ABSTRACT
IAEA-F4-TM-42581
IAEA Technical Meeting on Atomic, Molecular and Plasma Material Interaction Data for
Fusion Science and Technology
Experimental evaluation of
W recombination and Ionization rates/cross-sections*
T. Nakanoa†
a
Japan Atomic Energy Agency, 801-1, Mukoyama, Naka, Ibaraki, 311-0193, Japan
E-mail address of main author: nakano.tomohide@jaea.go.jp
It has been decided that ITER (International Thermonuclear Experimental Reactor) will
be operated with tungsten (W) divertor from the day one because of low tritium retention
property of W. However, due to high atomic number (=74), W ions tend to accumulate at the
plasma core, and strong line radiation from the W ions reduces the plasma temperature. Thus,
one of the issues in plasma operation with W divertor is to prevent W ions from penetrating
plasmas towards the core, 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 to
calculate fractional abundance of Wq+ ion (q: charge state), and photon emission coefficients,
which are calculated with a collisional-radiative model, are needed to determine Wq+ density
from the measured intensity of a Wq+ spectral line. Hence, uncertainty of the determined W
density heavily depends on uncertainties of the atomic data in addition to uncertainty of the
measurement. However, in most cases, calculated W atomic data without uncertainty
evaluation are used in the analysis. Therefore, it is very difficult to mention the uncertainty of
the determined W density. This motivates experimental evaluation of the calculated W atomic
data.
This talk presents two experimental evaluations of the W atomic data: one is evaluation
of a ratio of W44+ ionization rate over W45+ recombination rate performed in a thermal plasma
of JT-60U tokamak. The other is evaluation of a ratio of W44+ ionization cross-section over
W45+ recombination cross-section in a mono-energy plasma of Tokyo EBIT device. One of
the advantages of this method is cancellation out of electron temperature/energy dependence
of excitation rate/cross-section from 4s to 4p level, enabling direct conversion of an intensity
ratio of W44+ 4s-4p spectral line over W45+ 4s-4p spectral line to a density ratio of W44+ over
W45+ by using a coronal model, which can be compared to calculated W44+/W45+ density ratio.
Comparison in the thermal plasma of JT-60U shows good agreement within 30%,
indicating that the ratio of W44+ ionization over W45+ recombination rates calculated by FAC
are evaluated to be accurate within 30%. In addition, comparison in the mono-energy plasma
of Tokyo EBIT also shows good agreement except for some peaks due to resonant structures
of dielectronic recombination. Reasons for this disagreement are not yet known. Finally, this
talk makes a proposal for potential diagnostic lines in ITER: W62+ 3s-3p spectral line and
*
Acknowledgements: This work is partly supported by JSPS KAKENHI Grant-in-Aid for Young Scientists (B)
24760707, and a collaborative work with University of Electro-Communications.
1
I. M. Author1 and I. M. Author2
W63+ 3s-3p spectral line together with a similar evaluation method to those described above
for W44+ and W45+ 4s-4p spectral line.
2