Superthermal Electrons Research Articles

Inertia of Ionospheric Conductance During Electron Precipitation Events

AbstractUsing the SuperThermal Electron Transport (STET) model coupled with the Super‐thermal Proton Electron Atomic Hydrogen—tRansport in the Ionosphere and Thermosphere (SPEAH‐RIT) codes, we demonstrate that temporal variability of ionospheric conductance is defined by several time scales: the temporal variations of the magnetospheric source, the start time of electron precipitation, and the termination of the corresponding source. In these cases, the time scales are defined by dissipation of energetic electrons and effective recombination processes. The results presented in this paper were applied in the regions of pulsating aurora and polar arcs, demonstrating the fact that ionospheric conductance requires some time to form and decay. These time delays constitute an effective “inertia” in the conductance calculation which is not accounted for in many global models which assume an instantaneous connection between precipitation and conductance. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, impacts magnetosphere‐ionosphere (MI) dynamics on a global scale.

Bifurcation analysis of electron-acoustic waves in electron beam-plasma with suprathermal electrons

It has investigated the properties of nonlinear electron-acoustic waves propagating in a four-component collisionless, unmagnetized plasma. The system consists of cool inertial background electrons of temperature T c , the cool inertial electron beam of temperature T b , hot inertialess suprathermal electrons modeled by a κ-distribution of temperature T h , and ions. The nonlinear modified Korteweg-de Vries-Burgers (mKdV-Burgers) equation that characterizes the electron acoustic waves in such a plasma model is derived. The wave solutions of the resultant mKdV-Burgers equation are investigated using planar dynamical system bifurcation theory. The unperturbed hot, cool, and beam electron densities and the superthermal electron parameter are revealed to have a considerable influence on the nonlinear electron-acoustic traveling waves and the associated electric fields. The system evolves also monotonic shock waves when the dissipation term dominates over the dispersion term. The current model might be useful for understanding the generation of nonlinear electron-acoustic waves in a variety of astrophysical plasma settings, including the Earth's magnetosphere.

Fluid and kinetic studies of tokamak disruptions using Bayesian optimization

When simulating runaway electron dynamics in tokamak disruptions, fluid models with lower numerical cost are often preferred to more accurate kinetic models. The aim of this work is to compare fluid and kinetic simulations of a large variety of different disruption scenarios in ITER. We consider both non-activated and activated scenarios; for the latter, we derive and implement kinetic sources for the Compton scattering and tritium beta decay runaway electron generation mechanisms in our simulation tool Dream (Hoppe et al., Comput. Phys. Commun., vol. 268, 2021, 108098). To achieve a diverse set of disruption scenarios, Bayesian optimization is used to explore a range of massive material injection densities for deuterium and neon. The cost function is designed to distinguish between successful and unsuccessful disruption mitigation based on the runaway current, current quench time and transported fraction of the heat loss. In the non-activated scenarios, we find that fluid and kinetic disruption simulations can have significantly different runaway electron dynamics, due to an overestimation of the runaway seed by the fluid model. The primary cause of this is that the fluid hot-tail generation model neglects superthermal electron transport losses during the thermal quench. In the activated scenarios, the fluid and kinetic models give similar predictions, which can be explained by the significant influence of the activated sources on the runaway dynamics and the seed.

Ion acoustic solitary waves in an adiabatic dusty plasma: Roles of superthermal electrons, ion loss and ionization

Abstract The propagation of dust ion acoustic solitary wave (DIASW) is investigated in the multicomponent dusty plasma with adiabatic ions, superthermal electrons and stationary dust. The reductive perturbation method is employed to derive the damped Korteweg-de Vries (DKdV) equation which describes DIASW. The result reveals that, the adiabaticity of ions significantly modifies the basic features of the DIASW. The ionization effect makes the solitary wave growing, while collisions reduce the growth rate and even lead to the damping. With the increase in ionization cross section $\frac{{\Delta \sigma }}{{{\sigma _0}}}$, ion-to-electron density ratio ${{\delta}_{\rm{ie}}}$ and superthermal electrons parameter $\kappa $, the effect of ionization on DIASW enhances.

Effect of the superthermal electrons on the heat flux through a magnetized sheath

A one-dimensional model, in which the ionization and collision are omitted in the Debye sheath region, is applied to investigate the effect of the superthermal electrons on the heat flux through a magnetized sheath. For different temperatures and concentrations of the superthermal electron, and magnitudes and directions of the magnetic field, the profiles of plasma parameters including ion density and flow velocity perpendicular to the wall, the background and superthermal electron densities, and sheath potential in the presheath region are calculated. The variation of the plasma density and sheath potential drop at the Debye sheath entrance with the superthermal electrons and magnetic field modifies the particle and heat fluxes across the Debye sheath to the material surface. The sheath heat transmission coefficient can increase significantly even for a very small superthermal electron population. The dependence of the sheath heat transmission coefficient on the magnetic field angle decreases with the contribution of the superthermal electron in a strong magnetized sheath. When investigation of the heat flux including the superthermal electrons to a water-cooled W/Cu monoblack for the tokamak divertor, compared to the case of without superthermal electrons, it is found that the increase in both heat flux to the material surface and surface temperature of the material is mainly due to the enhancement of the sheath potential drop caused by the superthermal electrons, but the increase in the latter is not as pronounced as the former.

