Existence of bulk acoustic modes in pair plasmas

Abstract

In view of applications to electron-positron and fullerene pair plasmas, a thorough discussion is given of the dispersion of linear electrostatic waves, before finding the parameter ranges in which stationary nonlinear electrostatic modes can exist, when there is a thermodynamic asymmetry between both constituents. Arguments for such an asymmetry can be found in the observed dispersion in fullerene pair plasma experiments, but point to small asymmetries. The existence of solitary modes is first discussed in general terms for various polytropic pressure-density relations, showing that the solitons are always compressive in both pair components. For large thermal asymmetries, there is at most a doubling of the densities, but small asymmetries lead to weakly nonlinear amplitudes, described by familiar Korteweg-de Vries solitons. Observations of an intermediate wave in the theoretical gap between the acoustic and Langmuir branches of the linear dispersion diagram might be accounted for, at least partially, by a train of weak solitons, as the difference between weak solitary modes and linear harmonic waves is rather difficult to ascertain experimentally.

Exact relativistic plasma waves in an electron–positron plasma

“…Of particular relevance are the relatively long-lasting nonlinear electrostatic structures such as large-amplitude quasistationary waves, solitons, double layers, and shocks. Quasilinear and nonlinear waves in electron-positron plasmas have been much investigated (Stenflo and Tsintsadze 1979;Chian and Kennel 1983;Yu et al 1984, 1986, Stenflo et al 1985Shukla et al 1986a;1986b;Bharuthram and Yu 1993;Popel et al 1995;Zank and Greaves 1995;Machabeli et al 2002;Mahmood et al 2003;Verheest 2006;Luo and Melrose 2008;Liu et al 2008;Alinejad 2009). Most investigations are based on perturbations or interactions of the corresponding linear eigenmodes, so that the resulting waves have similar physical properties to the latter.…”

Nonlinear Dynamics of Rotating Multi-Component Pair Plasmas and e-p-i Plasmas

“…Two of these modes, namely an acoustic mode and a Langmuir-like high-frequency mode, are predicted by theory [1,2,10,11]. An intermediatefrequency mode also reported [5] is still a topic of controversial debate among theoreticians, and various alternative interpretations have been furnished, in terms of solitontrains [12], ion acoustic waves accelerated by surplus electrons [13] or BernsteinGreeneKruskal (BGK)-like trapped ion modes [14]. Although, the experiments mentioned above rely on a symmetric pair-component plasma preparation ("pure" p.p., i.e.…”

“…Nonlinear excitations predicted to occur in pair plasmas and e-p-i plasmas include ES solitons [12,15], EM solitons [16] and localized-envelope modulated wavepackets (envelope solitons) of either low-frequency ES [10,11], high-frequency ES [17] or EM [18] type, relying on an exhaustive use of the nonlinear plasma toolbox, including the Korteweg -de Vries (KdV) and Zakharov-Kuznetsov (ZK) Equation(s), the Sagdeev pseudopotential formalism and the nonlinear Schrödinger (NLS) Equation, respectively.…”

Shear flow-driven electrostatic instabilities in low density and low temperature pair-ion plasmas with and without electrons

“…Some authors have expressed their doubts about these observations. [11][12][13][14] It has been pointed out by one of the present authors 15 that the produced pair-ion fullerene plasma contains electrons as well and it is important to invent some technique to measure the electron density in a PI plasma. A theoretical criterion to define the system as a pure PI plasma has also been presented in this work.…”