Dynamic ion shadows behind finite-sized objects in collisionless magnetized plasma flows

Abstract

The potential and density wake behind a finite-sized object in a magnetized collisionless plasma flow is studied with self-consistent numerical simulations. With increasing magnetization of the plasma, the standard picture of ion focusing in the wake for plasmas with large electron to ion temperature ratios becomes invalid. A strong magnetic field parallel to the flow direction leads to a chain of ion depletions in the wake and enhanced ion density at their envelopes. This is due to a novel mechanism of a dynamic ion shadow, which is not the geometrical shadow of the finite-sized object. It corresponds to a change in topology of the wake potential. Complex ion trajectories resulting from electrostatic collisions with the object can lead to significant variations in electrical charging of other objects in the wake.

Ultracold ions wake in dusty plasmas

“…In dusty plasmas under normal conditions, ions streaming past an isolated grain focus behind the grain and give rise to wakefield. It has routinely been a common analytical as well as numerical observation in dusty plasmas [26][27][28][29]. A detailed description of these wakes delineating the grain-plasma dynamics under cryogenic environment is presented here.…”

Molecular dynamics simulations of wake structures behind a microparticle in a magnetized ion flow. I. Collisionless limit with cold ion beam

“…26 and is also studied by us with particle-incell simulations. 25 According to the considerations above, the formation of a dynamic shadow is an intrinsically nonlinear process that is governed by large-angle collisions of the ions with the microparticle. Therefore, dynamic shadows cannot be described by LR theory.…”

“…1(a) and is also observed in PIC simulations. 25 A synopsis of the evolution of the ion density along the z-axis is shown in Fig. 5 for selected values of the magnetic induction.…”

“…22 Since LR theory prescribes the charge on the particle, a self-consistent solution, in which the charge on a second particle is affected by the ion flow, 13,23 requires simulation techniques. Particle-in-cell (PIC) simulations of magnetized wakes 24,25 give the desired self-consistency of charge and forces but are limited to artificial mass ratios, which make comparisons with experiments difficult. In experiments with magnetized plasmas, 26 it was found that the interparticle forces in a field-aligned pair of particles show a strong dependence on the magnetic induction B.…”

Experiments on wake structures behind a microparticle in a magnetized plasma flow

“…25, 073703-1 damping of the wake potential. Self-consistent particle-incell (PIC) simulations 34,35 and molecular dynamics (MD) simulations 36,37 have shown the appearance of ion shadows (regions of ion depletion) and the vanishing of the attractive interaction forces at strong magnetic fields.…”