Interaction of ion acoustic multi-solitons in a magnetised superthermal plasma in the presence of dust

In this investigation, a magnetised plasma consisting of inertial ions fluid, charged immobile dust grains in the background and superthermally distributed electrons is considered to study head-on collision between dust ion acoustic multi-solitons. The extended Poincaré–Lighthill–Kuo (PLK) method is employed for the derivation of two KdV equations. Further, in order to determine the multi-solitons solutions of the two KdV equations, the Hirota bilinear method is used. The phase shifts due to head-on collision of multi-solitons have also been determined. The combined influence of superthermality of electrons, density ratio, magnetic field strength etc. on the characteristics of dust ion acoustic solitons, time evolution and the corresponding phase shifts of multi-solitons has been studied numerically. The findings of this investigation might be of great importance to elucidate and provide a comprehensive framework for the understanding of various nonlinear structures in space and astrophysical environments especially in Saturn’s magnetosphere.

Ion-acoustic solitary waves in Mars’ lower ionosphere

This study suggests that ionic species dynamics generate electrostatic ion-acoustic solitary waves (IASWs) in Mars’ lower ionosphere. It has been determined through observations that the lower ionosphere of Mars, specifically between 200 and 350 km above the surface, is mostly made up of ions like O2+ , O +, and CO2+ , along with superthermal electrons. This study investigates the occurrence, propagation, and properties of IASWs. The derivation of the evolution equation is conducted for waves with a small-but-finite-amplitude. In order to analyze IASWs with large amplitude, the Sagdeev pseudo-potential is obtained. The model predicts the propagation of electrostatic IASWs within an electric field range of 1 to 6 mV/m and a pulse duration period of 0.5 to 4 ms. Fast Fourier analysis of the electric field pulse reveals pulses from 0.8 to 4 kHz.

Dynamic behavior of positron acoustic multiple-solitons in an electron–positron-ion plasma

We explore the dynamic characteristics of positron acoustic multiple-solitons in an unmagnetized plasma containing mobile cold positrons, Kappa-distributed superthermal hot electrons and positrons, and stationary positive ions. This study investigates the overtaking collisional effects, various parametric impacts, and phase shifts in the electron–positron-ion (e-p-i) plasma. Through the reductive perturbation technique, we derived the Korteweg-de Vries (KdV) equation and the modified Korteweg-de Vries (mKdV) equation. The multiple-soliton solutions (MSS) are then obtained using the simplified Hirota method and Cole-Holf transformation. The investigation shows that the amplitudes and widths of multi-solitons decrease with the increasing hot positron concentration but increase with the increasing hot electron index parameter. The results are expected to help us understand the dynamics of waves propagation in the pulsar magnetosphere, the active galactic nuclei, the quasar’s relativistic jet, the inner region of the accretion disk surrounding a black hole, etc.

Superthermal Electron Observations at Mars During the December 2022 Disappearing Solar Wind Event

AbstractOn 26–27 December 2022, Mars experienced an extremely low‐density solar wind stream, which was encountered first by Earth because of the radial alignment of the two planets (i.e., Mars opposition). During this event, two important properties of the ionospheric and magnetospheric states changed significantly in response to the low solar wind ram pressure, as inferred from the superthermal electron observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. The interface between the ionosphere and magnetosphere expanded to thousands of kilometers, outside of the nominal bow shock locations, coinciding with the expansion of the cold planetary ions. Meanwhile, the ambipolar electrostatic potential arising from the ionospheric electron pressure gradient increased from the nominal ∼ −0.7 to ∼ −2 V (relative to the lower ionosphere). This enhanced ambipolar potential likely facilitated the observed ionosphere expansion.

The role of superthermal electrons and positrons on magnetised oscillatory shock waves

The role of superthermal electrons and positrons on magnetised oscillatory shock waves

Statistical Mapping of Magnetic Topology at Venus

AbstractDespite Venus having insignificant intrinsic magnetic fields, the magnetic connectivity between the solar wind and the Venus ionosphere, or magnetic topology, is not as simple as expected and is also important for characterizing the Venus space environment. This study provides a technique combining superthermal electron energy and pitch angle distributions to infer up to 6 subtypes of magnetic topology at Venus. This enables us to determine magnetic topology with automated procedures using the Venus Express (VEx) observations from May 2006 to November 2014. We find that the draped topology (both ends of a field line not connected to the collisional ionosphere) is the dominant topology in the near‐Venus space environment, >70%, except at low altitudes close to the ionosphere. The open (a field line connected to both the solar wind and the collisional ionosphere) and closed (a field line connected only to the collisional ionosphere) topologies make up 20%–30% on average of the magnetotail and up to 50% at low altitudes. This study provides the first characterization of the statistical distributions of different magnetic topologies at Venus.

