A theoretical model for electromagnetic characterization of a spherical dust molecular cloud equilibrium structure (original) (raw)
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2012
We propose a new technique after the modified Lane-Emden equation to explore the electromagnetic properties of spherically symmetric dust molecular cloud (DMC) in field-free hydroelectrostatic equilibrium. Its subsequent characterization on the Jeans scale is made analytically and numerically. The lowest order cloud surface boundary (CSB) by the electric field maximization, E 6 0:15T=ek J ¼ 4:85 Â 10 À7 V m À1 , lies at a radial distance n = 3.50k J = 1.08 Â 10 9 m. The basic physics of the CSB formation is explored. It is interestingly observed that the CSB is biased with electrostatic potential h $ À0.34T/e (=À340 V) due to plasma boundary wall interaction, and plasma sheath-sheath coupling processes because sheath exists with each dust grain in plasma background. The net CSB charge comes out as Q $ À6.83 Â 10 À1 C. The major results are found to be in qualitative agreement with the existing models. Main conclusions of astrophysical importance and future applicability are briefly presented.
Equilibrium configuration of self-gravitating charged dust clouds: Particle approach
Physics of Plasmas, 2019
A three dimensional Molecular Dynamics (MD) simulation is carried out to explore the equilibrium configurations of charged dust particles. These equilibrium configurations are of astrophysical significance for the conditions of molecular clouds and the interstellar medium. The interaction among the dust grains is modeled by Yukawa repulsion and gravitational attraction. The spherically symmetric equilibria are constructed which are characterized by three parameters: (i) the number of particles in the cloud, (ii) Γg (defined in the text) where Γg−1 is the short range cutoff of the interparticle potential, and (iii) the temperature of the grains. The effects of these parameters on dust cloud are investigated using a radial density profile. The problem of equilibrium is also formulated in the mean field limit where total dust pressure, which is the sum of kinetic pressure and the electrostatic pressure, balances the self-gravity. The mean field solutions agree well with the results of ...
Plasma Science and Technology, 2014
This paper adopts an inertia-centric evolutionary model to study the excitation mechanism of new gravito-electrostatic eigenmode structures in a one-dimensional (1-D) planar self-gravitating dust molecular cloud (DMC) on the Jeans scale. A quasi-neutral multi-fluid consisting of warm electrons, warm ions, neutral gas and identical inertial cold dust grains with partial ionization is considered. The grain-charge is assumed not to vary at the fluctuation evolution time scale. The neutral gas particles form the background, which is weakly coupled with the collapsing grainy plasma mass. The gravitational decoupling of the background neutral particles is justifiable for a higher inertial mass of the grains with higher neutral population density so that the Jeans mode frequency becomes reasonably large. Its physical basis is the Jeans assumption of a self-gravitating uniform medium adopted for fiducially analytical simplification by neglecting the zero-order field. So, the equilibrium is justifiably treated initially as "homogeneous". The efficacious inertial role of the thermal species amidst weak collisions of the neutral-charged grains is taken into account. A standard multiscale technique over the gravito-electrostatic equilibrium yields a unique pair of Korteweg-de Vries (KdV) equations. It is integrated numerically by the fourth-order Runge-Kutta method with multi-parameter variation for exact shape analyses. Interestingly, the model is conducive for the propagation of new conservative solitary spectral patterns. Their basic physics, parametric features and unique characteristics are discussed. The results go qualitatively in good correspondence with the earlier observations made by others. Tentative applications relevant to space and astrophysical environments are concisely highlighted.
Communications in Physics, 2014
A theoretical evolutionary model for the nonlinear stability analysis of a planar dust molecular cloud (DMC) in quasi-neutral hydrodynamic equilibrium on the Jeans scales of space and time is developed. It is based on a self-gravitating multi-fluid model consisting of the warm electrons and ions, and the inertial cold dust grains with partial ionization. The Jeans assumption of self-gravitating uniform medium is adopted for fiducially analytical simplification by neglecting the zero-order field. So, the equilibrium is justifiably treated initially as “homogeneous”, thereby validating nonlinear local analysis. The lowest-order finite inertial correction of the thermal species (thermal inertia, which is conventionally neglected), heavier grain-charge fluctuation and all the possible collisional dynamics are included simultaneously amid non-equilibrium plasma inhomogeneities. We apply a standard multiple scaling technique methodologically to show that the eigenmodes are collectively go...
