Cold Electron Density Research Articles

Arbitrary amplitude electron acoustic solitary excitations with Cairns–Tsallis distributed hot electrons and positrons in magnetized space plasmas

A rigorous theoretical study is performed to understand the characteristics of nonlinear electron acoustic (EA) solitary waves propagating in collisionless magnetized plasma system comprising cold inertial electrons, nonthermal–nonextensive hot electrons and positrons and stationary ions. The propagation and evolution of two potential modes (fast and slow) are studied in the linear regime. By employing magnetic hydrodynamic equations and with the aid of travelling wave approximation, the nonlinear wave dynamics is demonstrated by the first integral of motion in the form of a pseudo-energy balance equation. In exploring the EA soliton characteristics, numerical results reveal that only negative polarity EA solitons exist in a restricted range of the physical parametric space of the plasma system. It is revealed that the effects of nonthermal and nonextensive parameters, hot to cold electron density ratio, Mach number and magnetic strength considerably modify the basic properties of solitary waves. The present results may be important in space plasmas as well as laboratory plasmas with non-Maxwellian particle population.

A Mechanism for Large-Amplitude Parallel Electrostatic Waves Observed at the Magnetopause

Large-amplitude electrostatic waves propagating parallel to the background magnetic field have been observed at the Earth’s magnetopause by the Magnetospheric Multiscale (MMS) spacecraft. These waves are observed in the region where there is an intermixing of magnetosheath and magnetospheric plasmas. The plasma in the intermixing region is modeled as a five-component plasma consisting of three types of electrons, namely, two counterstreaming hot electron beams and cold electrons, and two types of ions, namely, cold background protons and a hot proton beam. Sagdeev pseudo-potential technique is used to study the parallel propagating nonlinear electrostatic solitary structures. The model predicts four types of modes, namely, slow ion-acoustic mode, fast ion-acoustic mode, slow electron-acoustic mode and fast electron-acoustic modes. Except the fast ion-acoustic mode, all other modes support solitons. Whereas slow ion-acoustic solitons have positive potentials, both slow and fast electron-acoustic solitons have negative potentials. For the case of 4% cold electron density, the slow ion-acoustic solitons have electric field ∼(40–120) mV m−1. The fast Fourier transforms (FFT) of slow ion-acoustic solitons produce broadband frequency spectra having peaks between ∼100 Hz to 1000 Hz. These theoretical predictions are in good agreement with the observations. The slow and fast electron-acoustic solitons could be relevant in explaining the low-intensity high (>1 kHz) frequency waves which are also observed at the same time.

Study of two-electron temperature plasma sheath using non-extensive electron distribution in presence of an external magnetic field

In this study, the physics of sheath formation in a collisional two-electron temperature plasma in the presence of an oblique external magnetic field has been investigated. At first, a comparative study among the fluid electron model, Boltzmann electron model, and the non-extensive electron model has been carried out and a suitable range of non-extensive parameter q has been predicted. In the latter part, a collisional two-electron temperature plasma is considered. Both the hot and cold electron densities are described using the non-extensive distribution, whereas cold ions are described by the fluid equations. The properties of the sheath are investigated in different collisional regimes by varying the non-extensive parameter (q) and the hot to cold electron densities and temperatures. The magnetic field inclination angle is varied in the limit 1° ≤ α ≤ 5°. It is observed that electron distribution significantly deviates from Boltzmann distribution for nearly parallel magnetic field. Moreover, collision enhanced flux deposition for highly magnetized case is a significant finding of the study. The results obtained in this study can enhance the understanding of plasma–matter interaction processes where multiple electron groups with near parallel magnetic field are found.

Effect of Two Different Electron Temperatures in Auroral Ionosphere

We have investigated the effect of two different electron temperatures in an auroral ionosphere in the presence of ions and obtained a modified electron-acoustic and modified lower-hybrid drift dissipative modes which will not be affected much due to the presence of cold electrons. However, in the drift dissipative case, the growth rate of the electron-acoustic wave depends on the number density of cold electrons.

