23P094-P
NBI Plasma Startup using Non-resonant Microwave Injection in Heliotron J
ヘリオトロンJにおける非共鳴マイクロ波入射アシストによるNBIプラズマ着火
Kobayashi Shinji1, Nagasaki Kazunobu1, Yamamoto Satoshi1, Sakamoto Kinzo1, Mizuuchi Tohru1,
Okada Hiroyuki1, Minami Takashi1, Hanatani Kiyoshi1, Nakamura Yuji2, Konoshima Shigeru1,
Ohshima Shinsuke3, Mukai Kiyofumi2, Lee Hyunyong2, Zang Linge2, Toushi Kiyoshi1,
Sano Fumimichi1
小林進二1, 長崎百伸1, 坂本欣三1, 山本聡1, 水内亨1, 岡田浩之1, 南貴司1, 花谷清1,中村祐司2, 木島滋1, 大島慎介3, 向井清史2, Lee Hyunyong2, Zang Linge2, 東使潔1, 佐野史道1
1

Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan京都大学エネルギー理工学研究所 〒611-0011 宇治市五ヶ庄
2Graduate School of Energy Science, Gokasho, Uji, Kyoto 611-0011, Japan京都大学エネルギー科学研究科 〒611-0011 宇治市五ヶ庄
3
Kyoto University Pioneering Research Unit, Uji, Kyoto 611-0011, Japan
京都大学次世代研究開拓ユニット 〒611-0011 宇治市五ヶ庄

This paper describes development of a plasma startup method with neutral beam injection by assistance of5kW 2.45GHz microwaves in Heliotron J. The plasma startup has succeeded in the magnetic field strength
more than 0.63T, where a fundamental or higher-harmonic layer for the microwave has not existed in theconfinement region. The microwave power scan experiments show the higher microwave power isdesirable for the reliable density build-up at lower magnetic field strength.

1. Introduction
Electron cyclotron heating (ECH) with either
fundamental O-mode or second harmonic X-mode
is a conventional scheme for plasma productioncommonly utilized in many heliotron devices [1].
While this scheme is advantageous for reliable
startup and sustaining high electron temperatureplasmas, it requires electron cyclotron resonancelayer in the confinement region, giving rise to thelimitation of operational magnetic field regime
satisfying the electron cyclotron (EC) or its higher
harmonic resonance.
Plasma startup only by neutral beam injection(NBI) has been demonstrated in LHD and W7-AS[2,3]. An issue for plasma production only by NBI
is how the electron temperature is increased to ahigh enough value to ionize the background neutralgas. Since the electrons are heated only through theCoulomb collisions with the injected beam ions inthe early phase of the NBI startup plasmas, theconfinement time of the beam ions should be longer
than the production time for the amount of the hotelectrons.
In this paper, we present experimental results on
startup of NBI plasmas by assistance of 2.45GHz
5kW microwaves in Heliotron J [4]. We
experimentally demonstrate that the plasma wasbuilt-up less than 20ms after the turning-on of NBI,
and that the operational magnetic field was widelyextended down to B=0.63T.

2. Experimental results and discussions
Experiments were carried out in the standard
configuration at the magnetic field strength B on
the plasma axis from 0.59T to 1.0T. Figure 1 showsa typical time evolution of plasma parameters in theNBI plasma startup discharge at B=0.83T. The 2.45
GHz microwaves (5kW) were launched 0.6 s before
turning-on of neutral beams. Neither fundamental
nor higher harmonic EC resonance for 2.45GHz
microwaves exists in the vacuum chamber during
the microwave
launching. A plasma with electron_density (ne) less than 11017m-3, ECE intensity andCIII line emission were observed in the ramp-up
phase of a poloidal (AV) coil current. The
third-harmonic resonance layer for the ECE of
75.5GHz frequency is located at r/a = 0.3 in theconfiguration. It should be noted that the ECE
intensity is not proportional to the local electron
temperature because the plasma is optically thin due
to quite low density, but it can be regarded as ameasure of the intensity of “hot” electrons. After
that, increase in the density of the seed plasma wasobserved from t=-120ms. In the case that themicrowave was not launched, on the other hand,increase in the seed plasma density was notobserved and high density plasmas could not bebuilt after the NBI injection.
The co- and counter- NBIs were injected
at the_port through power of 1MW in total. ne increased

