24aD15P
44	 価および	 45	 価タングステンイオンの電離・再結合断面積の実験的な評価	 
Experimental evaluation of W44+ ionization and W45+ recombination
cross-sections	 
仲野友英1，大橋隼人2，中村信行3
NAKANO Tomohide1, OHASHI Hayato2, NAKAMURA Nobuyuki3
原子力機構，2富山大理工，3電通大レーザー
1
JAEA, 2Univ. Toyama, 3Univ. Electro-Communications

-24

10-25

RR

10-26

Tokyo EBIT exp.

10-2720EA

16DI

10844+

445+12NIST EBIT exp.
45+W

-28

2400

2800/W

3200

44+(Cal.)density ratio

10DR/W-23W

102It has been decided that ITER (InternationalThermonuclear Experimental Reactor) will use
tungsten (W) divertor from the day one because of thelow tritium retention property. However, due to highatomic number (=74), W ions tend to accumulate at
the plasma core, and strong line radiation from the Wions reduces the plasma temperature. Thus, one of theissues in plasma operation with W divertor is toprevent W ions from penetrating plasmas towards thecore, and therefore, it is important to measure the W
density at the core quantitatively. To determine the W
density from measured W spectral line intensity,
various atomic data for W ions are needed; ionization
and recombination rates are needed in order tocalculate fractional abundance of Wq+ ion (q: chargenumber), and photon emission coefficients, which arecalculated with a collisional-radiative model, areneeded to determine Wq+ density from the measured
intensity of a Wq+ spectral line. Hence, uncertainty ofthe determined W density heavily depends on
uncertainties of the atomic data in addition touncertainty of the measurement. However, in mostcases, calculated W atomic data without uncertainty
evaluation are used in the analysis. Therefore, it isvery difficult to mention the uncertainty of themeasured W density. This motivates experimental
evaluation of the calculated W atomic data.
This talk presents comparison of a density ratio ofW45+ to W44+ between measurement and calculation.
The measurement was performed in mono-energy
plasmas of Tokyo EBIT device, in order to determine
the W45+ / W44+ density ratio from the intensity ratioof W45+ 4s-4p spectral line (6.2 nm) and W44+ 4s-4p
spectral line (6.1 nm). One of the advantages of thismethod is cancellation of electron energy dependenceof excitation cross-section from 4s (ground level) to
4p (first excited level), enabling direct conversion of
the intensity ratio to a density ratio of W45+ over W44+
by using a coronal model.
On the other hand, the W45+/W44+ density ratio canbe calculated with W44+ ionization cross-section andW45+ recombination cross-section with the assumptionof ionization equilibrium. For the W44+ ionization
cross-section calculation, considered are direct

Cross section ( m )103600Ee ( eV )Fig. Calculated dielectronic recombination (DR),radiative recombination (RR), direct ionization(EI)
andexcitation-autoionization(EA)
cross-sections (left axis), and comparison of
calculated W45+ / W44+ ratio and measured ones
(right axis).
ionization (DI) of 4s electron, and excitation toautoionization levels ( 3d9 4s2 nl , etc ) followed byautoionization to W45+ (excitation-autoionization, EA).
As shown in the figure, the EA cross-section is higher
by one order of the magnitude than the DI
cross-section.
FortheW45+
recombination
cross-section calculation, considered are radiative
recombination (RR) to W44+ and dielectronic
recombination (DR), which starts with electron
capture by W45+ to doubly excited levels of W44+. For
the DR cross-section calculation, this work considers
3d9 4s nl n’l” (n up to 16, n’ up to 100, l and l’ up to12), 3p5 4s nl n’l” (n up to 5), and 3s 4s nl n’l” (n upto 5) as the double excited levels. As shown in thefigure, the DR cross-section is higher in theconsidered energy range than the RR cross-section.
From these four cross-sections, the W45+/W44+ density
ratio is calculated. As shown in the figure, thecalculated W45+/W44+ density ratio is in good
agreement with the measured one in the energy range
over 3000 eV and in fair agreement below 3000 eV.
Including further autoionization (AI) channels after
the electron capture, for instance, AI to inner shell
excited levels of W45+, we could expect reduction of
the DR cross-section, resulting in better agreement
below 3000 eV. This is a future work.