H- and D- production efficiency in a multi-dipole ECR-plasma source as a function of gas pressure

The electron cyclotron resonance (ECR) negative ion source “Prometheus I” is operated either with high purity H2 (> 99.999%) or D2 (> 99.8%) to probe H- and D- ions, respectively, and examine the isotope effect within a wide range of gas pressure. These ions are predominantly formed in the bulk plasma by dissociative attachment (DA) of low-energy (cold) electrons to highly ro-vibrationally excited molecules. The latter result mainly from the radiative decay and excitation (EV) process sustained by high-energy (hot) electrons heated in the ECR zones. Langmuir probe and laser photo-detachment measurements are realized within the pressure range 0.27 to 2.67 Pa under constant microwave power (0.9 kW). It is revealed that: (i) the plasma potential, cold electron temperature, and cold electron density tend to be higher in deuterium; (ii) no pronounced difference in the hot electron density and temperature is found between the two plasmas; and (iii) overall a similar H- and D- negative ion yield (up to 6×109 cm-3; under the present conditions) is achieved. However, for equal plasma densities an isotope effect is exhibited showing higher H- density over the entire pressure range. Finally, the nH- / n ratio is constantly higher than the nD- / ne one and they both peak around 1.33 Pa.

Monitoring Space Weather: Using Automated, Accurate Neural Network Based Whistler Segmentation for Whistler Inversion

AbstractIt is challenging, yet important, to measure the—ever‐changing—cold electron density in the plasmasphere. The cold electron density inside and outside of the plasmapause is a key parameter for radiation belt dynamics. One indirect measurement is through finding the velocity dispersion relation exhibited by lightning induced whistlers. The main difficulty of the method comes from low signal‐to‐noise ratios for most of the ground‐based whistler components. To provide accurate electron density and ‐shell measurements, whistler components need to be detectable in the noisy background, and their characteristics need to be reliably determined. For this reason, precise segmentation is needed on a spectrogram image. Here, we present a fully automated way to perform such an image segmentation by leveraging the power of convolutional neural networks, a state‐of‐the‐art method for computer vision tasks. Testing the proposed method against a manually, and semi‐manually segmented whistler data set achieved 10% relative electron density prediction error for 80% of the segmented whistler traces, while for the shell, the relative error is 5% for 90% of the cases. By segmenting more than 1 million additional real whistler traces from Rothera station Antarctica, logged over 9 years, seasonal changes in the average electron density were found. The variations match previously published findings, and confirm the capabilities of the image segmentation technique.

Quantum Electron Acoustic Solitons and Double Layers with κ-deformed Kaniadakis Distributed Electrons

The present investigation is dedicated to the study of propagation characteristics of electron acoustic (EA) waves and double layers in the quantum plasma system containing inertialess hot electrons and inertial cold electrons with stationary ions forming the charge neutralizing background. It is assumed that hot electrons follow κ-deformed Kaniadakis distribution as governed by the parameter κ. Using the appropriate stretched coordinates and reductive perturbation method (RPM) the Korteweg-de Vries (KdV) and modified KdV (mKdV) equations have been derived. For the sake of analysis, a limit of range of deformation parameter (κ) has been set as -0.4≤κ≤0.4. For the defined range, it has been observed that plasma system supports rarefactive solitary structures. The amplitude and width of KdV soliton have been significantly affected by the quantum effects and remains unaffected by the deformation parameter (κ). The analysis was further extended to the derivation of mKdV equation to investigate the existence of small amplitude double layers (DLs). Only negative potential DLs are found to exist whose dynamics significantly depends on deformation parameter (κ), quantum effects (H) and hot to cold electron density ratio (α). The outcome of the present discourse may be helpful to understand the use of generalized entropies in the environment of plasma physics.

Beam-driven ECH waves: A parametric study

Electron cyclotron harmonic (ECH) waves play a significant role in driving the diffuse aurora, which constitutes more than 75% of the particle energy input into the ionosphere. ECH waves in magnetospheric plasmas have long been thought to be excited predominantly by the loss cone anisotropy (velocity–space gradients) that arises naturally in a planetary dipole field. Recent THEMIS observations, however, indicate that an electron beam can also excite such waves in Earth's magnetotail. The ambient and beam plasma conditions under which electron beam excitation can take place are unknown. Knowledge of such conditions would allow us to further explore the relative contribution of this excitation mechanism to ECH wave scattering of magnetospheric electrons at Earth and the outer planets. Using the hot plasma dispersion relation, we address the nature of beam-driven ECH waves and conduct a comprehensive parametric survey of this instability. We find that growth is provided by beam electron cyclotron resonances of both first and higher orders. We also find that these waves are unstable under a wide range of plasma conditions. The growth rate increases with beam density, beam velocity, and hot electron temperature; it decreases with increasing beam temperature and beam temperature anisotropy (T⊥/T∥), hot electron density, and cold electron density and temperature. Such conditions abound in Earth's magnetotail, where magnetospheric electrons heated by earthward convection and magnetic reconnection coexist with colder ionospheric electrons.

Non‐linear coherent structures in multi‐species dusty plasma

AbstractIn a fluid description, theoretical investigation has been carried out to explore how the presence of two‐temperature electron fluids (hot and cold) influences the characters of dust acoustic solitary waves, double layers, bipolar structures, etc. in a multi‐component dusty plasma, composed of isothermal electrons and ions, along with the negatively charged, cold dusts. A reductive perturbation method is used to derive the well‐known Korteweg‐de Vries (KdV) equation, which describes the basic nature of the dust acoustic solitary waves. Two values of critical ion density exist, which distinguish the regions of compressive and rarefactive solitary waves in parametric space. The critical points directly depend on the densities and temperatures of the electron fluids. With increasing temperature of hot electron fluid, one of the two critical ion densities decreases, and the other one increases. Ultimately, they merge with each other when the temperature of hot electrons reaches a particular value. The amplitude of the dust acoustic soliton gets modified due to the presence of two‐temperature electron fluids. The study is extended further by deriving modified KdV and Gardner equations at the vicinity of critical points. The Gardner equation reveals the existence of double layer and bipolar structures. In these processes, the effects higher‐order nonlinearities are incorporated methodically, by implementing appropriate stretching of the coordinates. Sagdeev's pseudopotential analysis shows that large amplitude rarefactive solitary waves only exist when the corresponding Mach number (M) lies within 1 < M < Mc. The upper bound, Mc increases with the hot electron temperature and cold electron density. The results presented in this investigation are believed to be applicable in the laboratory and astrophysical plasmas.

Mode Coupling From Kinetic Alfvén Waves to Electron Acoustic Waves in the Topside Ionosphere

AbstractThe propagation and energy transfer of kinetic Alfvén waves (KAWs) in the topside ionosphere are investigated based on a drift kinetic model. We examine the dependence of the generation of electron acoustic waves (EAWs) on the perpendicular wavelength and on the hot electron temperature. With decreasing perpendicular wavelength and increasing hot electron temperature, the coupling of KAWs to EAWs becomes increasingly important. The Landau damping of the EAWs is strong except in the transition region, where the nonlinear dissipation can be important. With increasing wave amplitude, the generated electron acoustic mode waves become unsustainable when the depletion of cold electron density is comparable to the initial background cold electron density. These findings indicate that electron acoustic mode waves play an important role at kinetic scales in the topside ionosphere.

Parametric study of cylindrical and spherical dust ion acoustic shock waves with two temperature electrons in dusty plasma relevant to Saturn's E ring

AbstractWe have performed numerical analysis of the one‐dimensional dynamics of the cylindrical/spherical dust ion acoustic shock waves in unmagnetized dusty plasma consisting of positive ions, immobile dust particles, and nonextensive distributed cold and hot electrons. A multiple‐scale expansion method is used to derive Burgers Equation (BE) and modified Burgers equation (MBE) by including higher order nonlinearity. The basic characteristics of the shock waves have been analysed numerically and graphically for different physical parameters relevant to Saturn' E ring through 2D figures. The parametric dependence of dust ion acoustic shock waves on some plasma parameters nonextensive index, density, and temperature of cold and hot electrons, concentration of dust particles, thermal effects and kinematic viscosity of ions is explored. Furthermore, it is found that the nonplanar geometry effects have an important impact on the establishment of shock waves. The amplitude of the wave decreases faster as one departs away from the axis of the cylinder or centre of the sphere. Such decaying behaviour continues as time progresses. It is also found that an increasing dust concentration decreases the amplitude of the dust ion acoustic shock waves.

Cylindrical and spherical ion acoustic shock waves with two temperature superthermal electrons in dusty plasma

In the present study, the cylindrical/spherical ion acoustic shock waves have been investigated in unmagnetized dusty plasma consisting of positive ions, immobile dust particles and kappa distributed cold and hot electrons. A multiple scale expansion method is employed to derive Burgers equation (BE) and modified Burgers equation (MBE) by including higher order nonlinearity. The basic characeristics of the shock waves have been analyzed numerically and graphically for different physical parameters relevant to space and laboratory dusty plasma environments through 2D figures. We show that the amplitude of the wave decreases faster as one departs away from the axis of the cylinder or centre of the sphere. Such decaying behaviour continues as time progresses. Furthermore, the parametric dependence of wave properties (amplitude, width) on kappa index, density and temperature of cold and hot electrons, concentration of dust particles, thermal effects and kinematic viscosity of ions has been studied in detail and findings obtained here will be beneficial to further astrophysical investigations.

