Ambipolar diffusion and drift in computational weakly-ionized plasmadynamics

Sheath governing equations in computational weakly-ionized plasmadynamics

“…(24) will collapse to the well-known ambipolar diffusion term for a three-component quasi-neutral plasma (see for instance Ref. [20]):…”

“…As was shown in Ref. [20], there is a computational advantage in doing so: when written in ambipolar form, the charged species transport equations depend less strongly on the potential equation, and this leads to a beneficial reduction of the coupling between the potential and the electron and ion densities. To yield a computational advantage, however, the ambipolar diffusion terms must be written such that they do not depend on the electric field.…”

“…For these reasons, we follow Ref. [20] in which an approach is presented to obtain an exact solution to the ambipolar diffusion coefficient which is free of the electric field. This is in contrast to the ambipolar diffusion method proposed in Refs.…”

“…[20], we can derive the ''ambipolar form'' of the electron conservation equation from the physical model as follows. Let us first define E 0 as the component of the electric field that cancels out the component of the current originating from mass diffusion of the charged species (see the current components in Eq.…”

“…Rewriting the governing equations differently while keeping the physical model the same was the strategy used to reduce the stiffness of the system associated with a quasi-neutral multicomponent plasma model in Ref. [20], with a currentless plasma model in Ref. [21], and with a two-fluid Euler-Poisson plasma model in Ref.…”