The dispersive Alfvén wave in the time-stationary limit with a focus on collisional and warm-plasma effects

Abstract

A nonlinear, collisional, two-fluid model of uniform plasma convection across a field-aligned current (FAC) sheet, describing the stationary Alfvén (StA) wave, is presented. In a previous work, Knudsen showed that, for cold, collisionless plasma [D. J. Knudsen, J. Geophys. Res. 101, 10761 (1996)], the stationary inertial Alfvén (StIA) wave can accelerate electrons parallel to a background magnetic field and cause large, time-independent plasma-density variations having spatial periodicity in the direction of the convective flow over a broad range of spatial scales and energies. Knudsen suggested that these fundamental properties of the StIA wave may play a role in the formation of discrete auroral arcs. Here, Knudsen’s model has been generalized for warm, collisional plasma. From this generalization, it is shown that nonzero ion-neutral and electron-ion collisional resistivity significantly alters the perpendicular ac and dc structure of magnetic-field-aligned electron drift, and can either dissipate or enhance the field-aligned electron energy depending on the initial value of field-aligned electron drift velocity. It is also shown that nonzero values of plasma pressure increase the dominant Fourier component of perpendicular wavenumber.

A two-fluid model describing the finite-collisionality, stationary Alfvén wave in anisotropic plasma

“…For the anti-parallel electron drift (APED) case shown, the StIA wave accelerates electrons in the direction of their initial drift and depletes the background plasma density. Knudsen (1996) and Finnegan et al (2008) characterize the general properties of the StIA and the stationary kinetic Alfvén (StKA) wave in more detail.…”

“…Previous studies of non-linear Alfvén waves made in the wave-frame (e.g., Hasegawa and Mima, 1976;Kotsarenko et al, 1998;Wu, 2003;Dubinin et al, 2005;Stasiewicz, 2005) have assumed that the background plasma is at rest in the lab-frame V j =0 so that d/dt=−V ph ·∇. Studies of the stationary Alfvén wave (StA) (e.g., Knudsen, 1996;Finnegan et al, 2008) however consider the wave to be stationary in the lab-frame V ph =0 and that the background plasma drift is non-zero V j =0 in the lab frame so that d/dt=V j ·∇. Although both approaches describe solutions in the wave frame, each approach (d/dt=(V j −V ph )·∇ in the wave frame or d/dt=V j ·∇ in the lab frame) is associated with a different phenomenon in that the first case involves a fluctuating, traveling pattern and the second case involves a non-fluctuating, non-traveling pattern.…”

Integrated campaign to study the stationary inertial Alfvén wave in the laboratory and space regimes

“…The StIA wave-field geometry including initial particle drifts is shown in figure 1. Knudsen's model has been generalized to include the effects of electron and ion collisional resistivity, as well as non-zero thermal pressure [6,7]. The generalized model describes the stationary Alfvén (StA) wave in both the inertial (β < m e /m i , k ⊥ λ e ∼ 1) and kinetic (β > m e /m i , k ⊥ ρ i ∼ 1) regimes, and is capable of making predictions of StA wave signatures in laboratory plasma.…”

“…The perturbed magnetic field lies along the y-axis. Knudsen [1], for space conditions, and Finnegan et al [6] for laboratory conditions, portray the spatial, pulse-like nature of the perturbed density pattern and the associated electron acceleration that are predicted for the case in which the wave becomes nonlinear.…”

“…The goal of the space-plasma physics campaign is to evaluate this suggestion through laboratory experiment, analytic theory and computer simulation. The original StIA-wave model of uniform plasma convection across field-aligned current sheets has been generalized for laboratory-relevant plasma parameters [6], resulting in the conclusion [7] that significant StIA-wave signatures should be observable in the large plasma device upgrade (LAPD-U) at UCLAs Basic Plasma Science Facility (BAPSF). Here, laboratory results from the West Virginia University Q-Machine [9], using barium-ion plasma, and from LAPD-U [10], using helium-ion plasma, are presented.…”