Electron-impact excitations of highly charged tungsten ions and polarization study of their successive photon decay

Abstract

Fully relativistic distorted wave theory has been utilized to study the electron-impact excitation of highly charged tungsten ions viz. Y-like (W35+), Sr-like (W36+), Rb-like (W37+) and Br-like (W39+). Electric dipole transitions pertaining to n = 4 → n′ = 4 states have been considered in these four ions. The electron excitation cross-sections are calculated for these ions in the wide range of electron-impact energies from excitation threshold to 20 keV. The required relativistic bound states wave functions for the initial and excited states of the ions are obtained using GRASP2k code. The accuracy of the computed wave functions is ascertained by comparing the calculated energies and oscillator strengths for the considered transitions with the available theoretical and experimental results. For the direct application of the cross-sections to the plasma modelling our calculated cross-sections are fitted to suitable analytical expressions. Further, the degree of linear polarization of the emitted photons due to the decay of the electron from the excited tungsten ions to their respective ground states is also calculated using density matrix theory. There are no previous calculations available for the cross-sections and polarizations to compare with our results of these ions.