Scaling of plasma-body interactions in low Earth orbit

Abstract

This paper derives the generalised set of dimensionless parameters that scale the interaction of an unmagnetised multi-species plasma with an arbitrarily charged object - the application in this work being to the interaction of the ionosphere with Low Earth Orbiting (LEO) objects. We find that a plasma with K ion species can be described by 1+4K independent dimensionless parameters. These parameters govern the deflection and coupling of ion species k, the relative electrical shielding of the body, electron energy, and scaling of temporal effects. The general shielding length λϕ is introduced, which reduces to the Debye length in the high-temperature (weakly coupled) limit. The ability of the scaling parameters to predict the self-similar transformations of single and multi-species plasma interactions is demonstrated numerically using pdFOAM, an electrostatic Particle-in-Cell—Direct Simulation Monte Carlo code. The presented scaling relationships represent a significant generalisation of past work, linking low and high voltage plasma phenomena. Further, the presented parameters capture the scaling of multi-species plasmas with multiply charged ions, demonstrating previously unreported scaling relationship transformations. The implications of this work are not limited to LEO plasma-body interactions but apply to processes governed by the Vlasov-Maxwell equations and represent a framework upon which to incorporate the scaling of additional phenomena, e.g., magnetism and charging.

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

“…The importance of the sheath and wake effects for in-situ measurements has been recognized early, and a number of studies were carried out to address this problem with increasingly more realistic models and simulations (Wang & Hastings, 1992;Scime et al, 1994;Torkar et al, 1998;Engwall et al, 2006;Svenes & Trøim, 1994;Garrett & Whittlesey, 2000;Anderson, 2012;Marchand et al, 2014;Miyake & Usui, 2016;Marchand & Lira, 2017;Capon et al, 2017). Due to the computational complexity, only recently, the effects of the magnetic field on the wake and spacecraft charging have been studied in self-consistent simulations (Marchand, 2012;Darian et al, 2017).…”

Mixed flow ionospheric aerodynamics

“…1. Extend set of parameters in Capon et al [22] to account for multispecies interactions in the formulation of a control surface.…”

“…These systems are suited to explaining the response of a plasma to a disturbance, but fall short in describing the aerodynamic interactions of a plasma and a solid body. An alternative set of parameters for ionospheric aerodynamic analysis is given by Capon et al [22], summarised here.…”

“…In this region, ions are accelerated towards the body while electrons are repelled, resulting in an area of relatively low ion density, the thickness of which depends on the floating potential, as well as the ion distribution of the flow [21]. The structure of this plasma sheath, elaborated on more fully in Chapter 5, is crucial to the understanding of ionospheric aerodynamic interactions [22] with permission from author) [1], with several major distinctions from a traditional neutral flow. Most notably, the plasma sheath provides a larger effective collection area, with ions being accelerated towards the forebody that would otherwise not be in its path, and would not have contributed to drag forces (Fig.…”

“…Other Ion species are also present at these altitudes in lower numbers, leading to a flow containing a mixture of various ions, either dominated by O+ or the much lighter H+ species. While the latter assumption is not explicitly tested in [1], the C D of various plasma flows is shown to be very sensitive to small variations in wake structure, and the mixed species cases shown in [22] showed significantly altered wake structures, indicating the inclusion of a species of significantly different behaviour (specifically the charge-mass ratio) will likely provide a nonnegligible contribution to total drag . Work performed by Severn et al [2] in the form of laser flourescence measurements of a plasma sheath found the introduction of lighter He+ ion species to an existing Ar+ flow resulted in the Ar+ ions entering the sheath with an increased velocity, though the mechanism behind this was not explained in this work.…”