Electrostatic ion waves in non-Maxwellian pair-ion plasmas (original) (raw)

The electrostatic ion waves are studied for non-Maxwellian or Lorentzian distributed unmagnetized pair-ion plasmas. The Vlasov equation is solved and damping rates are calculated for electrostatic waves in Lorentzian pair-ion plasmas. The damping rates of the electrostatic ion waves are studied for the equal and different ion temperatures of pair-ion species. It is found that the Landau damping rate of the ion plasma wave is increased in Lorentzian plasmas in comparison with Maxwellian pair-ion plasmas. The numerical results are also presented for illustration by taking into account the parameters reported in fullerene pair-ion plasma experiments. During this decade, theoretical study of pair-ion PI plasma has gained attraction due to stable production of fullerene ion plasmas in the laboratory experiments. 1–3 The dynamics of symmetric or PI plasma is different from the usual electron-ion plasma in which both fast and slow time scales occur due to difference in masses of ions and electrons. The collective behavior of fullerene PI plasmas has also been studied and three types of electrostatic waves, i.e., ion acoustic wave IAW, intermediate frequency wave IFW, and ion plasma wave IPW have been observed in the direction parallel to the magnetic field. The observed frequency ranges for IAW, IFW, and IPW are / 2 12 kHz, 12 / 2 20 kHz, and / 2 20 kHz, respectively , and the ion cyclotron frequency is c / 2 = 4.3 kHz at B = 0.2 T. A lot of theoretical research work has already been published on linear and nonlinear electrostatic waves in PI plasmas. Mostly two fluid plasma theory is used to study the dynamics of PI plasmas. 4–14 In PI plasmas, IPW and IAW can be derived from linear theory of two fluid plasma dynamics provided the temperature difference between the same mass ion species exist. In the experiments, it has been reported that a difference in temperature exists between two fullerene ion species which occurs due to different charging processes, i.e., the electron impact ionization and attachment for the production of both positive and negative of fullerene ions in PI plasmas. 2 The third mode IFW cannot be obtained from linear theory using two fluid model in homogeneous PI plasmas 2,7 and its theoretical understanding is still not clear. The surface ion waves in PI plasmas has been studied by Hasegawa and Shukla. 4 Schamel and Luque 15 investigated electrostatic waves in PI plasmas with the inclusion of trapped ions in the potential troughs in their model. Recently, the arbitrary amplitude solitary waves in PI plasma have been study by Dubinov et al. 8 They studied that elec-trostatic solitary waves are formed only when there exist a small difference of temperatures between PI species. The low amplitude solitons and shocks have been studied in PI plasma using reductive perturbation method. 10–12 It has been reported the nonlinear compressive and rarefactive electro-static structures are formed only when a little difference of temperature occurs between the PI species. Recently, a criterion for pure PI has been studied for its production in laboratory experiments. 16 The electrostatic modes parallel to magnetic field in PI plasmas have been studied by Vranjes and Poedts 17 for same temperature PI species. They studied the resonant damping of longitudinal electrostatic waves in PI plasma using the kinetic model for Maxwellian distributed PI plasmas. However , it has been mentioned by the authors that the choice of Maxwellian plasmas in their study is not a good assumption because ions collected from the exciter hole may not have completely followed the Maxwellian distribution in PI fullerene plasma experiment. 2 The non-Maxwellian velocity distributed plasmas have been observed in space and as-trophysical plasma situations. The observed particles are found to have distribution of quasi-Maxwellian up to mean thermal velocities with non-Maxwellian suprathermal tails at high velocities and energies. 18 The nonthermal plasmas are found to exist in the magnetospheres of the Earth and in planets and also in the solar wind. 19–21 In general, the observed non-Maxwellian plasma distributed particles are well fitted with the generalized Lorentzian or kappa distribution, which contains both thermal as well as suprathermal parts of the observed velocity spectra. The kappa distributions have been used by a number of authors to study the damping rates of the electrostatic and electromagnetic waves in plasmas. Therefore, it will be interesting to study longitudinal waves in PI plasma with kappa distribution function, so that the PI species are assumed to be nonthermal in the laboratory experiment. The kappa distribution function approaches to Maxwellian when the spectral index kappa approaches to infinity. Recently, the damping rate for Langmuir, dust ion acoustic, and dust acoustic waves are studied in generalized Lorentzian multicomponent plasmas. 22,23 In this brief communication, we study the electrostatic longitudinal waves in the presence of non-Maxwellian distributed generalized Lorentzian or kappa distribution pure PI plasma containing positive and negative fullerene C 60