Density dependence of intensity ratios of the 3d → 2p x-ray anisotropic emission from electron-beam excited Ar 13+ ions

Abstract We investigate the ratio R of the intensity of the blended lines 3d 3/2,5/2 → 2p 3/2 over that of the resonance line 3d 3/2 → 2p 1/2 emitted by boron-like Ar 13+ ions after impact excitation by an electron beam. We calculate R as a function of the electron density n e in the range 10 9 –10 13 cm −3 , for incident-electron energies from 0.46 to 5.5 keV. The calculations take into account the anisotropy in the angular distribution of photon emission by considering several angles of observation θ relative to the electron beam direction. A detailed collisional-radiative model that involves 560 magnetic sublevels arising from the 12 configurations 2s 2 2p, 2s2p 2 , 2p 3 , 2s 2 3 l , 2s2p3 l and 2p 2 3 l ( l = s, p, d) is used to determine the populations of upper sublevels of the lines. All basic atomic parameters needed in the calculations, including radiative transition probabilities and collision strengths for transitions between magnetic sublevels, are obtained from the flexible atomic code. The ratio R at the angle θ = 0° is found to be higher than that at θ = 90° by up to 43% for n e = 10 9 cm −3 , but this difference drops with increasing density to become less than 10% above ∼8 × 10 11 cm −3 . The line 3d 3/2 → 2p 3/2 blended with 3d 5/2 → 2p 3/2 is found to enhance the anisotropy of R . The present calculations may be extended to non-Maxwellian hot plasmas having cylindrically symmetric electron velocity distributions, which would be useful for electron density diagnostics of such plasmas.