OVne

W DIA

0180 200 220 240 260 280 300time (ms)NBILOOPV

AV

OV(x20)6Out ofRange 4
20-303 (f) density
210AV coil current
2 (g)0Loop Voltage-2-300 -200 -100
0100time (ms)17ECEe3 (e) CIII(x10)n (x10 m )ECE, CIII, OVIe17nL-2(V) (x10 m ) (A.U.)

2.45GHz

References[1] K. Nagasaki, et al., Nucl. Fusion 45 (2005) 13-21[2] O. Kaneko, et al., Nucl. Fusion 39 (1999)
1087-1091., O. Kaneko, et al., Nucl. Fusion 42(2002) 441-447.
[3] W. Ott, E. Speth and W7-AS Team, Nucl. Fusion 42(2002) 796-804.
[4] S. Kobayashi, K. Nagasaki et al., Nucl. Fusion 51(2011) 062002.
Low  config. B=0.81Tt2ECE200300

Acknowledgments
This work is performed with the support andunder the auspices of the Collaboration Program ofIFig. 1. Time evolution of plasma parameters obtainedin NBI startup plasmas (standard config.).

Threshold

10.5
00.08
interferometorDensity
P =4.8kW (#41127) Build
2.45
4.0kW (#41128)
3.75kW (#41134)
0.04
0.06

0.02
No Build
3.5kW (#41133)
3.0kW (#41131)

e19-3n (x10 m )016ms averaging
-0.02
-200
-100
0100
time (ms)200_Fig.2. Time evolution of ECE intensity and n eobtained in a low toroidicity (t) configurationby changing microwave power.
standard config. #41765-41790
6Density Build-up

2.45GHz(klW)

5P

just after the start of the neutral beam injection,
and_plasmas with the electron density of n e 0.2×1019m-3 appeared 10ms after the beam injection.
At the same time, the intensity of OV line emission
increased, which indicates a large number ofelectrons whose energy exceeds the ionization
potential (113eV) were produced in the early phaseof the beam injection.
After that, an additional gas_puff increased ne to over 1×1019m-3.
Figure 2 shows
the time evolution of the ECE_intensity and n e obtained by changing themicrowave power. Just before the timing of the NB_injection (t=210ms), the ECE intensity and n e
increases as increasing the microwave _power. A
clear threshold of the ECE intensity and ne is foundto build up the density.
Figure 3 shows the microwave-power thresholdfor the NB density build-up as a function of themagnetic field strength for the standard
configuration case. At the higher magnetic fieldstrength more than 1.1T, the plasma was built withthe lower (~2kW) microwave power. The lowest
power for the density build-up increases withdecreasing the magnetic field strength. This result
indicates a higher microwave power is required toenlarge the operational space. We are installing andtesting a new 20kW-2.45GHz magnetron system.

1.5(A.U.)

1ECE

CIII
02 (c)

DIA

19-3n (x10 m )IECE, CIII, OVe
W (kJ) (A.U.)

3 (b)ECE(d)I , (A.U.)

the Laboratory for Complex Energy Processes, IAE,
Kyoto University, the NIFS Collaborative Research
Program (NIFS04KUHL001-005, NIFS05KUHL
007, NIFS06KUHL007, NIFS06KUHL009-011,
NIFS06KUHL014-015, NIFS10KUHL030, NIFS10KUHL032) as well as the Grant-in-Aid for Sci.
Research (Kiban (C) 21560857), MEXT.

#41069 |B|=0.83T with 2.45GHz
NBI(a)
Puff
2.45GHz

432
No Build-up

10

0.6

0.8
|B|

AXIS

1(T)

1.2

1.4

Fig. 3. Relation of density build-up by NBI between
microwave power and magnetic field strength.