Cold Ion Species Research Articles

Arbitrary amplitude ion-acoustic supersolitons in negative ion plasmas with two-temperature superthermal electrons

Arbitrary amplitude ion-acoustic supersolitons are investigated with two-temperature superthermal electrons in an unmagnetized negative ion plasma. In this study, we have considered the plasma containing two cold ion species with different masses, ion concentration and charge multiplicity, and two superthermal (non-Maxwellian) electrons. The energy integral equation has been derived by using the Sagdeev pseudopotential technique. We have investigated that both negative and positive potential supersolitons and solitons can exist in the selected domain of Mach number. A numerical analysis shows that the ion-acoustic supersolitons appear below the acoustic speed (Ms). The amplitude of the supersoliton is found larger than the soliton. The formation of solitons and supersolitons (both polarity) is analyzed by phase portrait of the dynamic of the plasma system. The plasma system also supports the coexistence of compressive and rarefactive solitons for a particular set of plasma parameters. The present study is focused on ion-acoustic solitary and supersolitary waves in the D-and F-regime of Earth's ionosphere and experimentally produced plasmas (Ar+, F−) and (Ar+, SF−6) ion species. The present investigation may be helpful in understanding the nonlinear behavior of supersoliton and soliton in space and laboratory plasmas, where negative ions are present with superthermal electrons at two temperatures.

Bright and dark envelope solitons in negative-ion plasmas in the presence of Maxwellian electrons population

Using the Krylov–Bogoliubov–Mitropolsky (KBM) perturbation method, a nonlinear Schrödinger (NLS) equation describing the slow modulation of the wave amplitude of the ion-acoustic wave is derived for the system. We have considered a collisionless plasma consisting of two cold-ion species with different masses, concentrations, and charge states and hot-isothermal electrons. The steady state solution of the nonlinear Schrödinger (NLS) equation is also discussed, which support bright and dark envelope solitons. The conditions for the existence of two types of localized envelope (Bright/dark) structures are investigated in terms of relevant parameters. We have discussed the characteristic of bright and dark envelope solitons in three plasmas compositions with (H+, O2−), (H+, H−), and (Ar+, F−). The dispersive and nonlinearity coefficients are obtained in terms of various plasma parameters. The range of parameters is investigated numerically in which system supports bright/-dark envelope solitons, and it is shown that envelope solitons exist in negative-ion plasma. The finding of the present study may be useful to understand some aspects of bright/dark envelope solitary waves in astrophysical negative-ion plasmas.

MMS Measurements and Modeling of Peculiar Electromagnetic Ion Cyclotron Waves

AbstractOrbiting Earth's dayside outer magnetosphere on 29 September 2015, the Magnetospheric Multiscale (MMS) satellites measured plasma composition, simultaneous electromagnetic ion cyclotron waves, and intermittent fast plasma flows consistent with ultralow frequency waves or convection. Such flows can accelerate typically unobservable low‐energy plasma into a measurable energy range of spacecraft plasma instrumentation. We exploit the flow occurrence to ensure measurement of cold ion species alongside the hot particles—consisting of ionospheric heavy ions and solar wind He++—during a subinterval of wave emissions with spectral properties previously described as peculiar. Through application of the composition and multisatellite wave vector data to linear theory, we demonstrate the emissions are in fact consistent with theory, growing naturally in the He++ band with sufficient free energy.

