27pB01
LHDにおける中性水素ダイナミクスの分光研究における中性水素ダイナミクスの分光研究
Spectroscopic Diagnostics of the Hydrogen Dynamics in LHD
藤井 恵介1，四竈 泰一1，後藤 基志2，森田 繁2，蓮尾 昌裕1Keisuke Fujii1, Taiichi Shikama1, Motoshi Goto2, Shigeru Morita2, Masahiro Hasuo1
1

京都大学工学研究科
2
核融合科学研究所
1
Department of Engineering, Kyoto university
2
National Institute for Fusion Science
1. Introduction
In the fusion devices of magnetic plasma
confinement, neutral hydrogen molecules andatoms are mainly generated from desorption or
recombination on the first walls. Some of themtravel toward the plasma and are ionized by electronimpacts. Since the outflux of charged particles fromthe confined region is blanced with the ionization
flux of the hydrogen atoms and molecules a steadycondition, the dynamics of the neutrals have great
influence on the confinement performance. For
establishing a high-performance plasma, it isimportant to understand and control their dynamics[1,2].
The dynamics have been frequently observed byemission measurements. In simple emission
measurements, the line integrated intensity isobserved and no spatial information along the lineof sight (LOS) is usually obtained. However,
Weaver et al. have proposed a method to determine
the two emission locations of the Balmer-α line
along LOS from comparisons of its Zeeman split
and the spatial distribution of the magnetic field [3].
For the purpose of further improving thistechnique, we recently demonstrated a method toobserve several emission spectra of hydrogen atoms
and molecules simultaneously with developing a
multi-wavelength high-resolution spectrometer[4,5]. During these researches it has been found thatline profiles of the Balmer-series emissions havesubstantial wings, which reflect the existence ofhigh velocity neutral atoms [6].
In this paper, we briefly review our recent
progresses.
2. Experiment and Results
Figure 1(a) shows a poloidal cross section ofLHD. We observe the hydrogen spectra with twoLOSs with the perpendicular linear polarization
components resolved. Details of the measurement
system are explained in detail in ref. [4,5].

Fig.1 (a): A poloidal cross section of LHD andlines of sight (LOS1 and LOS2). Derived
emission locations and intensities are shown bycenters and areas of circles, respectively, by thespectral analysis. (b): Simulated density
distributions of hydrogen molecules (graycurve), cold atoms (black solid curve) and hotatoms (black dotted curve) along LOS2.

Fig.2 An example of the polarization resolved
spectra of (a): the Balmer-α, (b): -β, (c): -γlines of hydrogen atom and (d): the Q1 lines in
the Fulcher-α band with the vibronictransitions of v’ = v” = 0 and 2. The
instrumental widths are shown by intervals of
the two vertical bars. The reconstructed profiles
by the spectral analysis are shown by boldcurves.

In figure 2, we show an example of the observed
spectra of the hydrogen atomic emissions (a-c) andmolecular ones (d). Split structures and theirpolarization dependences are clearly seen, which
are due to the Zeeman effect. From the analysis of
the line profiles, in which two localized emission
locations and sum of three Maxwell distributions as
the atom velocity distributions are assumed, theobserved profiles are well reconstructed and theemission locations and the intensities along LOSs
are derived as shown in figure 1(a). The analyticalmethod is described in ref. [7]. It is found that themolecular emission locations are close to thedivertors than the atomic ones. It suggests hydrogentransport; the desorbed molecules from the divertor
plates are ionized and dissociated near the divertor
legs, and the generated atoms are ionized close to
the last closed flux surface (LCFS).
In figure 3, we show the Balmer-α spectral
profiles observed for LOS1 and LOS2 with alogarithemic vertical axis. It is found that thespectrum observed for LOS2 has larger wings thanthat for LOS1. The wings are attributed to theemissions from the high velocity atoms. However,such wing profiles are not reconstructed with theconventional spectral analysis.
We develop a one-dimensional hydrogentransport model which concerns dissociation andionization of molecules, and ionization and charge
exchange collisions of atoms. The simulated density
distribution of hydrogen atoms and molecules along
LOS2 are shown in figure 1 (b). In the figure, theblack solid curve shows the density of cold atoms
which are generated via dissociation while thedotted one shows that of hot atoms generated via
charge exchange collisions with protons. It can beseen that the hot atoms exist even in the core regionof LHD.
We reconstruct a Balmer-α spectrum from thesimulated spatial and velocity distribution taking
the Doppler and Zeeman effects into account. The
reconstructed spectrum is shown in figure 4 by athick curve. The simulated spectrum also showswings.
In the figure, we also plot the simulated spectral
components which are emitted in the regions of ρ <0.4, 0.4 < ρ < 0.8, 0.8 < ρ < 1, and, 1 < ρ, where ρ
is a normalized radius of LHD, which is a measureof the magnetic flux surfaces (Here, ρ = 0 and 1
indicate the magnetic axis and the LCFS,respectively). It can be seen that the emission fromthe core plasma is dominant in the line wings. It isconsistent to the small wing intensity in theobserved spectrum for LOS1.

Fig.3 The e-ray components of the observed
Balmer-α spectra for (a): LOS1 and (b):LOS2.
The vertical axis is logarithmic. The
reconstructed spectra by the conventional
analysis are shown by bold curves.

Fig.4 The e-ray components of the observed
Balmer-α spectra for LOS2 (open circles) andthereconstructedprofile
bytheone-dimensional transportation model (thickcurve). The emission components emitted in
the core regions and edge region are also
shown by thin curves.
References[1]. F. Wagner, G. Becker, K. Behringer, et al.: Phys. Rev.
Lett. 49 (1982) 1408.
[2]. N. Ohyabu, K. Narihara, H. Funaba, et al.: Phys. Rev.
Lett. 84 (2000) 103[3]. J. L. Weaver, B. L. Welch, H. R. Griem, et al.: Rev.
Sci. Instrum. 71, 1664 (2000)[4]. K. Fujii, K. Mizushiri, T. Nishioka, et al.: Rev. Sci.
Instrum. 81, 033106 (2010)[5]. K. Fujii, T. Shikama, A. Iwamae, et al.: Plasma andFusion Res. 5, S2079 (2010)[6]. K. Fujii, K. Mizushiri, T. Nishioka, et al.: NIMA 623,620 (2010)[7]. A. Iwamae, M. Hayakawa, M. Atake, et al.: Phys.
Plasmas 12, 042501 (2005)