Dielectronic recombination of Cu-like W45+
Introduction
Atomic data need on tungsten (W) for spectroscopic and transport modeling is inevitable for fusion plasma diagnostics nowadays since W is an important component of plasma facing material in various fusion tokamaks as well as in ITER project [1]. Spectral line emission depends on charge state distribution (CSD) in the plasma and the CSD is determined by the balance between ionization and recombination. Dielectronic recombination (DR) is the dominant recombination process for most W ions with the exception of very highly charged ion in fusion plasmas. DR data by a sophisticated theoretical calculation for W is rare and is not available for all W ion stages yet. The experimental DR data exists only for W18+ [2] and W20+ [3].
Cu-like W45+ has been reported to be abundant in a few keV temperature plasma and to emit EUV lines around 12 nm and soft X-ray lines around 6 nm which are applicable for fusion plasma diagnostics [1]. An insightful theoretical prediction and analysis on the DR process for W45+ was previously given by Behar et al. [4]. However, their prediction is only for the DR via the inner-shell and core electron excitations from the ground state ([Ar]) into shell accompanying electron capture, i.e. and .
For plasma modeling DR rate coefficient counted for all possible resonance channels is needed. Hence we have carried out new calculations for DR of W45+ forming W44+ including resonance channels more than and , which were not dealt with in the previous work [4] using FAC (flexible atomic code) [5]. In addition effect of configuration mixing including double core electron transition for complex on the DR cross section and rate coefficient has been investigated which was not considered in the previous work [4].
In Section 2 of this paper the theoretical approach used is described briefly. Calculated DR cross sections and rate coefficients are presented and the resonance structures are analyzed for various core electron excitation types in Section 3. The total rate coefficient obtained by our state-of-the-art calculation is shown and compared with the data given by a simple semiempirical formula [1], [6] which is available on the ADAS database [7] and adopted usually in plasma modeling, and with the very recent data by ab initio calculation [8] from low and intermediate temperatures below the ionization threshold for a photoionized plasma under radiation source [9] to higher temperatures for a collisionally ionized plasma [10]. A summary for our findings is given in Section 4.
Section snippets
Theoretical method
The energy averaged DR cross section in an independent process, isolated resonance (IPIR) and distorted wave (DW) approximation where the interferences between radiative recombination and DR as well as between DR resonances are neglected, can be expressed in atomic units as [11]which is the product of the dielectronic capture (DC) cross section for the recombining state i to the intermediate resonance state j and the radiative stabilizing
Results and discussion
Our calculated DR cross sections and rate coefficients depending on configuration mixing and considered autoionization and radiative decay channels are presented by core electron excitation types of the recombining W45+ ground state [Ar].
Summary
We have calculated DR of Cu-like W45+ forming Zn-like W44+ using FAC and a IPIR-DW approximation. Configuration mixing, AI and RD channels, and energy structures for DR resonances are investigated in detail. Configuration mixing including double electron transition as well as single electron transition significantly alter DR cross sections and Maxwellian rate coefficients due to shift of resonance energy or appearance of additional resonances. The configuration mixing leads to the change in
Acknowledgements
This work was supported by the National R&D Program funded by the Korean Ministry of Science, ICT & Future Planning.
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