26aB04
ヘリオトロンJにおける2.45 GHzマイクロ波補助によるNBIプラズマ着火のモデル解析
Model Analysis of NBI Plasma Start-Up with assistance of 2.45 GHz
Microwaves in Heliotron J羽田 和慶1, 2), 長崎 百伸3), 小林 進二3), 増田 開3), 大島 慎介3), 中村 祐司1), 岡田 浩之3), 南 貴司3),
門 信一郎3), 山本 聡3), 木島 滋3), G.M. Weir3), 釼持 尚輝1, 2), 大谷 芳明1), 呂 湘浔1),
N. Asavathavornvanit1), 村上 弘一郎1), 塚崎 僚1), 白波瀬 一貴1), 神野 洋介1), 小田 大輔1),
中野 裕一郎1), 松田 啓嗣1), 多和田 斉興1), 岸川 英樹1), I. Nutchapol1), 山田 晃生1), 水内 亨3)
K. Hada1, 2), K. Nagasaki3), S. Kobayashi3), K. Masuda3), S. Ohshima3), et al.
1
京都大学エネルギー科学研究科, 2日本学術振興会特別研究員 DC2, 3京都大学エネルギー理工学研究所
1GSES, Kyoto University, 2Research Fellow of Japan Society for the Promotion of Science, 3IAE, Kyoto University

1.00.50.0

 ms ms

 = 3 ms01
2
3
45
6
17
Seed plasma density, ne(@ before NBI) [10 m3]
Figure 1 Dependence of the electron density after amain gas puff on the seed plasma density for the casesof with and without density build-up.

PNBI

QDP

Red line is the experimental data.

1 Black line is the simulation result.

ne, expne, sim

0Te

100

Wsim

Ti01017
1016
1015
190

Wexp

3210

QDP [1020 molecules/s]#56836 4

400
300
200
1000W [kJ]ne(@ after gas puff) [1019 m3]

Exp w/ build-up
Exp w/o build-up

19
3
T [eV] ne [10 m ] P [kW]#5674956755

1.55, and 10 ms are indicated as black closed squares,circles, and triangles, respectively. These reproduce thetendency of the experimental seed plasma density
dependence. The shaded area is supposed to be measured
in the 2015 experiments. Figure 2 shows the time
evolutions of the main variables for the seed plasma
density of 6.0×1017 m3. The simulated electron density
and the stored energy agree with the experimental data
within a factor of 2. Electrons are heated through theCoulomb collisions with fast hydrogen ions produced bymainly the charge exchange collisions of the neutral
beams (NBs) with deuterium ions, and they ionize themain gas puff. The physical processes for the seedplasma density of 0.6×1017 m3 are also discussed, inwhich case the electron temperature is around 10 eV
because of the low fast hydrogen ion density of the orderof 1014 m3. The fast hydrogen ion density has beenfound to be suppressed by the low NB ionizations and by
the charge exchange collisions of fast hydrogen ions with
deuterium and hydrogen molecules.
[1] K. Hada et al., ISHW 2015, P2S3-38

n [m]In a number of stellarator/heliotron devices, plasmas
are initiated by the electron cyclotron resonanceheating. This method limits the operating magnetic
field strength. Plasma start-up using only neutral beam
injection (NBI) has been proposed to mitigate thislimitation of the field strength. This is useful for beta
scaling and high beta experiments. In Heliotron J, NBI
plasma start-up has been done with the aid of the seedplasma generated by 2.45 GHz microwaves under thenon-resonance condition before the NBI.
To clarify the physical processes in the density build-up
phase, a zero-dimensional (0-D) model has beendeveloped, which includes the time-dependent particle
and energy balance equations for fast hydrogen ions fromNBI, molecules (D2 and H2), molecular ions (D2+ andH2+), ions (D+ and H+), and electrons.
Figure 1 shows the dependence of the electron density
after the main gas puff on the seed plasma density, wherered open circles and blue crosses show the cases of withand without density build-up in the experiments,
respectively [1]. The threshold in the seed plasma
density for the density build-up is deem to be in theshaded area, which area was not measured in the lastyear experiments due to the difficulty in the control ofthe pre-filled gas pressure. The simulated dependences
for the particle and energy confinement time of  = 3,

[H+f]
[D2]
200

210
220230t [ms]
Figure 2 Time evolutions of the NBI power (PNBI), themain gas puff (QDP), the electron density (ne), the storedenergy (W), the electron and ion temperature (Te and Ti,respectively), the fast hydrogen ion density ([Hf+]), andthe deuterium molecule density ([D2]).