22P093-P
Spectroscopic study of hydrogen and helium plasmas
水素・ヘリウム衝突輻射モデルによる発光線解析
Toshimitsu Oda1, Keiji Sawada1, Souta Kojima1, Hirotaka Yashiro1, Takanori Yashiro1,Kazunari Taniguchi1, Hiroto Tsuruta1, Naomichi Ezumi2, Motoshi Goto3
小田敏充1, 澤田圭司1, 小島宗太1, 八代博嵩1, 八代嵩憲1,谷口和成1, 鶴田裕人1, 江角直道2, 後藤基志3
1

Graduate school of Sci . and Tec., Shinshu University 4-17-1 Wakasato,Nagano,380-8553, Japan
信州大学大学院工学系研究科 〒380-8553 長野市若里4-17-1
2
Nagano National College of Technology,716 Tokuma, Nagano 381-8550, Japan
長野工専 〒381-8551 長野市徳間716
3National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
核融合科学研究所 〒509-5292 土岐市下石町322-6

For LHD plasmas, using atomic helium collisional-radiative model which includes radiation trapping
effect, the electron temperature and density have been determined from emission intensity of helium atoms.
The population of 31P is dominantly produced by the photo-excitation from the ground state. The
contribution of the electron impact transition from the photo-excited 31P to 31D is nearly the same as thedirect electron impact excitation from the ground state to 31D. The influence of the photo-excitation on theother excited states is small. For RF hydrogen plasmas at Shinshu University, using molecular hydrogencollisional-radiative model, molecular emission lines have been analyzed.

1. Introduction
Understanding of the reactions of atomic andmolecular hydrogen in fusion edge plasmas isessential to improve the performance of the main
plasmas and to reduce the heat flux to the divtertor
wall. In order to investigate the reactions, we havebeen developing collisional-radiative (CR) models
and neutral transport code for hydrogen and heliumspecies. In the models, the electron temperature Te
and density ne are input parameters. In this study,
we are developing spectroscopic methods todetermine them. First, we will discuss an analysisof helium atom emission intensity of LHD plasmas
with a helium CR model, in which radiation
trapping is considered. Second, we are constructing
a CR model of molecular hydrogen, which will be
used to determine Te and ne as well as helium model.
We will discuss an application of the model to RF
plasmas at shinshu University.
2. Helium atom spectroscopy for LHD plasmas
Determining Te and ne from visible emission line
intensities of helium atoms with a CR model is oneof widely used methods [1]. However, the radiation
trapping effect is neglected in many cases. We haverecently proposed a simple and precise method toinclude the radiation trapping effect in the CR
model [2], where the photo-excitation rate from theground state is included as fitting parameter in
addition to Te and ne to reproduce measured line

intensities. The method was applied to RF plasmas(ne ~1016 m-3) at Shinshu University. Measured
intensities of the helium emission lines were well
reproduced by the model, and Te, ne and thephoto-excitation rate were successfully determined.
However, because of the low ne, the contribution of
the photo-excitation to the population density
except for the singlet p states was small.
In order to test the method for high ne, we haveapplied the method to LHD plasmas where thecontribution of the radiation trapping to thepopulation density distribution is expected to be notnegligible. We have analyzed visible helium line
intensities emitted from gas puffed helium atoms inhydrogen plasmas. Figure 1(a) shows measured
spectra (Shot No. 98898). Figure 1(b) shows thepopulation densities of the excited states derived
from the intensities.
We have estimated the relaxation times of themetastable states 21S and 23S, and have adopted thequasi-steady-state approximation to 21S and 23S.
Then the population density of the excited state p,n(p) is given by,n(p)=r1(p)nHene+r2p(p)nHeI2p+r3p(p)nHeI3p+ ･･･ (1)where nHe is the ground state atom density. The firstterm on the right side of eq.(1) is the conventional
ionizing plasma component. The second and thirdterms denote the photo-excitation from the groundstate to 21P and 31P, respectively. I2p and I3p denotethe excitation rates to 21P and 31P from the groundstate by the photo-excitation per atom.
Figure 1(b) shows the result of the fitting by eq.(1).
The experimental population densities are well
reproduced. Obtained Te and ne are 12.7 eV and5x1018m-3, respectively. We can understand thatthese values reflect Te and ne at a position whereemission intensity is maximum along the line ofsight. The population of 31P is dominantly producedby the photo-excitation from the ground state. For
the population of 31D, the contribution of theelectron impact transition from the photo-excited
31P to 31D is nearly the same as the direct electron
impact excitation from the ground state. For theother excited states, the contribution of thephoto-excitation is small. We could not determine
I4p in eq.(1) due to the low intensity of 41P-21S
emission line. However, transitions from 41P toother states by electron impact are expected to besmall because the population densities of 41S and
41D are well reproduced by the model. The
excitation from the photo-excited 21P to other statesis negligible for ne in this plasma.

plasmas at Shinshu University
Hydrogen RF plasmas were produced by a device
at Shinshu University as shown in Figure 2. Figure3(a) shows emission lines measured by echelle
spectrometer. We have identified the wavelength ofmolecular hydrogen emission lines using data inRef. [3]. Figure 3(b) shows emission lines
calculated by the CR model of molecular hydrogen.
The model reproduced the Fulcher band intensity inthe experiment well. We are investigating othermolecular line intensities using the model.

Fig.2 RF Device at Shinshu University

Fig.3 (a) Emission lines of an RF hydrogen plasma atShinshu University. (b) Calculated emission lines.
Fig.1 (a) Spectra observed in LHD plasma (Shot No.
98898). (b) Population distribution. Open circles:
spectroscopic measurement; plus signs: result of theleast-squares fit calculated using eq. (1) with optimized
values ne, Te, I3P, and nHe.

3. Molecular hydrogen spectroscopy for RFReferences[1] M. Goto, JQSRT 76, (2003) 331.
[2] K. Sawada et al., Plasma and Fusion Res. 5 (2010)001.
[3] H. M. Crosswhite, The Hydrogen Molecule
Wavelength Tables of Gerhard Heinrich Dieke,
Wiley-Interscience, New York (1972).