Contribution of Liénard–Wiechert potential to the broadening of spectral lines by electron collisions in plasmas

• Published in: Physics of plasmas 2022-09, Vol.29 (9)
• Main Authors: Arif, K., Meftah, M. T., Chenini, K., Douis, S., Ben Nana, Y., Gossa, H.
• Format: Article
• Language: English
• Subjects: Collision dynamics; Electric fields; Emitters (electron); Fine structure; Free electrons; High temperature; Hyperbolic trajectories; Line broadening; Line spectra; Plasma physics; Relativistic effects
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/5.0085698

In this work, we have calculated the relativistic collision operator representing the line broadening, by collision with free electrons, of isolated lines emitted by hydrogen-like ions (Ly-α line 2 p   2 P 3 / 2 o → 1 s   2 S 1 / 2) of hydrogenic ions FeXXVI, CrXXIV, and CoXXVII in the temperature range of 10 8 to 5 × 10 9   K and electron densities of 1021 to 10 26 cm − 3. To accomplish this task, we have considered the fine structure of these ions and taking into account the relativistic effects related to the free electrons. Specifically, two relativistic effects are considered: the electric field of Liénard–Wiechert, created by the free electron at the emitter ion, and the modification of the hyperbolic trajectory due to the dependent mass on the free electron velocity. The average over the velocities of the free electrons is accomplished by using the Maxwell–Juttner distribution, which is more adequate for the fast (relativistic) electrons. The results are compared to the classical case (when the electric field is the Coulomb's field) to Doppler broadening and to some experimental results (K. Koyama and M. G. Haines) available in the literature. It turns out that, at high temperatures and high densities, the Stark broadening by the relativistic electrons overcomes the Doppler broadening.