23P026-P
Dependence of the ICRF Heating Efficiency on the Resonance Position inHeliotron J
ヘリオトロンJにおけるICRF加熱の共鳴位置による加熱特性の変化
Hiroyuki Okada, Hiroto Watada1, Yoshinobu Wada1, Shinji Kobayashi,Hyunyong Lee1, Tohru Mizuuchi, Kazunobu Nagasaki, Takashi Minami, Satoshi Yamamoto,Shinsuke Ohshima2, Takashi Mutoh3, Shigeru Konoshima, Kiyofumi Mukai2, Ling Zhan2,
Hiroaki Yashiro1, Takayuki Minami1, Tasuku Kagawa1, Shohei Arai1, Koji Mizuno1 andFumimichi SANO1
岡田浩之, 和多田泰士 , 和田善信1, 小林進二, 李炫庸1, 水内亨, 長崎百伸, 南貴司,山本聡, 大島慎介2, 武藤敬3, 木島滋, 向井清史1, 臧臨閣1, 八代浩彰1, 南貴之1, 香川輔1,荒井翔平1, 水野浩志1, 佐野史道
Institute of Advanced Energy, Kyoto University, Gokasho, Uji 611-0011, Japan
Graduate School of Energy Science, Kyoto University, Gokasho, Uji 611-0011, Japan
2
Kyoto University Pioneering Research Unit for Next Generation, Gokasho, Uji 611-0011, Japan
3
National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan京都大学エネルギー理工学研究所 〒611-0011 宇治市五ヶ庄
1
京都大学エネルギー科学研究科 〒611-0011 宇治市五ヶ庄
2
京都大学次世代開発ユニット 〒611-0011 宇治市五ヶ庄
3
核融合科学研究所 〒509-5292 土岐市下石町 322-6
1In Heliotron J, the ICRF minority heating has been performed for the investigation of the fast ion
confinement and bulk ion heating. In the standard configuration, the fast minority ion was increased andthe bulk ion temperature was decreased in the on-axis heating comperaring with inner-side heating case.
This is not consistent with the scheme of the minority heating. The Monte-Carlo simulation is performedfor the fast minority ions. The number of fast ions in the inner-side heating is larger in the relatively low
energy region comparing with the on-axis heating case. The higher ion temperature is possibly caused fromthis condition.

1. Introduction
Fast ion confinement is a critical issue for helicaldevices, since magnetic field ripple is ordinarily
large. In Heliotron J, a low-shear helical-axis
heliotron (R0 = 1.2 m, a = 0.1-0.2 m, B0 ≤ 1.5 T)[1, 2, 3]. Fast ion velocity distribution in the low
density region has been investigated using fast
protons generated by ICRF minority heating in
Heliotron J with special emphasis on the effect of
the toroidal ripple of magnetic field strength andheating position. The fast ions are measured by acharge-exchange neutral particle energy analyzer(CX-NPA) installed at the opposite position in thetoroidal angle to the ICRF antennas as shown in Fig.
1 (a). From the measurement, the pitch angle
dependence of the energy spectra for three bumpy
configurations and the heating position dependence
by changing rf frequency were reported [4, 5]. The
high bumpiness was preferable for the fast ion
confinement as expected. In medium bumpiness,
the two conditions of cyclotron resonance layerlocation were performed. The positions of theresonance layers are shown in Fig.1 (b). The

effective temperature of the minority proton inon-axis heating was higher than in the inner-side
Helical Coil(a)(ｂ)

NBI BL-2
ICRF
PlasmaECH−φCX-NPA

0+φNBI BL-1

Toroidal
Coil B

Toroidal
Coil AFig. 1. (a) The arrangement of the heating systems
and the CX-NPA. The horizontal angle of theCX-NPA is also illustrated. (b) The two positions ofthe fundamental resonance layer for minority protons
in the ICRF antenna cross section. Red and blue lines
indicate the on-axis heating case and inner-side
heating, respectively.

