Ne IX line G-ratio in a non-Maxwellian and anisotropic plasma

We have theoretically studied how the presence of a small proportion of energetic beam electrons mixed to a bulk of Maxwellian electrons in a hot plasma affects the temperature-dependent intensity ratio G = (x + y + z)/w of the helium-like triplet intercombination (x, y) and forbidden (z) lines to the singlet resonance line (w). By modelling the electron distribution function as a combination of a Maxwellian isotropic component and a monoenergetic beam component, detailed calculations of the G ratio of the Ne8+ lines have been performed for temperatures Te of the Maxwellian component and kinetic energies e0 of the beam component in the ranges 106–107 K and 1.5–25 keV, respectively. A magnetic sublevel-to-magnetic sublevel collisional-radiative model has been used for determining the populations of the upper magnetic sublevels of the four lines at an electron density below 1013 cm−3. Excitations from the ground 1s2 1S0 and metastable 1s2s 3S1 magnetic sublevels to the 1snl (n = 2–4) magnetic sublevels as well as the inner-shell ionization of the lithium-like ion in its ground level were taken into account. All basic atomic data, including the radiative transition probabilities and the collisional excitation and ionization cross sections, were computed using the flexible atomic code. It is found that the contribution of a 5% fraction of the beam component can reduce the G ratio by a factor of 30 at Te = 106 K and of 2.4 at Te = 3 × 106 K. Our calculations also indicate that the effect of directionality of the beam component on G is negligible for e0 above ∼10 keV and that for a given Te, G is practically insensitive to variations in e0 above ∼7 keV. (paper)