Streaming Complex Plasmas: Ion Susceptibility for a Partially Ionized Plasma in Parallel Electric and Magnetic Fields

Abstract

The density response function for streaming ions in homogeneous, parallel electric and magnetic fields is derived self-consistently from kinetic theory. Ion-neutral collisions are treated with the Bhatnagar-GrossKrook collision operator assuming a constant ion-neutral collision frequency. The result accounts for the nonMaxwellian distribution function of the ions and is valid in the full range from weak to strong magnetization. It provides the basis for various linear response calculations in the context of magnetized complex plasmas, where streaming ions interact with highly charged dust particles under the influence of a strong external magnetic field. Magnetic fields play an important role in plasma physics because they allow one to confine and manipulate charged particles externally. Plasma properties such as wave spectra, particle diffusion, heat conduction, or plasma instabilities can be strongly modified when the plasma is magnetized. Strong magnetic fields of several Tesla are not only encountered in magnetic confinement or magnetic liner inertial fusion experiments [1] but have also become of interest for complex plasmas research [2,3]. By adjusting the magnetic field strength it is possible to create plasma states where only the electrons, electrons and ions, or possibly all three charged particle species including the dust particles are magnetized [4]. Several new phenomena have been observed in experiments with magnetic fields, including a slow rotation of the entire dust cloud [5][6][7][8][9], the spinning of dust particles [10], and complicated flow patterns [11]. In recent experiments with strong magnetic fields on the order of a few Tesla, sufficient to magnetize not only the electrons but the ions as well, filaments appeared in the discharge [12]. The dynamics of a dust particle pair also showed a pronounced response to magnetic fields of this magnitude [13]. Experiments performed at the Magnetized Dusty Plasma Experiment (MDPX) at Auburn University [14] further demonstrate that ordered structures of a titanium mesh can be imposed on the dust particles under these conditions. Crystalline and strongly coupled fluid states [15,16] also occur naturally in dusty plasmas due to the strong Coulomb interaction between the grains. Even though the dust particles themselves are difficult to magnetize [17], their screened interaction, and thus, their collective behavior, can be affected significantly by an external magnetic field [18].Dusty plasma experiments are often confronted with ion flows due to electric fields, especially in the sheath region. They affect the charging of the dust grains [19], their mutual interaction due to the formation of wake potentials [20,21], and give rise to drag forces [22,23]. Under the influence of an electric field the ion velocity distribution may considerably differ from a displaced Maxwellian due to collisions with the neutral gas. Various phenomena related to the interaction between ions and dust particles have been shown to be crucially affected by the different dist...

Dynamic Behavior of Dust Particles in Plasmas

“…Our results have inspired other researchers in wider fields beyond plasma physics [64][65][66][67][68][69][70][71][72][73][74][75][76]. The followings are examples.…”

“…They reported that the turbulence was able to occur at a low Reynolds number if the Weissenberg number was high. Kähler et al derived the ion susceptibility in a partially ionized plasma [65]. Tadsen et al reported that the dust cloud confined in a magnetized plasma was diamagnetic [66].…”

Impact of collisions on the dust wake potential with Maxwellian and non-Maxwellian ions

“…We expect that our results will also be of direct relevance for experiments. Finally, an interesting question of current interest is how wake effects are modified in a magnetic field, where experiments 33 and linear response simulations 34,35 have observed a drastic modification of the wake potential with increasing field strength.…”

Suppression of the ion drag force on dust in magnetized plasmas

“…While the Coulomb interaction of dust with magnetised ions has been previously studied [13][14][15][16] , particularly in the context of wake effects, there are no known theoretical models by which the momentum transfer associated with this interaction may be calculated. However, the similar problem of Coulomb scattering of a point charge in strong magnetic fields has been treated in the context of ion stopping in a magnetised electron plasma, for which Nersisyan, Toepffer, and Zwicknagel have calculated the energy loss of a charge by treating its binary collision with another charge as a perturbation to its helical motion [17][18][19] .…”