Effect of directional energetic electrons on the plasma density diagnostic

We have theoretically investigated how a small fraction of energetic beamed electrons influences the diagnostics of the electron density in hot plasmas, based on the intensity ratio R of the helium-like forbidden line to the intercombination lines. Elaborate calculations of the intensity ratio R have been performed for Ne8+ ions over the range of electron densities 109–1013 cm−3 using an electron distribution (model) that includes both Maxwellian isotropic and monoenergetic beam components. By taking into account all important transitions among the 117 magnetic sublevels of the 1s2 and 1snl (n = 2–4) configurations, a collisional-radiative model has been applied for determining the populations of the upper-magnetic sublevels of lines. The required collision strengths due to both electron components were computed semi-relativistically in the complementary distorted-wave and Coulomb–Bethe methods. The results are given for temperatures Te of the Maxwellian electron component in the range 2–5 × 106 K and for kinetic energies e0 of the monoenergetic electron component between 0.95 and 4 keV. At low Te and e0 not too high, the anisotropy of the intensity angular distribution of lines is found to have an appreciable effect on the R ratio. The electron density inferred from the intensity ratio R without including the beam effect can be significantly overestimated or underestimated depending upon the emission angle relative to the electron beam direction.