Astrophysics and Space Science
We formulate exact non-local linear analysis for identification and characterization of the global collective gravito-electrostatic eigenmodes, discrete oscillations and associated instabilities in interstellar charged dust molecular cloud (DMC) sphere with mass-radius above the stability critical values on the astrophysical fluid scales of space and time. The realistic relevant zeroth-order effects, hitherto remaining unaccounted for, are concurrently included. It avoids using any kind of the Jeansian swindles against usual viewpoint. Armed with the modified Fourier planewave method, the dispersion relations (eigenvalues) and amplitude-variations (eigenfunctions) of the relevant perturbations about the inhomogenous equilibrium are procedurally derived and analyzed together with numerical illustrations. It is seen that the entire cloud supports spectrally heterogeneous mixture of the Jeans (gravitational) and electrostatic (acoustic) modes, coupled via quasi-linear discrete oscillations of mixed pattern. The lowest-order nonrigid diffused cloud surface boundary (CSB), sourced by active gravito-electrostatic interplay, is the most unstable interfacial plasma layer. Three distinct and spatio-spectrally isolated classes of global eigenmodes-dispersive, nondispersive and hybrid types-are keyed together with idiosyncratic prolific features. Dispersive features are prominent in the ultra-high k-regime (acoustic) with modified form due to self-gravitational condensation of the Jeans modes; whereas, non-dispersive characteristics in the ultralow k-regime (gravitational) dominated by the Jeans waves; where, k = 2π/λ is the angular wave number of the fluctuations on the Jeans scale. We further demonstrate that the
First-principles simulations of electrostatic interactions between dust grains
Physics of Plasmas, 2014
We investigated the electrostatic interaction between two identical dust grains of an infinite mass immersed in homogeneous plasma by employing first-principles N-body simulations combined with the Ewald method. We specifically tested the possibility of an attractive force due to overlapping Debye spheres (ODSs), as was suggested by . Our simulation results demonstrate that the electrostatic interaction is repulsive and even stronger than the standard Yukawa potential. We showed that the measured electric field acting on the grain is highly consistent with a model electrostatic potential around a single isolated grain that takes into account a correction due to the orbital motion limited theory. Our result is qualitatively consistent with the counterargument suggested by , indicating the absence of the ODS attractive force.
Metrics of static spheroidal charged dust distributions
International Journal of Theoretical Physics, 1978
Two sets of solutions for a static incoherent charge distribution with spheroidal symmetry are presented. In one set, the charge distribution can be bounded and the charge-to-mass-density ratio is unity everywhere in relativistic units. In the other, the distribution pervades the entire space and the ratio of charge to mass-density also varies at different points.
Plasma Physics and Controlled Fusion, 2012
Nano and micro meter sized dust particles travelling through the heliosphere at several hundreds of km/s have been repeatedly detected by interplanetary spacecraft. When such fast moving dust particles hit a solid target in space, an expanding plasma cloud is formed through the vaporisation and ionisation of the dust particles itself and part of the target material at and near the impact point. Immediately after the impact the small and dense cloud is dominated by collisions and the expansion can be described by fluid equations. However, once the cloud has reached µm dimensions, the plasma may turn collisionless and a kinetic description is required to describe the subsequent expansion. In this paper we explore the late and possibly collisionless spherically symmetric unconstrained expansion of a single ionized ion-electron plasma using N-body simulations. Given the strong uncertainties concerning the early hydrodynamic expansion, we assume that at the time of the transition to the collisionless regime the cloud density and temperature are spatially uniform. We do also neglect the role of the ambient plasma. This is a reasonable assumption as long as the cloud density is substantially higher than the ambient plasma density. In the case of clouds generated by fast interplanetary dust grains hitting a solid target some 10 7 electrons and ions are liberated and the in vacuum approximation is acceptable up to meter order cloud dimensions. As such a cloud can be estimated to become collisionless when its radius has reached µm order dimensions, both the collisionless approximation and the in vacuum approximation are expected to hold during a long lasting phase as the cloud grows by a factor 10 6. With these assumptions, we find that the transition from the collisional to the collisionless regime could occur when the electron Debye length λ D within the cloud is much smaller than the cloud radius R 0 , i.e. Λ ≡ λ D /R 0 ≪ 1. This implies a quasi-neutral expansion regime where the radial electron and ion density profiles are equal through most of the cloud except at the cloud-vacuum interface. The consequence of Λ being much smaller that unity implies that the electrostatic fields within a cloud generated by a dust impact on a neutral target is ∼ 100 times weaker than in the case of grains hitting a spacecraft, where the positive potential of the target is strong enough to strip-off all the electrons from the expanding cloud leading to a "Coulomb explosion" like regime (e.g. Peano et al (2007) [1]).
Dust in the planetary system: Dust interactions in space plasmas of the solar system
Physics Reports, 2014
Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust.