Cold Electron Number Density Research Articles

Ion-acoustic rogue waves in a multi-component plasma medium

The nonlinear propagation of ion-acoustic (IA) waves (IAWs) in a four component plasma medium (FCPM) containing inertial warm positive ions, and inertialess isothermal cold electrons as well as non-extensive (q-distributed) hot electrons and positrons is theoretically investigated. A nonlinear Schrödinger equation (NLSE) is derived by using the reductive perturbation method, and it is observed that the FCPM under consideration supports both modulationally stable and unstable parametric regimes which are determined by the sign of the dispersive and nonlinear coefficients of NLSE. The numerical analysis has shown that the maximum value of the growth rate decreases with the increase in q (q>1), and the modulationally unstable parametric regime allows to generate highly energetic IA rogue waves (IARWs), and the amplitude and width of the IARWs increase with an increase in the value of hot electron number density while decrease with an increase in the value of cold electron number density. The applications of our investigation in understanding the basic features of nonlinear electrostatic perturbations in many space plasma environments and laboratory devices are briefly discussed.

Background Parameter Effects on Linear–Nonlinear Chorus Wave Growth in the Planetary Magnetosphere

Abstract We investigate the effects of the background dipole magnetic field and cold electron number density on the linear and nonlinear growth of whistler-mode chorus waves for a region of relatively small anisotropy (A T ) in Saturn’s inner magnetosphere. The linear and nonlinear features of wave growth rate and associated frequency at L = 6 are presented in detail. Although a large anisotropy is generally in favor of linear and nonlinear wave growth, the nonlinear wave growth for a small anisotropy can still be generated. All cases show a small threshold for wave amplitudes , which compromises the requirement to trigger the nonlinear wave growth, but the comparisons also clearly indicate the important transition process from the linear phase to the nonlinear phase. After checking the variation of the calculation time steps depending on the chosen electron number density N c and background magnetic field B c , respectively, a large N c can promote the nonlinear wave growth, but a large B c works against it. Our results present how these parameters really affect the generations of linear and nonlinear wave growth quantitatively. This could be significant to further understand the monumental importance of whistler-mode chorus waves and the corresponding wave–particle interactions in the planetary magnetosphere.

Dependence of Whistler Mode Chorus Wave Generation on the Maximum Linear Growth Rate

AbstractWhistler mode chorus waves play a key role in controlling electron dynamics in Earth's inner magnetosphere. A criterion has been previously suggested whereby if the maximum value of the linear growth rate of whistler mode waves exceeds a certain critical bound, then fully nonlinear wave growth occurs and chorus waves are generated. This criterion corresponds to a boundary curve in (Nh/N0,AT) space where Nh is the hot electron number density, N0 is the cold electron number density, and AT is the thermal anisotropy. Chorus waves are generated in the region above the boundary curve, while no chorus waves are generated below the boundary curve. In the present study, we make use of a recently published set of 36 particle simulations of chorus, and we thereby are able to confirm the validity of the criterion. It is expected that this simple concept of the theoretical boundary curve based on linear theory will be useful in guiding the choice of parameters in future simulations of chorus and also of practical use in interpreting experimental chorus wave data.

Statistical Analysis on Plasmatrough Exohiss Waves From the Van Allen Probes

AbstractIn this study using Van Allen Probe wave observations we investigate the statistical properties of exohiss waves, which are structureless whistler mode waves observed outside the plasmapause. The exohiss waves are identified based on the cold electron number density, frequency distribution, ellipticity, and wave normal angle. The statistical analysis on exohiss wave properties shows that exohiss waves prefer to occur over 3<L<6 from dawnside to noon and duskside during geomagnetic quiet times, and their wave power is larger at smaller values of L shell. The frequency of exohiss mainly ranges from 200 to 300 Hz and is almost independent of L shell. The median values of ellipticity and electromagnetic planarity of exohiss waves are 0.91 and 0.54, respectively. Furthermore, the equatorward Poynting flux is comparable to the poleward Poynting flux at the equator and it becomes dominant at the absolute value of the magnetic latitude |λ|∼20°. Our observation results reveal the statistical features of exohiss waves for the first time and support the exohiss formation mechanism that exohiss originates from plasmaspheric hiss leakage. The results demonstrate exohiss as an important energy dissipation route for plasmaspheric hiss and significantly improve the understanding of plasmaspheric hiss evolution in the radiation belt region.

