Ideal Coulomb Plasma Approximation in Line Shape Models: Problematic Issues

Abstract

In weakly coupled plasmas, it is common to describe the microfield using a Debye model. We examine here an "artificial" ideal one-component plasma with an infinite Debye length, which has been used for the test of line shape codes. We show that the infinite Debye length assumption can lead to a misinterpretation of numerical simulations results, in particular regarding the convergence of calculations. Our discussion is done within an analytical collision operator model developed for hydrogen line shapes in near-impact regimes. When properly employed, this model can serve as a reference for testing the convergence of simulations.

Ion Dynamics Effect on Stark-Broadened Line Shapes: A Cross-Comparison of Various Models

“…The main advance with respect to the unified theory is that the collision operator accounts for the finite lifetime of the atom during each collision; this lifetime yields an effective range for the action of the microfield of the order of v/γ, whereγ is a typical matrix element of the collision operator (see the discussion in [41]). This model (and its adaptation to electrons) does not lead to a divergent collision operator if the Debye length is assumed infinite, which is in contrast to standard hydrogen models (see [42]); this makes it suitable for the presented cases, provided the perturbing species under consideration is strongly dynamic.…”

ZEST: A Fast Code for Simulating Zeeman-Stark Line-Shape Functions

“…Taking into account the interference terms in the electronic collision operator may be also important, as shown in [29] for lithium-like satellites of argon. It may also be interesting to study different approximations for the collision operator [39], especially in the limit of weakly coupled plasmas [40] or when accounting for a magnetic field [41]. Another interesting development is the implementation of penetrating collisions which can be taken into account analytically in the case of hydrogen [42] and hydrogen-like ions [43] through an ad hoc theory.…”

Stark Broadening from Impact Theory to Simulations

“…For the weak coupling conditions assumed, a large number of particles (several thousand commonly) is retained in a cube with a size larger than the Debye length. Such a model provides a good approximation for the time-dependent electric field in a weakly coupled ion plasma at equilibrium, although it suffers from inaccuracies, especially if the size of the box is not large enough [23]. We show in Figure 1 the time dependence of one component of the ionic electric field calculated at the center of the box for an electron density N e = 10 19 m −3 , and a temperature T = 40,000 K. The electric field is expressed in units of E 0 = 1/ 4πε 0 r 2 0 , where r 0 is the average distance between particles defined by r 3 0 = 3/(4πN e ).…”