non-Maxwellian Electrons Research Articles

Revisiting lunar dust charging and dynamics

Under the dynamic influence of near-surface plasma, intricate dynamics of lunar dust have been observed during the Surveyors and Apollo missions in the form of Lunar horizontal glow. These dynamics are primarily driven by electrostatic forces generated by the continual bombardment of solar wind and highly energetic UV photons on the lunar surface and dust particles. This paper revisits the phenomenon of dust charging within the lunar photoelectron sheath and subsequent dynamics. The investigation has been carried out using a comprehensive model of the lunar photoelectron sheath characterized by observed solar spectra, latitude-dependent Fermionic photoelectrons, non-Maxwellian solar wind electrons, and cold ions. A test dust particle is introduced into the sheath, and equilibrium charge and static levitation conditions are derived. The result of dynamical evolution suggests the existence of a narrow parametric regime corresponding to the periodic hopping trajectory of the dust particle over the lunar surface. In other cases, the dust particles are found to re-impact the surface after a single ballistic hop. We further identify that the discrete charging of the dust could be crucial in determining the dust dynamics, particularly in the tenuous plasmas. The analysis of the discrete dust charging model reveals significant discrepancies with the continuous dust charging model and suggests a lower likelihood of static dust levitation in the lunar environment. The present study is important for unraveling the fundamental processes governing surface evolution on the Moon and other airless bodies throughout the Solar System.

Self-generated magnetic field in laser plasma with super-Gaussian distributed electrons

Considering the effects of non-Maxwellian distributed electrons and the generation of magnetic field on the inertial confinement fusion driven by laser, the quasi-static magnetic field generated by nonlinear magnetization current in laser plasma with super-Gaussian distributed electrons is studied. Based on the kinetic theory, an analytical expression for the spontaneous magnetic field in Fourier space, valid for arbitrary frequencies, has been obtained. According to the existing experimental data, the effects of the frequency, plasma temperature, and super-Gaussian index on the spontaneous magnetic field are analyzed through numerical calculations. It is shown that the strength of the spontaneous magnetic field first decreases and then increases with the increase in the super-Gaussian index when the laser intensity is ∼1012W/cm2. It is about the order of 100 G, which is much smaller than the experimental observation. When the laser intensity is ∼1016W/cm2, the strength of the spontaneous magnetic field increases monotonically with the super-Gaussian index in the low-frequency region, and behaves similarly to the one of the laser intensity ∼1012W/cm2 in the high-frequency region. It will be as large as megagauss, which is consistent with the experimental observation results. Moreover, the strength of the spontaneous magnetic field increases with the increase in frequency and the decrease in the electron temperature.

Versatile multi-energy hard x-ray camera to study confined and unconfined fast electron dynamics and anisotropies (Invited).

A powerful and flexible hard x-ray (HXR) camera has been recently installed and tested on the WEST tokamak (CEA, France) in collaboration with the Princeton Plasma Physics Laboratory. The diagnostic is a pinhole camera fielded with a 2D pixel detector equipped with a 1mm thick CdTe sensor. The novelty of this diagnostic technique is the detector's capability of adjusting the threshold energy at the pixel level. This innovation provides great flexibility in the energy configuration, allowing simultaneous space, energy, and time resolved x-ray measurements. The novel camera has been used to measure the core radiation from non-Maxwellian (fast) electrons accelerated by Lower Hybrid (LH) waves and also the beam-target emission of tungsten in the divertor region produced by fast electron losses interacting with the target. In addition, anisotropic hard x-ray emission has been detected for the first time at the WEST core and edge plasma, with opposite toroidal intensity trends. Experimental vertical and toroidal HXR profiles have been successfully reproduced with the LH code LUKE.

Ion-acoustic solitons in multicomponent plasma with two temperature non-Maxwellian electrons

The study of ion-acoustic solitons (IASs) in an unmagnetised collisionless plasma system having inertial fluid ions and two temperature hot as well as cold electrons obeying Cairns–Tsallis (CT) distribution is presented. Using reductive perturbation method, the KdV equation is derived. Further, introducing higher-order effects of nonlinearity and dispersion, a nonlinear KdV-type inhomogeneous equation is derived that supports the formation of dressed solitons. The combined effects of higher-order corrections and various plasma parameters are analysed on the characteristics of the different kinds of ion-acoustic solitons with implications to Saturn's magnetosphere.