Effects of nonextensivity on the electron-acoustic solitary structures in a magnetized electron−positron−ion plasma

Obliquely propagating electron-acoustic solitary waves (EASWs) in a magnetized electron−positron−ion plasma (containing nonextensive hot electrons and positrons, inertial cold electrons, and immobile positive ions) are precisely investigated by deriving the Zakharov–Kuznetsov equation. It is found that the basic features (viz. polarity, amplitude, width, phase speed, etc.) of the EASWs are significantly modified by the effects of the external magnetic field, obliqueness of the system, nonextensivity of hot positrons and electrons, ratio of the hot electron temperature to the hot positron temperature, and ratio of the cold electron number density to the hot positron number density. The findings of our results can be employed in understanding the localized electrostatic structures and the characteristics of EASWs in various astrophysical plasmas.

Qualitative structures of electron-acoustic waves in an unmagnetized plasma with q-nonextensive hot electrons

The qualitative structures of electron-acoustic waves are investigated in an unmagnetized plasma containing cold electron fluid, q-nonextensive hot electrons and stationary ions. Applying the phase plane analysis, we present all phase portraits of the dynamical system and corresponding solitary- and periodic-wave solutions. Considering an external periodic perturbation, we study the chaotic structure of the perturbed dynamical system. The non-extensive parameter (q), the ratio between hot electron and cold electron number density at equilibrium (α) and speed of the traveling wave (v) play crucial roles for electron-acoustic solitary, periodic and chaotic structures. The results may have relevance in laboratory plasmas as well as space plasma environments.

Modulational instability of electron-acoustic waves in a plasma with Cairns–Tsallis distributed electrons

The problem of the modulational instability (MI) of electron-acoustic waves (EAWs) in a plasma with Cairns–Tsallis distributed electrons is addressed. Using the standard multiple scale method, we derive a nonlinear Schrödinger-like equation. Electron nonextensivity and nonthermality are found to significantly influence the region stability of the EAWs. In particular, it is found that the critical value kc, beyond which the instability sets in, is slightly lowered as the electrons evolve far away from their Maxwellian thermodynamic equilibrium. Electron nonthermality renders more effective and more important the influence and role of nonextensivity. Moreover, the effect of the unperturbed hot electron and cold electron number density imbalance μ on the onset of the MI is analyzed. Although both dark and bright excitations are obtained, the trend is in contrast to our earlier observations. Our results should be of relevance in wave propagation stability. Nonthermal nonextensive models may play an increasingly important role in predicting complex plasma behavior, and understanding the underlying physical processes.

Effects of cold electron number density variation on whistler-mode wave growth

Abstract. We examine how the growth of magnetospheric whistler-mode waves depends on the cold (background) electron number density N0. The analysis is carried out by varying the cold-plasma parameter a = (electron gyrofrequency)2/(electron plasma frequency)2 which is proportional to 1/N0. For given values of the thermal anisotropy AT and the ratio Nh/N0, where Nh is the hot (energetic) electron number density, we find that, as N0 decreases, the maximum values of the linear and nonlinear growth rates decrease and the threshold wave amplitude for nonlinear growth increases. Generally, as N0 decreases, the region of (Nh/N0, AT)-parameter space in which nonlinear wave growth can occur becomes more limited; that is, as N0 decreases, the parameter region permitting nonlinear wave growth shifts to the top right of (Nh/N0, AT) space characterized by larger Nh/N0 values and larger AT values. The results have implications for choosing input parameters for full-scale particle simulations and also in the analysis of whistler-mode chorus data.

Modulational instability of electron-acoustic waves in magnetized plasma in presence of excess superthermal electrons

Modulational instability of finite amplitude electron-acoustic waves along external magnetic field is investigated in plasma composed of inertial cold electrons, hot inertialess superthermal electrons and stationary ions. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schrodinger equation which governs the slow modulation of electron acoustic wave packets. Accounting for effects of hot electron to cold electron number density ratio (α), normalized electron-cyclotron frequency (ω c ) as well as the electron superthermal parameter (κ e ) new regimes for modulational instability of electron acoustic waves are obtained and analyzed. The presence of superthermal electrons modifies conditions for modulational instability to occur, as well as associated threshold and growth rate. Concentration of superthermal electrons (i.e., the deviation from a Maxwellian electron distribution) may control or even suppress modulational instability. In contrast to one-dimensional unmagnetized plasmas, instability growth rate is shown to suppress increasing values of k.

Linear and nonlinear modified electron-acoustic waves

It is shown that a modified electron-acoustic wave exists in a plasma with distinct hot and cold electron components. The frequency of this wave depends strongly on the cold electron number density. Solitons associated with the modified electron-acoustic waves are also discussed.