THEMIS observations and modeling of multiple ion species and EMIC waves: Implications for a vanishing He+ stop band

Observations of left‐hand polarized electro‐magnetic ion cyclotron (EMIC) waves with significant wave power across fHe+ are presented. Concurrent field and particle measurements reveal pitch angle scattering of thermal ions during the interval of maximum wave power. The observations suggest the presence of multiple cold ion species (H+, He+) at this time, below the sum of spacecraft potential and minimum energy of the ion instrument (i.e., <∼20 eV). Fortuitously, immediately following the most intense wave activity, the ambient plasma flow velocity became sufficiently large such that cold ions can be accelerated into the energy range of the particle instrument. Thus, two low energy ion components are revealed in the particle measurements at energies consistent with cold protons and He+. Maxwellian fits provide approximations of these cold ion species component densities and temperatures. The linear dispersion relation of parallel propagating EMIC waves for the observed conditions shows a vanishing cold plasma He+ stop band, consistent with the wave measurements during this interval. These results provide the first observational evidence of the importance of the cool ion species temperature/density in controlling linear wave growth through the heavy ion stop bands in warm plasma theory.

Effect of negative ions on filamentation instability in collisionless three-fluid theory of plasmas with cold ion species

The growth rate of filamentation is examined analytically, as a function of the number density and the particle mass of negative ions, in the collisionless three-fluid theory of a plasma with cold ions. The growth rate dependence on the number density shows a qualitative change according to whether the pump intensity is below or above a critical level. In all cases of the pump intensity, the higher particle mass of negative ions means the weaker growth of filamentation.

Stability of oblique modulation of ion-acoustic waves in a multicomponent plasma

The stability of oblique modulation of ion-acoustic waves in a collisionless plasma consisting of two cold-ion species with different masses, concentrations, and charge states, and hot isothermal electrons is studied. Using the Krylov–Bogoliubov–Mitropolosky (KBM) perturbation technique, a nonlinear Schrödinger equation governing the slow modulation of the wave amplitude, is derived for the system. It is found that the presence of second-ion species significantly changes the instability domain in the k-φ plane. The effect of charge state, concentration, and mass of second-ion species on the modulational instability is discussed in detail. The predictions of the theory are found to be in good agreement with the experimental observations.

Study of ion-acoustic rarefactive soliton in a two-electron temperature plasma

The propagation characteristics of ion-acoustic rarefactive soliton (IARS) in a two-electron temperature plasma with two cold ion species are investigated considering the nonisothermal distributions of electrons using a kinetic model and fluid model for both ion species. Using the Sagdeev potential formalism the nonlinear dispersion relation and expression for width are derived for IARS. The variation of Mach number and width of the IARS with the amplitude is studied numerically and compared with earlier theoretical results as well as experimental observations. It is found that the results are improved qualitatively as well as quantitatively with the consideration of the presence of a suitable negative ion-impurity.

Ion acoustic double layers and solitons in auroral plasma

Small amplitude ion acoustic double layers and solitons were studied in an auroral plasma consisting of hot and cold electrons and two cold ion species (e.g. oxygen-hydrogen). For the auroral plasma parameters, the analysis predicts either rarefactive double layers or rarefactive solitons or compressive solitons existing in distinct parametric space (N H, T H T C ) , where N H is a relative density of hot electrons and T H, C represents the temperature of hot (cold) electron population. An increase in the oxygen number density reduces the parametric region of rarefactive double layers and at the same time pushes it towards the higher N H values. Both the width (half width) of the double layer (solitons) and their velocities as predicted by the theory, assuming relative oxygen density of 0.2–0.8, are in good agreement with the observed values from the S3-3 and the Viking satellite data.

Large-amplitude ion-acoustic double layers in multispecies plasma

We have investigated the effect of second-ion species on the characteristics of a large-amplitude ion-acoustic double layers (IADL) in a collisionless, unmagnetized plasma consisting of hot and cold Maxwellian populations of electrons and two cold-ion species with different masses, concentrations, and charge states. After deriving the criteria for the existence of large-amplitude IADL, we find that the presence of a positive-ion impurity does not modify considerably the characteristics of large-amplitude IADL. However, the presence of a negative-ion impurity changes significantly the characteristics of large-amplitude IADL. We have also presented an analytic discussion of small-amplitude IADL using a reductive perturbation method.

