22P100-P
Measurement of Neutral Beam Attenuation Using
Atomic and Molecular Database on LHD
LHDにおける中性粒子ビーム減衰計測の原子分子データベースの活用
Katsunori Ikeda, Masaki Osakabe, Izumi Murakami, Daiji Kato, Masashi Kisaki, Yasuhiko Takeiri,
Katsuyoshi Tsumori, Haruhisa Nakano, Kenichi Nagaoka and LHD experiment group
池田勝則，長壁正樹，村上 泉，加藤太治，木崎雅志，竹入康彦，津守克嘉，中野治久，永岡賢一，LHD実験グループ
National Institute for Fusion Science322-6, Oroshi, Toki, Gifu 509-5292, Japan
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
Hydrogen Balmer emission (Hα: n = 3 → 2) emitted from neutral beam particles from NBI had been
observed by Doppler spectroscopy on LHD. Large signal drop was appeared on beam-emissions after asmall carbon pellet injection on hydrogen discharge. Beam stopping and emission coefficient on the atomic
database had been applied to the beam attenuation analysis. Calculated beam-emission flux well fitted tothe measured signals, and this result has confirmed strong beam attenuation after the carbon pellet injection
along the beam injection path.

1. Introduction
Neutral beam injection (NBI) is a powerful anduseful heating for fusion experiment devices. Detailof beam heating power is required for effective
beam heating for the Large Helical Device (LHD)[1]. Hydrogen beam particles are ionized into
plasma and trapped with confinement magnetic
field. Other residual beam particles pass throughplasma with optical emissions of hydrogen Balmerlines. This visible beam-emission with informationsof beam attenuation can be measured easily byDoppler spectroscopy [2-4]. However the local
beam attenuation along the beam injection path isdifficult to obtain only using a signal intensity ofbeam-emission. We will report a diagnostic method
and the beam-emission signals on LHD. We
calculated the beam-emission intensity using thebeam-stopping coefficient and beam-emission
coefficient on an atomic database. Finally, we
estimated beam deposition power with assuming
carbon fraction in a hydrogen discharge.
2. Beam-Emission Diagnostic and Signals
Optical lines of sights (LOS) were set along theneutral beam (BL3) injection path [2,3] as shown inFig. 1. The angles between the beam path and LOS
are 62.4° and 134.7°. The wavelength of hydrogen
optical emission (Hα) from neutral beam particle
was shifted by the Doppler effect. The beamemission signals were detected using an intensified
charge-coupled device detector cooled to -20 °C
which was positioned at the focal plane of a 25 cm
Czerny-Turner spectrometer. The spectrometricsystem was calibrated using an Urbricht sphere witha standard lamp.
Figure 2 shows a typical example of hydrogen
discharge with carbon pellet injection using five
NBI heating. Total neutral beam (NB) power was
25 MW including a modulated NB from BL4 usingfor a charge exchange spectroscopy to obtain theion temperature profile. Tangential third beam line(BL3), which is as the probe beam for beam
attenuation measurement, injected 4.9 MW constant
NB power as shown in Fig. 2(a). After a small
carbon pellet (φ= 1 mm) injection at t= 3.85 s, theline averaged electron density, which was measured
by a far-infrared laser interferometer (FIR),increased rapidly as much as two times ofmagnitude as shown in Fig. 2(b). Figure 2(c) shows
the intensity of beam-emission signals. ThoseFig. 1. Schematic drawing of neutral beam injectors andline of sights for beam attenuation measurement in LHD.

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Nb (L) = Nb (P )exp(−� LPFig. 2. (a) Bold line is the injection NB power of BL3
and dotted line is the deposition power estimated bybeam attenuation analysis. (b) Line averaged electrondensity. (c) Beam emission intensities at the upstream
and the downstream positions. Lines are beam emission
flux calculated by beam attenuation analysis using
ADAS database on the assumption of decaying a carbon
fraction.

Fig. 3. Electron density and beam attenuation along thebeam injection path.

signals dropped after the carbon pellet injection
considering as strong beam attenuation due to theincreasing of beam stopping cross-section bycarbon impurity. Then the beam-emission signals
gradually increased as decreasing of electrondensity.
3. Application of Atomic Database to Beam
Attenuation Analysis
At the position of L, a local beam-emission flux
Φ(L) is proportional to the product of local electron
density ne(L), neutral beam density Nb(L) and beamemission coefficient ϵcr [4]. Here, we calculated
neutral beam attenuation along the beam injection
path using the effective beam-stopping coefficient
Scr on the Atomic Data and Analysis Structure(ADAS) database [5-7]. Local neutral beam density
is expressed by an exponential decay function asfollows�mne (l)Scr (l)dl),
2E

here Nb(P) is the initial neutral beam density paththrough the beam injection port, and m and E is themass and the energy of beam particles, respectively.
We estimated Scr and ϵcr along the beam injection
path using a hydrogen and carbon mixture model.
When the carbon fraction is assumed 3% at t= 3.9 s
as shown in Fig. 2(c), a large beam attenuation
appears around L= 15.6 m where is the first peak
position of ne along the beam injection path. The
total beam deposition rate increases from 49% to
88% due to increasing carbon fraction, then it
decreases to 60% at t= 4.1 s with decaying to 0.1%
carbon impurities. Relative beam-emission flux Φestimated by the same analysis using the ϵcr also
dropped by increasing carbon, and the recovering
behavior similar to the electron density appears on
Φ in Fig. 2(c). Then we estimated the beam
deposition power by the product of the beam
deposition rate and the port through power asshown in Fig. 2(a). Effective net heating powerincreases to 4.3 MW from 2.4 MW by carbon
impurities. We confirmed strong beam deposition
after the carbon pellet injection.
4. Summary
Beam stopping and emission coefficient on theatomic database had been applied to the beam
attenuation analysis. Calculated beam-emission flux
well fitted to the beam-emission signals measured
from the Doppler spectroscopy on LHD. Thisanalysis is useful to understand for the detail ofbeam heating and the beam attenuation along thebeam injection path.
References[1] Y. Takeiri, O. Kaneko, K. Tsumori et al., Nucl.
Fusion 46 S199 (2006).
[2] Katsunori IKEDA, Masaki OSAKABE, Allan
WHITEFORD, et al., J. Plasma Fusion Res.
SERIES, Vol. 9 pp88-93 (2010).
[3] Katsunori IKEDA, Masaki OSAKABE, Allan
WHITEFORD, et al., J. Plasma Fusion Res.
SERIES, Vol. 8 pp987-990 (2009).
[4] W. Mandl, R. C. Wolf, M. G. von Hellermann and H.
P. Summers, Plasma Phys. Control. Fusion 35
pp1375-1393 (1993).
[5] H. Anderson, M. G. von Hellermann, et al., PlasmaPhys. Control. Fusion 42 pp781–806 (2000).
[6] H. P. Summers “Atomic Data and Analysis Structure
User manual 2nd edition ver. 2.7” (2004).
[7] H. P. Summers, H. Anderson, T. Kato and S.
Murakami “Hydrogen Beam Stopping and BeamEmission Data for LHD” NIFS-DATA-55 November(1999).

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