heating; however, the bulk deuteron temperature
was lower. It is not consistent with the minority
heating scheme since most rf input power isabsorbed by minority ions. In this report, the energy

spectra in the function of pitch angle in theCX-NPA measurement and the Monte-Carlosimulation results will be discussed.
2. Energy Spectra of Generated Fast Ions andthe Results of the Monte-Carlo Simulation
The rf frequency of 19 MHz is used for theon-axis heating and 23.2 MHz is for the inner-sideoff-axis heating. Target plasmas are generated by a70-GHz ECH with about 300 kW of the injection
power. An ICRF pulse is superposed during an ECHpulse. The ICRF power is about 280 kW andminority ratio is 0.1. Figure 2 (a) and (b) show thehydrogen energy spectra for the on-axis case andthe inner-side case, respectively. In each figure,pitch angle dependence of the energy spectrum isindicated. The observed pitch angle is changed byH spectra2010(a)191018101018101017161016

1510151010(b)1917101014

H spectra

1020
107.45 deg.
112.2 deg.
116.71 deg.
120.9 deg.
124.7 deg.
127.98 deg.

112.20 deg.
116.71 deg.
118.15 deg.
120.90 deg.
122.22 deg.
123.48 deg.
124.69 deg.
125.85 deg.
127.98 deg.

140510energy (keV)

15100510energy (keV)

15Fig. 2 Energy spectra measured by the CX-NPA in thefunction of pitch angle; (a) for the on-axis heating and(b) for high field side heating.

varying the toroidal angle, φ of the CX-NPA
illustrated in Fig. 1 (a), keeping the condition thatthe line of sight crosses the plasma center. In thehigher energy region more than 5 keV, the hydrogen
flux in the on-axis heating case is larger than in theinner-side heating case for the wide range of pitch
angle. The slope of the energy spectrum is steeper
in the inner-side heating case than in the on-axis
heating case even for the low energy portion.
To interpret the experimental results and to
determine the fast-ion distribution in a plasma
volume, Monte-Carlo simulations were performed.
The numerical model includes orbit tracing,
Coulomb collisions, and acceleration by ICRF
heating. Minority protons are used as test particles
and heating is simulated by the velocity kick in theperpendicular direction in velocity space when ionscross the cyclotron layer. In this calculation, theacceleration term for ICRF heating is proportional
to the ICRF electric field amplitude, which is an
input parameter. The electric field amplitude isdetermined from the input power for ICRF heating.
The plasma parameters are Te(0) = 0.7 keV, Ti(0) =0.3 keV, ne(0) = 0.5 × 1019 m-3, and Zeff = 3.0. The

input rf field is adjusted so that the input power isabout 100 kW in each case.
The energy spectra for the on-axis heating caseare shown in Fig. 3 (a) and for the inner-side(b)

(a)
1000

1000

1000

1000

100

100

100

100

10101010111170150
130110234590

670

750

830
910111170
150
130110234590

670

750

830
910Fig. 3 The energy spectra in the function of pitch
angle calculated using the Monte-Carlo code; (a) for
the on-axis heating and (b) for high field side heating.

heating, in Fig. 3 (b). The difference of two cases is
not so clear since the calculated energy range is not
so large, neither. The minority ions at 3 keV in Fig
3 (b) is larger than that in Fig 3 (a). The minority
ions are rapidly decreased above 3 keV in energy
near 90° in pitch angle. This decrease is likely
caused by the increase of loss region in velocity
space because of the power absorption in the outerarea in the plasma minor radius. The number ofions in the low energy is larger for the case of (b)than that for (a). It is possible that the ratio of theabsorbed energy in ions to that in electron is larger
in the case of (b). This is one candidate for thereason that the bulk ion temperature decreased
instead of the increase of fast minority ions whereas
the increase of the bulk ion temperature is caused
mainly by the Coulomb collision between fastminority ions and bulk ions. The larger energy
range simulation is under progress for further
discussion.
Acknowledgments
This work is performed with the support andunder the auspices of the Collaboration Program ofthe Laboratory for Complex Energy Processes,Institute of Advanced Energy, Kyoto University, theNational Institute for Fusion Science (NIFS)
CollaborativeResearchProgram(NIFS04KUHL030 and NIFS04KUHL041), andJSPS KAKENHI 22560819.
.
References[1] H. Sano, et al.,, J. Plasma and Fusion Res. SERIES 3(2000) 26.
[2] T. Obiki, et al., Nucl. Fusion 41 (2001) 833.
[3] M. Wakatani, et al., Nucl. Fusion 40 (2000) 569.
[4] H. Okada, et al., Nucl. Fusion 47 (2007) 1346.
[5] H. Okada, et al., Proc. 17th International Stellarator/Heliotron Workshop, Princeton, 2009, P03-18.