Electron acoustic nonlinear structures in planetary magnetospheres

Abstract

In this paper, we have studied linear and nonlinear propagation of electron acoustic waves (EAWs) comprising cold and hot populations in which the ions form the neutralizing background. The hot electrons have been assumed to follow the generalized (r,q) distribution which has the advantage that it mimics most of the distribution functions observed in space plasmas. Interestingly, it has been found that unlike Maxwellian and kappa distributions, the electron acoustic waves admit not only rarefactive structures but also allow the formation of compressive solitary structures for generalized (r,q) distribution. It has been found that the flatness parameter r, tail parameter q, and the nonlinear propagation velocity u affect the propagation characteristics of nonlinear EAWs. Using the plasmas parameters, typically found in Saturn's magnetosphere and the Earth's auroral region, where two populations of electrons and electron acoustic solitary waves (EASWs) have been observed, we have given an estimate of the scale lengths over which these nonlinear waves are expected to form and how the size of these structures would vary with the change in the shape of the distribution function and with the change of the plasma parameters.

An alternative explanation for the density depletions observed by Freja and Viking satellites

“…16,18,25 These nonthermal distributions significantly deviate from the classical Maxwellian distribution function and have successfully been employed to investigate different kinds of phenomena in realistic environments. 13,14,16,17,[26][27][28] In this paper, we use generalized (r,q) distribution function to study the nonlinear ion-acoustic waves which has the following standard three-dimensional form 18 f rq (…”

Investigation of cubic non‐linearity‐driven electrostatic structures in the presence of double spectral index distribution function

“…Whenever particle distribution has an abundance of superthermal particles, it is modelled in a better fashion by employing kappa distribution function. [36] This aspect could not be investigated by distributions containing high-energy tails only. Tahir et al [25] employed bi-product (r, q) distribution for adiabatically trapped electrons to study obliquely propagating Alfven waves.…”

Ion‐acoustic solitary waves in e‐p‐i plasmas with (r, q)‐distributed electrons and kappa‐distributed positrons

“…Electrons are assumed to follow the (r, q) distribution function for which the total electron density can be written as [22,36] n e = (1 +…”

“…Several studies on non-Maxwellian plasmas have shown that wave characteristics change significantly due to the presence of non-thermal distributions and provided a better insight into the underlying physical processes. [22][23][24][25][26] Kappa distribution has been used extensively to study various electrostatic and electromagnetic non-linear waves in astrophysical and space plasmas and is characterized by the spectral index , which basically models the particles with velocities greater than the thermal velocity. A smaller value of signifies a larger number of high-energy particles in the distribution and vice versa.…”