A quiver-kinetic formulation of radio-frequency heating and confinement in collisional edge plasmas

The near fields in the collisional edge plasma of a radio-frequency-heated tokamak can cause one or more charged species to oscillate in the applied field with a quiver (or jitter) speed comparable to its thermal speed. By assuming the quiver motion dominates over drifts and gyromotion a completely new kinetic description of the flows in an edge plasma is formulated that retains Coulomb collisions and the relevant atomic processes. Moment equations are employed to obtain a description in which only a lowest-order quiver-kinetic equation need be solved to evaluate the slow time particle fluxes and current induced by the applied fields. The electron heating by collisional randomization of their quiver motion (inverse bremsstrahlung) is balanced by impact excitation losses since equilibration with the ions is too weak. A model plasma of electrons, neutrals, and a single cold ion species is considered to illustrate the utility of the quiver-kinetic formulation. The model predicts local electrostatic potential changes and a local E×B convective flux that is of the same magnitude and scaling as would be predicted by Bohm diffusion.

Arbitrary-amplitude rarefactive ion-acoustic double layers in warm multi-fluid plasmas

Large- and small-amplitude rarefactive ion-acoustic double layers have recently been studied in a fluid plasma with double Maxwellian electrons and a single cold ion species. Here the stationary large-amplitude theory is generalized to include two warm ion species. A technique for numerically solving the full nonlinear problem is presented. With it, useful predictions of the effect of ion temperatures and of light-ion contamination on the double-layer structure are made. A generalization to an arbitrary number of similar fluid components is pointed out. The small-amplitude perturbation theory is also extended to such a plasma, and in its restricted regime good qualitative agreement is obtained with the results of the large-amplitude theory.

Modulation instability of ion-acoustic waves in a multi-ion plasma

Abstract A nonlinear Schrodinger equation for ion-acoustic waves in a collision-free plasma, consisting of a mixture of two cold ion species and hot isothermal electrons is derived using the KBM method. It is used to discuss the modulation instability in which the effect of the light-on concentration is analysed. We find that the unstable region depends sensitively upon the fraction of light-ion concentration (α) and the ion-mass ratio. An approximate relation for α critical is derived for a given ion species in terms of the ion-mass ratio, which governs the minimum wave number, below which the carrier wave is stable against the modulational instability.

Ion-acoustic solutions and shock waves in multicomponent plasmas

The present investigation of ion-acoustic waves is based on the study of the nonlinearity of plasma waves in a dispersive medium. Here the authors study ion-acoustic solitary waves in a warm ion plasma with non-isothermal electrons and then the results for solitary waves in a plasma with isothermal electrons are obtained. Incorporating the previous results obtained from the solitary wave solutions, the authors generalize the effect of negative ions on ion-acoustic waves in plasmas consisting of either a warm or cold ion species. A reflection phenomenon of ions in these waves is also studied. These results can be generalized, but the discussion is limited to a particular model of the plasma.

Stabilization of Drift-Cyclotron Loss-Cone Mode by Low-Frequency Density Fluctuations

Low-frequency ($\ensuremath{\omega}\ensuremath{\ll}{\ensuremath{\omega}}_{\mathrm{ci}}$) density fluctuations (which may be produced by the drift-wave instability of the cold-ion species) can stabilize the drift-cyclotron loss-cone (DCLC) mode by scattering electrons and thereby providing anomalous high-frequency resistivity to the DCLC mode.

High-Energy Ion Expansion in Laser-Plasma Interactions

Measurements of energetic-ion energy distributions produced from C${\mathrm{D}}_{2}$ and C${\mathrm{H}}_{2}$ targets are compared with a numerical model. The model describes the ambipolar expansion of hot electrons and two relatively cold ion species from an electron pressure gradient. For C${\mathrm{D}}_{2}$ the plasma expansion is adequately represented by a single ion species, whereas for C${\mathrm{H}}_{2}$ two-ion fluids are required to account for the energy and the relative behavior of the high-energy ion species.