The Modulation of Plasma and Waves by Background Electron Density Irregularities in the Inner Magnetosphere

AbstractThe background cold electron density plays an important role in plasma and wave dynamics. Here, we investigate an event with clear modulation of the particle fluxes and wave intensities by background electron density irregularities based on Van Allen Probes observations. The energies at the peak fluxes of protons and Helium ions of 100 eV to several keV are well correlated with the total electron density variation. Intense electromagnetic ion cyclotron (EMIC) and magnetosonic (MS) waves are simultaneously observed in the high‐density regions and disappear in low‐density regions. Based on the linear theory of wave growth, the EMIC waves are generated by the ~10 keV protons, while most MS waves are generated by the positive gradient of proton phase space density at several hundred eV in the high‐density regions. Our results indicate the importance of background plasma density structures in generation of plasma waves by unstable ion distributions.

Nonplanar ion acoustic waves in dusty plasma with two temperature electrons: Application to Saturn's E ring

In the present paper, we have studied the cylindrical/spherical ion acoustic waves in dusty plasma consisting of positive ions, immobile dust particles, and q nonextensive distributed cold and hot electrons. A multiple scale expansion method is employed to derive a modified Korteweg–de Vries (mKdV) equation. Exact analytical solution for the mKdV equation in nonplanar geometry is obtained using the weighted residual method. This solution is, then, plotted for different physical parameters relevant to Saturn's E ring through 2D figures. We show that the amplitude of the wave decreases faster as one departs away from the axis of the cylinder or the center of the sphere. Such a decaying behavior continues as time progresses. This is expected from the obtained solution where the cylindrical (spherical) amplitude component (τ∞/τ)m decreases as the time progresses. We have also studied the role of the nonadiabatic dust charging fluctuating dissipation process and analyzed the resulting damped mKdV equation. Furthermore, the parametric dependence of wave properties (amplitude and width) on the q nonextensive parameter, density, and temperature of cold and hot electrons, concentration of dust particles, and thermal effects of ions has been studied in detail, and findings obtained here will be beneficial to further astrophysical investigations.

Nonlinear ion acoustic waves in dissipative and dispersive magneto‐rotating relativistic plasmas with two temperature superthermal electrons

AbstractA study has been presented for the nonlinear features of ion‐acoustic (IA) shock waves in a magnetorotating plasma consisting of warm viscous streaming ions along with kappa‐distributed electrons having two different temperatures. In this regard, we have employed the reductive perturbation technique to derive the Zakharov‐Kuznetsov‐Burgers (ZKB) equation that governs the dynamics of IA shock waves. The solution obtained by the hyperbolic tangent method has been shown to depend on various plasma parameters such as spectral index (κc), density fraction (f), effective rotation frequency (Ωc), ion kinematic viscosity (ηo), and temperature ratio (σ). In the limiting case when dissipative coefficient D → 0, we have also examined the solitary potential distributions, which are the solutions of Zakharov Kuznetsov (ZK) equation. It is found that both rarefactive and compressive structures exist for the system under consideration. The transition in the nature of such profiles is due to the enhancement in the density of cold electrons. The importance of present theoretical investigations has been carried out with regard to Saturn's magnetosphere, where two temperature superthermal electron populations have been observed by various satellite missions.

Effect of particle trapping in a three-component plasma sheath model containing Tsallis distributed electrons

In this paper, the effect of particle trapping in a three-component plasma sheath model has been investigated analytically. The behavior of plasma sheath is studied with cold fluid ions, trapped/vortex-like hot electrons and cold q-nonextensive electrons. The trapped hot electrons follow Schamel’s vortex-like distribution. A modified Bohm sheath criterion and a sheath width equation have been analytically derived. It is seen that the thickness of the sheath explicitly depends on q-nonextensivity parameter, Bohm velocity, cold electron fraction, temperature and densities of cold and hot electrons; while the Bohm velocity depends on nonextensive parameter, fraction of cold electrons, temperature and densities of cold and hot electrons. It is observed that as the electron nonextensivity as well as fraction of cold electron increases, the Bohm velocity decreases and also the sheath width decreases. As the ratio between hot electrons temperature to cold electrons temperature increases, the Bohm velocity increases and the sheath thickness also increases. The increasing values of the ratio of cold electrons to hot electrons concentration results in the decrease of sheath width.