Nonplanar ion acoustic waves in e-p-i plasmas with non-Maxwellian distributed electrons and positrons

The process of propagation of cylindrical and spherical ion acoustic solitary waves in an electron, positron, and ion plasma system is studied. The electrons are considered to have the generalized (r, q) distribution, while the positrons are supposed to have the kappa distribution, also known as the Lorentzian distribution. The classic nonlinear equation, Korteweg de-Vries (KdV), has been numerically solved by employing appropriate mathematical transformations. The role of various plasma parameters and nonplanar geometry on the widths and amplitudes of nonlinear ion acoustic structures has been numerically investigated. The current study could be helpful to understand the significance of cylindrical and spherical solitary waves in laboratory, astrophysical as well as in space plasmas.

Effects of dust size distribution and non-Maxwellian electrons on shock waves in a dusty plasma

We present a study of dust acoustic shock waves in a non-Maxwellian plasma with dust charge fluctuations, which are seen to cause a dissipation term in fluid model, and consequently shocks are generated. In particular, we focus on dust acoustic waves as affected by various dust size distributions. Two distinct dust size distributions—the polynomial and the power law distributions—have been used. For analytical investigation of nonlinear wave propagation in complex plasmas, a reductive perturbation approach is used to obtain the Burgers equation. A dusty plasma system with non-Maxwellian Kappa distribution is considered and it is shown that the amplitude of a shock wave, for the dust size distribution is larger than that for the mono-sized counterpart, while the shock width manifests an opposite trend. Furthermore, the shock wave speed is also affected by the dust size distributions as well as by the nature of velocity distribution function. To benchmark our findings, we apply the proper limit on the spectral index, i.e., κ→∞, and retrieve the Maxwellian results. The current findings are crucial for comprehending respective shock distributions for a plasma system exhibiting non-thermal characteristics and having dust size distributions.

Charge fluctuations on the dust grains in the presence of energetic electrons

Abstract Dust charging is an arbitrary process occurring at random times which results in fluctuations of dust charge around its equilibrium value. To have a better insight into the mechanism of charge fluctuations, a numerical simulation of the statistical nature of the dust charging process is investigated. Here, a multicomponent non-Maxwellian hydrogen plasma comprising two electron groups, positive ions, and dust grains is modelled. An increase in the overall negative dust charge number is reported in the presence of non-Maxwellian electrons. Additionally, the study emphasizes the role of electron distribution and hot electron temperature and density on the charge fluctuations of the dust grains.

Kinetic Alfvén solitary waves in a low-β plasma with regularized kappa-distributed electrons

This study examines the characteristics of small-amplitude kinetic Alfvén waves (KAWs) in a typical magnetoplasma, where both ions and electrons are considered to have a regularized kappa distribution (RKD). The restrictions imposed on the standard Kappa distribution function will be removed by considering the RKD function. The RKD can also be used for kappa areas for spectral index κ < 3/2. We then use the Korteweg–de Vries equation to investigate the KAWs in this model, which we obtained from the reductive perturbation method. It is observed that the equation’s nonlinear and dispersive coefficients are functions of the Kummar functions and the cut-off parameter. It is found that the nonlinear and dispersive coefficients of this equation depend on the Kummar functions and the cut-off parameter. Due to the negativity of the coefficients of the wave equation, only compressive KAWs can exist and propagate in this model. The numerical results demonstrate a positive correlation between the soliton’s profile (amplitude and width) with an increase in the cut-off parameter. Conversely, the superthermality has a negative influence on the soliton profile. The influence of the soliton’s propagation angle on the magnetic field’s direction is investigated. It is found that the solitary wave will not propagate in the ambient when the propagation angle θ becomes 0 or 90. Overall, the results obtained from this research can be used in space and laboratory plasmas with low β that have non-Maxwellian electrons.

