagnetic signal near the midplane increases andthe temperature anisotropy becomes high, theeeHED signal increases suddenly. Fluctuations arecontained in the eeHED signal as shown in thefigure. The frequency spectrum of the eeHED
signal is analyzed as shown in Fig.1(e).
Fluctuations around 100 kHz, of which frequencies
are differential frequencies between discrete peaksof the AIC-modes, are clearly observed. Thesefluctuations are also detected in the signal ofmagnetic probes installed on the central cell.
On the other hand, radial transport of high-energy
ions owing to low-frequency drift-type andflute-type fluctuations has been observed in thecentral cell. ccHED is located just outside of thelimiter radius at the central cell midplane and can
detect high-energy ions which escape from theconfined region near their turning points in theperpendicular direction.[1]The pitch angle scattering owing to thespontaneously excited Alfvén waves and the radialtransport owing to low-frequency drift-type andflute-type fluctuations are clearly detected
experimentally.

5(a)010 (b)z = -0.33 m
5z= 1.5 m

020 (c)z = 1.9 m

1002 (d)10100

Frequency [kHz]and is positioned just outside of the limiter radius in
the midplane of the central cell. By rotating ccHED
against to the normal axis of the magnetic field line,
a pitch angle profile of high-energy ions can bemeasured. The eeHED can measure high energy
ions escaping along the magnetic field line from thecore region of the central cell.

(e)

50050

100

150200Time [ms]250

Fig.1 Temporal evolution of (a) line density, (b)diamagnetic signals at z=-0.33 m, 1.5 m and 1.9m, (c) estimated pressure anisotropy, (d) raw
signal of eeHED and (e) an intensity plot of
the frequency spectrum of the eeHED signal.

scattering of high-energy ions owing to thefluctuations of which frequencies are differential
frequencies between discrete peaks of the AICmodes. The second is the radial transport ofhigh-energy ions owing to drift-type and flute typefluctuations near their turning points in theconfining mirror field.
Acknowledgments
This work is partly supported by Grant-in-Aidfor Scientific Research under the Ministry ofEducation, Culture, Sports, Science and Technology,
Japan (No.21540506) and also partly supported by
the bidirectional collaborative research program ofNational Institute for Fusion Science, Japan(NIFS09KUGM040).
References[1] M. Ichimura, et al., Fusion Science and Technology,
59, No.1T (2011) 98-103.
[2] R. Ikezoe, et al, Plasma Fusion Res. 6, 2402047(2011).