Formation of solitary structures and envelope solitons in electron acoustic wave in inner magnetosphere plasma with suprathermal ions

AbstractThe propagation of electron acoustic solitary waves is investigated in magnetized two‐temperature electron plasma with supra‐thermal ion. By using the reductive perturbation technique, the Korteweg de‐Vries (KdV) equation is derived. Later solving this equation, a solitary wave solution has been derived. These are mainly in astrophysical plasmas where changes of local charge density, temperature, and energy of particles produce considerable effects on the plasma system. The effects of supra‐thermality, density, and Mach number on solitary structures are studied in detail. The results show that the supra‐thermal index (κ) and ion to electron temperature ratio (σ) alters the regime where solitary waves may exist. While studying the solitary profile for different parametric variation some interesting conclusion can be drawn; it is shown that the solitary profile becomes flatter. This can be due to the thermal energy associated with the hot electrons. However, with the increase in ion density with respect to the cold electrons' density, the solitary waves become steeper and sharper. This is due to the comparatively heavier mass of ions. The density of cold electron also increases the solitary structures in a similar manner. The higher the density of cold electrons, sharper will be the profile. The above findings will be helpful in understanding many astrophysical phenomena and data obtained by space missions. For a further study, we keep the investigation of the formation of other kinds of stationary structures like shocks, double layers, etc.

Eastward Propagating Second Harmonic Poloidal Waves Triggered by Temporary Outward Gradient of Proton Phase Space Density: Van Allen Probe A Observation

AbstractTwo wave packets of second harmonic poloidal Pc 4 waves with a wave frequency of ~7 mHz were detected by Van Allen Probe A at a radial distance of ~5.8 RE and magnetic local time of 13 hr near the magnetic equator, where plasmaspheric refilling was in progress. Proton butterfly distributions with energy dispersions were also measured at the same time; the proton fluxes at 10–30 keV oscillated with the same frequency as the Pc 4 waves. Using the ion sounding technique, we find that the Pc 4 waves propagated eastward with an azimuthal wave number (m number) of ~220 and ~260 for each wave packet, respectively. Such eastward propagating high‐m (m > 100) waves were seldom reported in previous studies. The condition of drift‐bounce resonance is well satisfied for the estimated m numbers in both events. Proton phase space density was also examined to understand the wave excitation mechanism. We obtained temporal variations of the energy and radial gradient of the proton phase space density and find that temporal intensification of the radial gradient can generate the two wave packets. The cold electron density around the spacecraft apogee was >100 cm−3 in the present events, and hence the eigenfrequency of the Pc 4 waves became lower. This causes the increase of the m number which satisfies the resonance condition of drift‐bounce resonance for 10–30 keV protons and meets the condition for destabilization due to gyrokinetic effect.

Generation of series of electron acoustic solitary wave pulses in plasma

One-dimensional fluid simulation is used to investigate the generation of electron-acoustic solitary waves (EASWs) in three-species plasma. We consider an unmagnetized collisionless plasma consisting of cold electrons, hot electrons, and ions. The Gaussian perturbations in the equilibrium electron and ion densities are used to excite the waves in the plasma. This simulation demonstrates the generation of a series of EASW pulses in this three-species plasma through the process of wave breaking. We investigate the behavior of the ponderomotive potential, frequency, and force associated with electrons and ions during the process of the wave breaking. We observed that the ponderomotive potential of the hot electron, which is the driving species for the electron acoustic waves, peaks at the time of wave breaking. The variation of the maximum ponderomotive force acting spatially on the leading and trailing edges of the hump in the cold and hot electron and ion fluid densities shows the maximum imbalance in the magnitude of the ponderomotive force acting on both sides of the hot electron density hump at the time of wave breaking. This reveals that the imbalanced ponderomotive force acting on the hot electron fluid is responsible for the breaking of the electron acoustic wave in plasma. Furthermore, it is observed that the wave breaking process occurs at an earlier time if the hot electron temperature is increased.

Kinetic Theory of Ion Acoustic Waves Observed at Comet 67P/Churyumov–Gerasimenko

Abstract This work presents the resonance interaction of ion acoustic waves with the cometary plasma as observed at comet 67P/Churyumov–Gerasimenko. The plasma is comprised of cold, warm, and suprathermal electron populations and water ions such that the quasineutrality is satisfied. The cold electron population is found to play a dominant role in the damping of the waves, and its maximum Landau damping rate is observed when it is 2% of the total electron density in the system. It is determined that lowering the cold electron density supports the current-driven ion acoustic instability at a relatively lower drift speed of the warm and suprathermal electron species. In the absence of cold electrons, the wave phase speed does not change by populating the high-energy suprathermal electron species, therefore, the Landau damping rate of both warm and suprathermal electrons increases by increasing their respective densities. The growth rate of the current-driven ion acoustic instability decreases by elevating the concentration of suprathermal electrons in the case of drifting warm and stationary suprathermal electrons. In the case of stationary warm and drifting suprathermal electrons, the elevated density of suprathermal electron instead favors the instability.