05aE12P
高ダイナミックレンジBalmer-線分光法によるLHDコアプラズマ中水素原子密度のポロイダル分布の評価
Evaluation of the poloidal density distribution of neutral hydrogen atoms in
LHD core plasmas by high dynamic-range Balmer-α spectroscopy
藤井恵介1，後藤基志2，森田繁2，蓮尾昌裕1
FUJII Keisuke1, GOTO Motoshi2, MORITA Shigeru2, HASUO Masahiro1
1京大工， 2核融合研

1Kyoto Univ, 2NIFS

For a magnetically confined fusion plasma, studyof neutral hydrogen transport in the core region isimportant to understand the source distribution ofelectrons and protons. Since hydrogen atoms arefree from magnetic field, their density distribution
may depend not only on the normalized radius, ,
but also on the poloidal angle, .
Recently, we found that Doppler shifted
Balmer- emission of hydrogen atoms in the coreregion can be detected in far wings of the line
profile [1]. In this work, we evaluated nH(, ) fromthe Balmer-line profiles observed for an LHD
plasma by multiple lines of sight and a Monte-Carlosimulation for hydrogen transport.
In the simulation, we assume that the poloidal
distribution of atom flux flowing into the coreregion from the outmost surface of the plasma, [m-2/s], has asymmetricity caused by large
atom flux from the helical divertor; its 
dependence is given as()1cos()2cos(2)(1)
where is the average atom flux.  and 
represent the asymmetricity. We trace trajectories
of hydrogen atoms from the outmost surface withtaking the electron impact ionization and proton
impact velocity change into account. Here, we use
spatial distributions of ne and Te measured by theThomson scattering method and assume ne = np andTe = Tp, where ne and Te are the density andtemperature of electrons, respectively, and np and Tp
are those of protons. After 107 traces, nH(, ) andatomic velocity distribution are statisticallysimulated.
From nH(, ) and the velocity distribution, we
reconstruct the Balmer-line profiles considering
the emission rate of atoms, Doppler shift of theemission, and the emission integration along theline of sight. And then, we determine and
by fitting the reconstructed spectra to the observed
ones. The result of the fit is shown by the gray solid
curves in figure 1. The result shows a goodagreement. It is noted that the result without theasymmetricity of the flux, i.e. = = 0, does not
fully represent the observed spectra as shown by thedashed curves in figure 1.
The evaluated nH(, 0) and nH(, /2) are shownin figure 2. Poloidal asymmetricity is clearly seen.
In the outside region ( > 1.1), nH(, 0) is evaluatedto be larger than nH(, /2) reflecting the higher
atom flux from the helical divertor. On the other
hand, in the core region, the tendency reverses
reflecting the horizontally elongated shape of theLHD plasma.

Fig.1 Dots: The Balmer- spectra observed with (a)edge and (b) central view ports of the LHD. Insets
show the poloidal cross section and the lines ofsight. The gray solid curves show the reconstructedresult with asymmetric atom flux. The gray dashedcurves show the result with symmetric atom flux.

Fig.2 Evaluated atom density distribution at  = 0and /2. The inset shows the poloidal cross sectionof LHD.
[1] K. Fujii et al, Phys. Plasmas 20, 012514 (2013).