Multi-ion magnetized sheath properties with non-extensive electron distribution

Magnetized plasma sheath plays an important role in semiconductor processing, material surface modification, film deposition, etc. In plasma experiments and discharge applications, multi-ion plasma consisting of more than two kinds of ions often exists. For a long range interacting plasma system, non-Maxwellian electrons can be described by the non-extensive distribution of Tsallis. In this work, a fluid model with one-dimensional spatial coordinates and three-dimensional velocity coordinates is established for the multi-ion plasma sheath. It is assumed that the electron velocity in the sheath follows a non-extensive distribution, and the background helium ions and different kinds of impurity ions are magnetized in a magnetic field with a certain tilt angle. The effects of non-extensive parameters, impurity ions and oblique magnetic field on the number density, velocity, wall potential and kinetic energy of ions in the multi-ion magnetic sheath are investigated by numerical simulation. The results show that in the helium-hydrogen or helium-argon mixed plasma sheath, the ionic velocity along the vertical wall direction decreases with the increase of the non-extensive parameters, the number density of ions and electrons in the sheath, the sheath thickness , and the kinetic energy of ions at the wall decrease. When the concentration of impurity ions increases, the kinetic energy of ions on the wall is independent of the type of ions. With the increase of magnetic field intensity, the number density of helium ions and the velocity along the vertical wall fluctuate along the sheath edge, and the fluctuation amplitude increases with the decrease of non-extensive parameters, while the heavy ions have no obvious fluctuation. In addition, the effects of the types and concentrations of impurity ions on the related properties of the sheath are also analyzed. With the increase of the magnetic field intensity, the number density and the velocity along the vertical wall direction fluctuate at the sheath edge, and the fluctuation amplitude increases with the decrease of the non-extensive parameter, whereas there are no significant fluctuations for heavy ions. In addition, when impurity ions are heavy ions, the absolute value of wall potential increases with the increase of impurity ion concentration and the decrease of non-extensibility parameters, and the kinetic energy of background ions increases at the wall surface. When the impurity ion is a light ion, the absolute value of the wall potential decreases with the increase of the impurity ion concentration and the decrease of the non-extensibility parameter, and the kinetic energy of the background ion at the wall decreases.

On the arbitrary amplitude ion-acoustic structures in an anisotropic non-Maxwellian electron–positron–ion magnetoplasma

This paper comprehensively investigates the oblique propagation of ion-acoustic solitary waves (IASWs) with arbitrary amplitude in a magnetoplasma consisting of inertialess non-Maxwellian (nonthermal) electrons, inertialess Maxwellian positrons, and inertial adiabatically heated ions. It is postulated that the positive ions demonstrate adiabatic behavior that is distinguished by anisotropic thermal pressure. The study utilizes Sagdeev's pseudopotential theory to analyze the fluid equations of the plasma model and reduce them to the energy equation. Different plasma configuration factors, such as nonthermal parameters, positron concentration, and parallel and perpendicular ion pressure, are being studied to see how they affect the properties of solitary waves with large amplitudes. The findings demonstrate the simultaneous coexistence of compressive and rarefactive IASWs, significantly influenced by positrons and nonthermal electron parameters. The study provides valuable insights into wave phenomena in magnetized plasmas and presents possible applications in both Space and laboratory plasma environments.

Plasma Sheath around Chandrayaan-3 Landing Site: A Case Study

India’s lander-rover mission Chandrayaan-3 is scheduled to be launched in mid-2023. We have simulated a realistic scenario and investigated the electric potential development over the Chandrayaan-3 landing site under the influence of observed solar ultraviolet/extreme-ultraviolet radiation and real plasma parameters measured by THEMIS as a case study. The electric potential structures have been derived by solving Poisson’s equation, which is coupled with latitude-dependent fermionic photoelectrons, non-Maxwellian plasma electrons, and cold ions. A dynamic variation of the potential structure around the sunlit landing site has been observed through the analysis. This study predicts a photoelectron density range from 10 to 40 cm−3 and mean energy range from 2.6 to 3 eV near the surface of the Chandrayaan-3 landing site, which may be tested by the in situ measurement.

Dust-ion-acoustic shock waves in the presence of (r, q) distributed electrons

A three-component dusty plasma system, with non-Maxwellian electrons, is investigated. The ions are considered to be mobile, the (spherical) dust is assumed to be stationary with charge- fluctuations, and the electrons follow the generalized velocity distribution function (VDF). The respective Burger’s equation, which manifests a shock structure, is derived by employing a reductive perturbation technique (RPT). It is deduced that dust charge fluctuations induce shock potential in a collisionless plasma system. The resultant perturbed potential is evaluated as affected by different plasma parameters, e.g. the ratios of electron to ion temperature (σ i ) and equilibrium densities (μ), and the non-thermal indices r and q. The shock amplitude is seen to decrease when the value of σ i is increased, and vice versa, whereas an opposite trend is observed for μ. It is found that for r = 0 and increasing values of spectral index q, amplitude of the potential distribution enhances while its width decreases. It is further noted that non-Maxwellian VDF significantly modifies the potential distribution. For the limiting case, namely, r = 0 and q → ∞ , the corresponding Maxwellian results are retrieved which benchmarks our findings. Present work will be useful in understanding the nonlinear propagation of dust-ion-acoustic shock waves in system where non-thermal population—as caused by various physical processes—of electrons are observed.

