22P099-P
Spectroscopy of Highly Charged Tungsten Ions
with the Electron Beam Ion Traps
タングステン多価イオンのEUV分光測定	 
H. A. Sakaue1, D. Kato1, I. Murakami1, N. Yamamoto2 and N. Nakamura3
坂上裕之 1，加藤太治 1，村上泉 1，山本則正 2，中村信行 3
1

National Institute for Fusion Science, Toki, Gifu 509-5292, JAPAN
2
Chubu University, Kasugai, Aichi 487-8501, JAPAN3
Institute for Laser Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, JAPAN

核融合科学研究所	  〒509-5292	  土岐市下石町322-6	 
中部大学 〒487-8501	  春日井市松本町1200
電気通信大学レーザー研	  〒182-8585	  調布市調布ヶ丘1-5-1
We present spectra of highly charged tungsten ions in the extreme ultra-violet (EUV) range observed by using
the electron beam ion traps. The electron energy dependence of spectra is investigated for several electronenergies from 490 to 1440 eV. The previously unreported lines are presented in the EUV range, and the electronenergy dependence of them are measured.

Tungsten is a strong candidate for the materialof the plasma-facing components, such as the firstwall and divertor plates, in ITER because it has
excellent physical properties, such as a low
sputtering yield, a high melting point, a low tritium
inventory, and so on. However, since high particle
and heat fluxes would cause serious damages tosuch components, tungsten is considered to be oneof the most abundant impurities in the ITER plasma.
Emission lines of highly charged tungsten ions thus
play an important role in the spectroscopic
diagnostics of the ITER plasma, and consequently
the spectroscopic data of tungsten ions are strongly
needed. To date, the spectroscopic studies of highly
charged tungsten ions have been carried out by
using high temperature (several keV) plasmas [1-2]and electron beam ion traps (EBITs) [1, 3-4] withrelatively high electron energies (several to several
tens keV). However, there is not yet enough data. In
particular, the spectral data of moderate charge state
tungsten ions (W10-30+) are quite limited.
For the systematic spectroscopic studies oftungsten ions, we have been using two kinds ofEBITs. One of them is the high-energy EBIT
(Tokyo-EBIT) [5] constructed at the University ofElectro-Communications (UEC), and another is thelow-energy compact EBIT (CoBIT) [6,7] developed
for spectroscopic studies of moderate charge stateions. Figure 1 (a) and (b) shown the present
experimental setup for CoBIT and the Tokyo-EBIT.

Fig.1 The experimental apparatuses of CoBIT andTokyo-EBIT

We have constructed two CoBIT, and installed
them at the UEC and National Institute for Fusion
Science. The electron energy range of CoBIT andthe Tokyo-EBIT is 0.1 - 2.5 keV and 2 - 200 keV,
respectively, and the accessible charge states areabout 10 – 40 and 40 – 74, respectively. The
complementary use of them thus enables us toaccumulate the atomic data of tungsten ions with avariety of charge states.
In this paper, we present extreme ultraviolet

(EUV) spectra obtained with the electron energy
range 410 - 1440 eV. Grazing-incidence flat-fieldgrating spectrometers especially designed for
CoBIT was used for EUV emission in the 1 - 20 nm
range. The previously unreported lines arepresented, and some of them are identified bycomparing the wavelengths with theoretical
calculations.
Figure 2 shows EUV spectra obtained by using
CoBIT with electron energies between 670 and
1210 eV. The corrections for the spectrometer
response and the detector efficiencies were applied
to the spectra shown in this figure. It is clear fromthe figure that the overall EUV spectra show
significant dependence on the electron energy. Thetwo peaks denoted by A and B are considered to be
the emissions from the maximum charge state ion ateach electron energy because they were not seen in
the spectra with lower electron energies. For
example, when the electron energy Ee increases
from 800 to 870 eV, the maximum tungsten ion
charge q produced in CoBIT is increased from 26+
to 27+. The emission lines of W XXVIII, which
could not been seen at Ee= 800 eV, were observed
at 21.5 Å (Peak A) and 28.3 Å (Peak B) at Ee =870
eV. As electron energy increases from 670 to 1210
eV, the charge states of the ions emitting these lines
vary from W XXIV to W XXXI (W23+ ~ W30+).
In each spectrum, the emission lines from three orfour charge states of highly charged tungsten ionsare observed simultaneously. As the charge stateincreases, wavelengths of these emission lines(Peaks A and B) shift to the shorter
wavelength-region.
The electron energy dependence of line
intensity and its application to the plasma
diagnostics are also discussed.
Acknowledgments
This work is performed with the support and under
the auspices of the NIFS Collaboration Research
program (NIFS09KOAJ003).

Fig.1 Typical EUV spectra of highly charged tungsten
ions obtained at electron energy Ee from 670eV
to 1210eV in CoBIT. IP(q+) is the qth ionizationenergy of tungsten ion.
References[1] T. Putterich et al., J. Phys. B 38, 3071 (2005).
[2] M. B. Chowdhuri et al., Plasma and Fusion Research
2, S1060 (2007).
[3] J. Clementson and P. Beiersdorfer, Phys. Rev. A 81,052509 (2010).
[4] Y. Ralchenko et al. J. Phys. B 40, 3861 (2007).
[5] N. Nakamura et al., Phys. Scr. T73, 362 (1997).
[6] N. Nakamura et al., Rev. Sci. Instrum. 79, 063104(2008).
[7] H. A. Sakaue et al. J. Phys.:Conf. Ser. 163, 012020(2009).