Coupling of charged particles via Coulombic interactions: Numerical simulations and resultant kappa‐like velocity space distribution functions. Issue 3 (25th March 2016)

• Record Type: Journal Article
• Authors: Randol, Brent M.; Christian, Eric R.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 3(2016:Mar.)
• Page Start: 1907
• Page End: 1919
• Publication Date: 2016-03-25
• Subjects: plasma coupling -- Coulomb force -- electrostatic simulation -- nonextensive statistical mechanics -- N‐body problem -- suprathermal tail; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2015JA021859
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: A parametric study is performed using the electrostatic simulations of Randol and Christian (2014 ) in which the number density, n, and initial thermal speed, θ, are varied. The range of parameters covers an extremely broad plasma regime, all the way from the very weak coupling of space plasmas to the very strong coupling of solid plasmas. The first result is that simulations at the same Γ D, where Γ D ( ∝ n 1/3 θ −2 ) is the plasma coupling parameter, but at different combinations of n and θ, behave exactly the same. As a function of Γ D, the form of p ( v ), the velocity distribution function of v, the magnitude ofv, the velocity vector, is studied. For intermediate to high Γ D, heating is observed in p ( v ) that obeys conservation of energy, and a suprathermal tail is formed, with a spectral index that depends on Γ D . For strong coupling ( Γ D ≫1), the form of the tail is v −5, consistent with the findings of Randol and Christian (2014 ). For weak coupling ( Γ D ≪1), no acceleration or heating occurs, as there is no free energy. The dependence on N, the number of particles in the simulation, is also explored. There is a subtle dependence in the index of the tail, such that v −5 appears to be the N → ∞ limit. Key Points: Results depend only on ratio of average initial potential energy to average initial kinetic energy Resulting velocity distribution function is kappa‐like, with a high‐energy tail Tail index depends directly on ratio of energies and ‐5 index is the high potential energy limit