Linear theory of electron-plasma waves at arbitrary collisionality

Abstract

The dynamics of electron-plasma waves are described at arbitrary collisionality by considering the full Coulomb collision operator. The description is based on a Hermite-Laguerre decomposition of the velocity dependence of the electron distribution function. The damping rate, frequency, and eigenmode spectrum of electron-plasma waves are found as functions of the collision frequency and wavelength. A comparison is made between the collisionless Landau damping limit, the Lenard-Bernstein and Dougherty collision operators, and the electron-ion collision operator, finding large deviations in the damping rates and eigenmode spectra. A purely damped entropy mode, characteristic of a plasma where pitch-angle scattering effects are dominant with respect to collisionless effects, is shown to emerge numerically, and its dispersion relation is analytically derived. It is shown that such a mode is absent when simplified collision operators are used, and that like-particle collisions strongly influence the damping rate of the entropy mode. †

Electron skin depth in low density plasmas

“…There are collisional drift waves with ν ei ∼ ω ci , which still characterize turbulence at the edge of tokamak devices (Jorge, Ricci & Loureiro 2018). Therefore, in order to allow drift waves and their derivatives, such as the electron temperature gradient, the ion temperature gradient and the universal instability, to be described by our analytical formulation, we must prove that it characterizes low frequency, and low wavenumber systems (Jorge et al 2019). In other words, we might show that the time rate γ , and wavenumber k satisfy the conditions γ 2 ω 2 ci , and k 2 δ 2 e 1 (where δ e denotes the electron skin depth), respectively, at the plasma boundary.…”

Improved multispecies Dougherty collisions

“…In figure 1 the difference between collisional (γ) and collisionless (γ collisionless ) damping rates are reported for the numerical (black line) and the analytical calculation (black circles) against the normalized collisionality √ 2ν ee /(k v t,e ). Also in the same figure we show the damping rates obtained with the full FPO 26 , showing that the common practice of using the like-particle Dougherty collision operator yields a unsatisfactory description of wave Landau damping at finite collisionalities.…”

Generalized Collisional Fluid Theory for Multi-Component, Multi-Temperature Plasma Using The Linearized Boltzmann Collision Operator for Scrape-Off Layer/Edge Applications

“…( 15). The limit of the moment averaged collision operator (17) is that it is only valid for quasi thermodynamic equilibrium conditions with the species temperatures being close to the plasma common temperature. However, the one in Eq.…”