Numerical simulations of a dust grain in a flowing magnetized plasma

Abstract

The effect of an external magnetic field on the formation of the wake in the potential distribution behind a dust grain is studied with selfconsistent Particle-In-Cell numerical simulations. The collisionless plasma flow is aligned with the magnetic field. It is demonstrated that the topology of the wakefield is significantly affected by the magnetization degree of plasma and by the ion flow speed. The external magnetic field acts to reduce the potential enhancements in the wake and leads to splitting of the wake pattern across the symmetry axis. For high ion flow speeds, a strong magnetization of plasma suppresses the potential enhancements and results in a narrow negative potential line along the symmetry axis, parallel to the ion flow direction, in the wake.

Electron Wing‐Like Structures Formed at a Negatively Charged Spacecraft Moving in a Magnetized Plasma

“…In a magnetized plasma, which is found at LEO, the electron dynamics are controlled by the magnetic field, and thus, the wake can be modified as compared to the unmagnetized case, and also become asymmetric (Darian et al, 2017;Usui et al, 2019). Note that an object in flowing plasmas is still one of outstanding problems of general interest in plasma physics, including complex plasmas, charging of solar system small bodies, or probe measurement techniques (Shukla & Mamun, 2002;Vladimirov et al, 2005;Holmström et al, 2012;Miyake & Nishino, 2015;Beadles et al, 2017;Darian et al, 2019).…”

A Novel Method for Circuits of Perfect Electric Conductors in Unstructured Particle-in-Cell Plasma–Object Interaction Simulations

“…Since the boundaries are open, plasma particles may leave the domain, and new particles from each species must be injected into the domain in accordance with the velocity distribution function of the ambient plasma. We note, however, that in some cases, such as a supersonic flow around an object, acceptable results are attained even when the velocity distribution is perturbed at the boundary [33]. Long extending perturbations of the wake in supersonic flows can lead to a local error at the downstream boundary, but it is being carried out of the domain with the flow and does not propagate upstream more than a few Debye lengths.…”

Suppression of the ion drag force on dust in magnetized plasmas

“…Particles are then injected at the upper and lower planes of the cylinder, and their trajectories are evaluated using a Boris integrator until they are either collected onto the dust grain surface, or they exit the simulation domain. The injected particle velocities are sampled 21 from a shifted-Maxwellian distribution, as is standard for dust-plasma interaction codes 15,[22][23][24] . The shifted-Maxwellian distribution is used in place of more realistic tokamak plasma distribution functions as it is simple to implement, and allows more direct comparison with existing models of charging and drag which generally assume this distribution.…”

“…A principle limitation of the DiMPl code in this work is the use of an assumed spherically symmetric potential with a fixed shielding length, rather than a potential profile that is evaluated self-consistently. This is less problematic in the tokamak plasma conditions we are considering than it would be in a discharge plasma with colder ions, where supersonic plasma flows result in significant perturbation to the shape of the potential 15,23,32 . Instead, when the ion and electron temperatures are comparable, the potential is less affected by flows, and PIC simulations of ion drag in the absence of a magnetic field show close agreement with the Khrapak model up to flow speeds several times the ion thermal speed 22 .…”