On the oblique electrostatic waves in a dusty plasma with non-Maxwellian electrons for Saturn’s magnetosphere

The characteristics of (non)linear dust-ion acoustic waves (DIAWs) in a collisionless, magnetized dusty plasma are investigated. The current model is composed of ( r, q)-distributed electrons along with warm ions and stationary dust grains with negative charge. Both linear and nonlinear waves are considered to progress in x- z plane. The properties of linear waves are studied by deriving the dispersion relation for the plasma parameters of Saturn’s magnetosphere. The fluid equations of the current model are reduced to the universal Korteweg-de Vries (KdV) equation in order to study the characteristics of oblique propagation of DIA solitary waves (DIASWs). The critical point at which the nature/polarity of solitons changes is determined precisely. The influence of various plasma parameters, namely, obliqueness, magnetic field, densities, temperatures, and double spectral indices of the ( r, q)-distributed electrons on DIASWs is investigated for Saturn’s magnetosphere. The DIASWs of ( r, q)-distributed electrons are also compared with Maxwellian electrons. This work would be helpful to study other astrophysical and laboratory plasma systems where dusty plasmas and ( r, q) distribution are predicted.

Tripolar vortices in inhomogeneous magnetoplasmas in the presence of non-Maxwellian electron distributions

Nonlinear equations governing the characteristics of tripolar vortices (TPVs) are investigated in an inhomogeneous magnetoplasma having inertialess non-Maxwellian electrons that obey the Cairns, kappa, and (r, q)-distributions. Analytical and numerical solutions of the nonlinear equations are presented for various possible cases. In this regard, the dispersion relation for the drift ion-acoustic waves (IAWs) is derived, and the condition describing the shear flow instability is discussed. It is realized that enhancing the impact of non-Maxwellian electrons in the aforementioned three distributions modifies the size and formation of TPVs. It is found that the increase in the electron concentration in the regions of low-phase space density leads to enhancement in the size of TPVs and the perturbation potential as compared to the effect of increasing concentration of electrons in the regions of high phase space density. The riveting interplay of low and high-energy electrons with spiky distribution and the resulting novel effects on the propagation of vortex structures are also discussed in detail. The present study is useful to understand the (non)linear propagation characteristics of the drift IAWs in space plasmas with special reference to the F-region of the ionosphere and also in laboratory experiments where the nonthermal distribution functions are usually found.

On the propagation and interaction of ion-acoustic solitary, periodic, shock, and breather waves in a non-Maxwellian electron–positron–ion magnetoplasma

This investigation analyzes the propagation of nonlinear ion-acoustic waves (IAWs) in an unmagnetized, collisionless plasma composed of inertial positive ions and inertialess Maxwellian positrons as well as the inertialess non-Maxwellian electrons that obey (r, q)-distribution. To observe the impact of particle trapping on the nonlinear IAWs in an electron–positron–ion plasma, the Korteweg–De Vries (KdV) and modified KdV (mKdV) equations are derived using a reductive perturbation method. In the distribution function, the spectral parameters (r, q) put up their contribution to the flatness and high-energy tails, respectively. An important aspect of this investigation is the determination of well-known quasi-periodic solutions, multi-soliton solutions, breathers, and shocks under the variation of different physical parameters, especially spectral indices (r, q). Finally, the interaction of solitons is also presented for discussion of the complete profile. In addition, a detailed comparison, especially in a periodic wave, is made between the generalized (r, q)-distribution and the limiting cases of Kappa and Maxwellian distributions. The results presented in this study contribute to a better understanding of the characteristics of both high- and low-energy parts of the electron distribution function as well as the formation of periodic, soliton, multi-soliton, breathers, and shocks in space and astrophysical plasmas.

