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Coupling of charged particles via Coulombic interactions: Numerical simulations and resultant kappa‐like velocity space distribution functions
Author(s) -
Randol Brent M.,
Christian Eric R.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021859
Subject(s) - physics , coupling (piping) , distribution function , coupling parameter , plasma , atomic physics , distribution (mathematics) , range (aeronautics) , space (punctuation) , charged particle , acceleration , parameter space , thermal velocity , classical mechanics , quantum mechanics , ion , mechanics , flow velocity , materials science , statistics , mathematical analysis , linguistics , philosophy , mathematics , flow (mathematics) , metallurgy , composite material
A parametric study is performed using the electrostatic simulations of Randol and Christian ([Randol, B. M., 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 of v , 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 ([Randol, B. M., 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.