Flowing plasma rearrangement in the presence of static perturbing fields

TL;DR

This paper investigates how static electromagnetic perturbations influence plasma flow and particle confinement, revealing the existence of O and X wave perturbations and their potential to form barriers or wells depending on flow direction.

Contribution

It introduces a simplified slab model to self-consistently analyze electromagnetic fields in flowing plasma with static perturbations, identifying conditions for O and X wave perturbations and their effects.

Findings

Identification of O and X wave perturbations in flowing plasma.

Screening of perturbations at electron skin depth in dense plasmas.

Ponderomotive potential depends on flow velocity and can act as barriers or wells.

Abstract

Charged particles interacting with electromagnetic waves have a portion of their energy tied up in wave-driven oscillations. When these waves are localized to the exhaust of linear magnetic confinement systems this ponderomotive effect can be utilized to enhance particle confinement. The same effect can be derived for particles moving via an $\mathbf{E} \times \mathbf{B}$ drift into a region of a static perturbation to the electromagnetic fields which has a large wave vector component in the direction of the motion. In this work we use a simplified slab model to self-consistently solve for the electromagnetic fields within the fluid flowing plasma of a static flute-like ($k_\parallel = 0)$ perturbation, and evaluate the resulting ponderomotive potential. We find that two types of perturbations can exist within the flowing plasma, which are an O wave and an X wave in the frame moving with the fluid. In the case of tenuous plasma, these perturbations are magnetostatic or electrostatic multipole-analog perpendicular to the guiding magnetic field in the lab frame, respectfully. For denser plasmas, the O wave-like perturbation is screened at the electron skin depth scale, and the X wave-like perturbation is a combination of a similar perpendicular electric perturbation and parallel magnetic perturbation. The ponderomotive potential generated in the X wave-like case is gyrofrequency-dependent, and can be used as either potential barriers or potential wells, depending on the direction of the flow velocity.