Abstract
Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.
Highlights
Owing to its physical properties of high melting temperature, excellent thermal conductivity, low sputtering rate and low affinity for tritium [1,2], tungsten has been used as a plasma-facing material in several magnetic confinement fusion facilities [3,4,5,6] and is planned to be used in the divertor region having the highest heat load in the International Thermonuclear Experimental Reactor (ITER)tokamak [7]
X-ray emissions from highly charged tungsten ions can be used as diagnostic probes to reflect the information on the fusion plasmas
A recently-developed computational code, REIE06 [38,59], is utilized to calculate electron-impact excitation cross-sections that is based on the fully-relativistic distorted-wave (RDW)
Summary
Owing to its physical properties of high melting temperature, excellent thermal conductivity, low sputtering rate and low affinity for tritium [1,2], tungsten has been used as a plasma-facing material in several magnetic confinement fusion facilities [3,4,5,6] and is planned to be used in the divertor region having the highest heat load in the International Thermonuclear Experimental Reactor (ITER). 3d) atomic transitions have great significance in that they are suitable for fusion plasma modeling and diagnostics, since the radiations involving the 3d subshell are very intense [13] Because of that, these charge states of tungsten are selected to study X-ray polarization in the present work. Charge state distribution in plasmas, X-ray emission spectra and transition properties following electron-impact excitation (EIE) and ionization, as well as dielectronic recombination (DR).
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