Polarization of the nf → 3d (n=4, 5, 6) x-rays from tungsten ions following electron-impact excitation and dielectronic recombination processes

•EIE and REC cross sections of W42+-W46+ ions are calculated for the first time.•Polarizations of strong nf→3d x-ray lines from EIE and DR are calculated.•The polarizations for the same line but from EIE and DR are found to be different.•The present results are expected be used for plasma diagnosis in ITER.

Electron-impact excitation and resonant electron capture cross sections to the specific magnetic sublevels as well as the polarization of the strong nf→3d (n=4, 5, 6) x-ray emitted from Ni-like through Ge-like tungsten ions have been studied systematically by using a fully relativistic distorted-wave method. We compare the polarizations for the same x-ray but from the above two different processes for the first time. It is found that the polarization degrees of x-ray following both the electron-impact excitation and the dielectronic recombination are totally different. Because the electron-impact excitation dominates in hot and dense plasmas and the dielectronic recombination plays a key role in low-density plasmas which are cooled and recombining by capturing continuum electrons, we hope that the specific plasmas conditions could be assessed by using these x-ray polarizations.