Hirota bilinear method and multi-soliton interaction of electrostatic waves driven by cubic nonlinearity in pair-ion–electron plasmas

Multi-soliton interaction of nonlinear ion sound waves in a pair-ion–electron (PIE) plasma having non-Maxwellian electrons including Kappa, Cairns, and generalized two spectral index distribution functions is studied. To this end, a modified Korteweg–de Vries (mKdV) equation is obtained to investigate the ion-acoustic waves in a PIE plasma at a critical plasma composition. The effects of temperature and density ratios and the non-Maxwellian electron velocity distributions on the overtaking interaction of solitons are explored in detail. The results reveal that both hump (positive peak) and dip (negative peak) solitons can propagate for the physical model under consideration. Two and three-soliton interactions are presented, and the novel features of interacting compressive and rarefactive solitons are highlighted. The present investigation may be useful in laboratory plasmas where PIE plasmas have been reported.

Plasma sheath around sunlit moon: monotonic and non-monotonic structures

ABSTRACTAn analytical investigation of the sheath formation over sunlit moon under the influence of observed solar ultraviolet/extreme ultraviolet radiation and solar wind plasma has been presented. Poisson’s equation is coupled with the latitude-dependent Fermionic photoelectrons, non-Maxwellian solar wind electrons and cold ions to derive the electric potential, electric field, and population density profiles within the photoelectron sheath. We notice that the high-energy photons of the solar spectra in addition to Lyman- α, significantly contribute in determining the surface charge and subsequent sheath structure. A traditional Debye (Type C) sheath forms around the terminator due to dominant plasma electron accretion and marginal photoemission. While moving towards the equator, the photoelectron contribution increases, yielding monotonic (Type B) and non-monotonic (Type A) sheath solutions over sunlit locations. The calculations show that the non-monotonic potential structures are more stable near the terminator region, while both types of potential structures are probable near the equator region for the nominal solar wind plasma. A vertical sheath extension of ∼60 m and ∼12 m is predicted for typical solar wind plasma at the equator corresponding to Type A and Type B sheath, respectively. Under exotic plasma conditions (e.g. Earth’s magnetospheric tail lobe, plasma sheet), non-monotonic solutions become stable for the photoemission-dominated region, and the entire sunlit lunar surface may acquire negative potential.

Comparison of Langmuir probe and optical emission spectroscopy on a volume-cusp filament ion source using helium.

D-Pace has a Penning ion source that runs with helium for studies of α-particle production. We want to study its plasma properties as a function of varying operational parameters, which results in varied output ion beam characteristics. In order to diagnose the ion source plasma, a collisional-radiative code for helium to be used with optical emission spectroscopy measurements is developed. This has the advantage of being non-invasive, which allows for measurements using the emitted light from the plasma. This collisional-radiative code is shown to compare well with the Yacora on the Web model developed at IPP-Garching, and improves upon it with the addition of radiation trapping. Furthermore, the sensitivity of this model to the inclusion of additional excited state populations and non-Maxwellian electron energy distribution functions is investigated. It is shown that non-Maxwellian distributions can significantly affect spectroscopy measurements. This diagnostic is benchmarked to Langmuir probe measurements on the TRIUMF-licensed volume-cusp ion source to determine whether it can replicate the measured electron density and electron temperature as a function of varied operational parameters. The operational parameters are helium gas flow (10-40 SCCM), arc voltage (100-200V), and arc current (1-5A). The measured plasma properties, while different in absolute value, have similar trends for each operational parameter except when varying arc voltage. It is shown that this mismatch as a function of arc voltage is likely due to high energy non-Maxwellian electrons from the cathode sheath, which are not included within the collisional-radiative model.

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.

Nonlinear behaviour of ion acoustic shock waves in a two-electron temperature nonthermal complex plasma

Abstract The nonlinear propagation of dust-ion-acoustic shock waves (DIASWs) in unmagnetized dusty plasma comprising inertial ions, non-Maxwellian electrons with two distinct temperatures, and negatively charged dust is investigated in this article using a different approach based on the Sagdeev pseudopotential theory. The reductive perturbation approach is used to produce the KdVB and mKdVB equations and a comparison of their analytical and numerical solutions is shown. The effects of various parameters consisting of macroscopic non-thermal, ion-kinematic viscosity, etc. that significantly alternate the qualitative properties of DIASW are discussed. Both oscillatory and monotonic natures of the dispersive-diffusive shock wave structures are described in the present study. It has also been concentrated on nonlinear dynamics in such a plasma environment. The findings of this study should aid in understanding the nonlinear dynamics of wave damping and interactions in space and laboratory dusty plasmas, where the most relevant plasma parameters are kinematic viscosity and macroscopic non-thermality.