General formulation for acoustic solitons in three-component nonthermal plasmas

Abstract

A generalized formulation is developed for nonlinear acoustic solitons in three-component such as dust-ion-electron and electron-positron-ion plasmas with the charge of each species being unspecified. The heavy, cold charged particles (ions or dust particles) are treated as a fluid while the light, hot components are described by the kinetic Vlasov equation with separate velocity distributions which can be of j function or highly nonthermal (non-monotonic) distributions. The model is also applicable for two-component such as ion-electron plasmas with two different temperatures for electrons. The generalized dispersion relation for acoustic waves and the Korteweg-de Vries equations as well as the Sagdeev potential are derived for various models with different combinations of velocity distributions. The parameter regimes for the existence of acoustic solitons are analyzed and examples of nonlinear solutions are illustrated. The polarity of electric potential is found to exhibit anomaly for highly nonthermal cases.

Fluid aspects of electron streaming instability in electron-ion plasmas

“…In particular, steady solutions for ion acoustic solitons in association with the electron hole are constructed based on solving time stationary kinetic equations for hot electrons and fluid equations for cold ions. 32 The resulting governing equation has the form of ðd/=dxÞ 2 =2 þ Vð/Þ ¼ 0 for which / is the electric potential and Vð/Þ is the Sagdeev's potential which can be solved numerically to obtain the soliton solutions. The characteristics of electrostatic acoustic solitons in thermal and nonthermal plasmas are shown to resemble some typical or anomalous features of the observed ESW.…”

General formulation for electrostatic solitons in multicomponent nonthermal plasmas

“…Note that both Cairns et al and the highly nonthermal distributions may describe nonmonotonic and bump-on-tail velocity distributions tonic kappa distribution, and may suitably be termed as the highly nonthermal distribution in the present study. As shown in figure 1, the features for both distributions are not quantitatively the same; in particular, the high tail peak may possibly exceed the central distribution in the Cairns et al case, which is not considered in our previous study for three-component plasmas [42]. The combination of both distributions may give rise to more generalized functions which may flexibly be fitted with the observations or simulations by suitably adjusting the free parameters in equation (6).…”

“…In light of the observational evidence for the existence of multiple components in space plasma environments [5][6][7][8][9], a number of theoretical models for electrostatic solitons in four-component plasmas have been developed [43][44][45][46]. In the present study we extend the formulations of Chuang and Hau [25,42] and Chuang [47] to more general cases with multiple (unlimited) hot components described by the combination of the kappa function and the more general nonthermal distribution function of…”

“…All three types of nonthermal distributions may suitably describe the various velocity distributions of nonthermal electrons observed in space plasma environments [10][11][12][13][14][15][16]41]. Chuang and Hau [42] have developed a general formulation for acoustic solitons in three-component plasmas consisting of one cold fluid and two hot components described by the combination of the kappa function and the highly nonthermal distribution function. In their study the charge of each component is a free parameter while the charge neutrality for background plasmas is imposed.…”

“…Note that for multiple components defined in equation (18) differs from the earlier studies and has the advantage of yielding physically meaningful C S,eff and λ D,eff which will be used as the normalization constants in the following calculations. The correct definition for the effective temperature in equation ( 18) and the corresponding sound speed is important in that the model calculations would not then yield subsonic solitons as obtained in earlier studies [25,30,42,57] which are not physically possible, since steady solitons require the balance between nonlinear steepening and dispersive effects in collisionless plasmas.…”