Electrostatic wave breaking limit in a cold electronegative plasma with non-Maxwellian electrons

Abstract

A one-dimensional multifluid hydrodynamic model has been adopted as basis for an investigation of the role of suprathermal electrons on the wave breaking amplitude limit for electrostatic excitations propagating in an electronegative plasma. A three-component plasma is considered, consisting of two inertial cold ion populations of opposite signs, evolving against a uniform background of (non-Maxwellian) electrons. A kappa-type (non-Maxwellian) distribution function is adopted for the electrons. By employing a traveling wave approximation, the first integral for the fluid-dynamical system has been derived, in the form of a pseudo-energy balance equation, and analyzed. The effect of intrinsic plasma parameters (namely the ion density ratio, the ion mass ratio, and the superthermal index of the nonthermal electrons) on the wave breaking amplitude limit is explored, by analyzing the phase space topology of the associated pseudopotential function. Our results are relevant to particle acceleration in Space environments and to recent experiments based on plasma-based accelerator schemes, where the simultaneous presence of negative ions and nonthermal electrons may be observed.

Wave breaking field of relativistically intense electrostatic waves in electronegative plasma with super-thermal electrons

“…Figure 6 shows the effect of various input parameters on the wave breaking limit, for fixed values of other parameters. From the top left panel we see that, the wave breaking field essentially increases with the concentration of negative ion species which also happens for nonrelativistic electronegative plasma case 39 and electron-ion-positron plasma case 33 . In Ref.…”

“…In the above equation is the density of the electrons and now we need an expression for the number density of the electrons as a function of the potential , which is usually evaluated by considering a distribution for the velocities of the electron species. A standard approach 39 is to take this situation into account by adopting a so-called distribution function, having the following form 38 where, is the equilibrium electron density and represents the spectral index of distribution and in the limit the above distribution becomes a standard Maxwellian distribution. represents the most probable speed which is essentially related to the thermal speed ( ) via the following relation: .…”

“…But it doesn’t affect the potential on the opposite side i.e. on the negative side of the potential 39 . Here also this asymmetry is caused by the power-law dependence of electron density with .…”

“…Very recently (in 2021), an analytical expression for the wave breaking amplitude of nonlinear electrostatic waves, in a electronegative plasma (where heavier negative ions are present), in the presence of Kappa ( )-distributed 38 electrons has been reported by Elkamash et al 39 . It has been theoretically found that the presence of negative ion-species enhances the wave breaking amplitude [Figure 2.…”

“…(b) in Ref. 39 ]. Naturally, these results are highly relevant to particle acceleration in plasma based accelerators and also in the space environment, where multi-ion species plasmas are regularly encountered 40 , 41 .…”