The Role of Plasmasphere in the Formation of Electron Heat Fluxes

AbstractPlasmasphere plays an important role in the magnetospheric physics, defining many important inputs to the ionosphere from the middle to the auroral latitudes. Among them are electron thermal heat fluxes resulting from the Coulomb interaction of superthermal electrons (SE) and cold plasmaspheric electrons. These fluxes define the electron temperature at the upper ionospheric altitudes and are the input to the global ionospheric modeling networks. As was previously found from the calculation of lower energy SE and thermal heat fluxes, the knowledge of field‐aligned cold plasma distribution in the plasmasphere is a very sensitive parameter that introduces the most uncertainties in the calculation of these values. To verify the previously used SuperThermal Electron Transport code assumptions regarding plasmaspheric field‐aligned density structure ∼[B(s)/Bo]a, we used the latest version of 3D plasmaspheric model developed by Pierrard, Botek, and Darrouzet (2021, https://doi.org/10.3389/fspas.2021.681401). Such an assumption is found to be very reasonable in the calculations of electron thermal heat fluxes entering upper ionospheric altitudes and the associated electron temperature formation for the two selected dayside and nightside electron precipitation events driven by whistler‐mode wave activity.

On the Existence of Subsonic Solitary Waves Associated with Reconnection Jets in Earth’s Magnetotail

The Magnetospheric Multiscale Spacecraft (MMS) has detected the signature of electrostatic solitary waves (ESWs) occurring in the reconnection jet site of the Earth’s magnetotail (Liu et al.). These observations have motivated us to explore the mechanism underlying the formation of fast- and slow-mode ion-acoustic solitary waves in the magnetotail region. To this end, we have formulated a three-component magnetized plasma model consisting of nonthermal electrons and two cold ion beams streaming parallel and antiparallel to the magnetic field, respectively. In this work, we have examined the existence conditions for ion-acoustic subsonic waves in a suprathermal space plasma comprising two counterstreaming (drifting) ion beams interacting with a suprathermal electron background. An exact (nonperturbative) nonlinear technique has been adopted to examine the role of the beam velocity and the spectral index on the evolution of subsonic waves. Linear analysis reveals that subsonic waves are unstable when the beam velocity is lower than a threshold value; hence in this regime, only conventional supersonic (fast) waves are formed. On the other hand, when the beam velocity exceeds the threshold, either supersonic or subsonic waves may exist. The combined impact of the beam velocity and electron superthermality on the characteristics of subsonic solitary waves has been analyzed. Our results are shown to be in good agreement with observations of slow ESWs by the MMS spacecraft. Our findings will help to unfold the so-far unexplored dynamical characteristics of subsonic waves that may occur in the reconnection site of Earth’s magnetotail.

Ion acoustic solitons at the acoustic speed in a warm negative ion plasma with superthermal electrons

Using the Sagdeev pseudopotential method, the existence of Korteweg–de Vries (KdV) and non-KdV solitons is investigated in a negative ion plasma comprising adiabatic positive and negative ions and kappa distributed electrons. For some plasma parameter values, the plasma model supports the coexistence of solitons of both polarities. Positive KdV solitons coexist with negative non-KdV solitons at low values of negative to positive ion density ratio, and positive non-KdV solitons coexist with negative KdV solitons at higher values. There is therefore a switch in polarity between positive KdV and negative KdV solitons at a critical value of negative to positive ion density ratio and a switch in polarity between negative non-KdV and positive non-KdV solitons at the same point. At the critical point, there is no soliton at the acoustic speed, although there is coexistence at larger Mach numbers. This confirms that the existence of a soliton at acoustic speed is not a necessary condition for the coexistence of solitons of both polarities. When electrons are strongly non-thermal and the ion temperatures are important, the coexistence region vanishes and the non-KdV solitons disappear with it. It was also found that there is a forbidden region in terms of negative (positive) ion temperatures when the negative (positive) ion temperature increases with the other plasma parameters held fixed.

Simulating Electron Distribution Function in the Pulsating Aurora Using Particle and Wave Data of ARASE Satellite

AbstractDecades lasting research on the pulsating aurora suggested that this phenomenon forms as result of interactions between the magnetospheric keVs electrons and whistler‐mode chorus waves. Arase satellite observation reported the direct evidence for this process confirming in situ measurement of highly correlated precipitated electrons and chorus wave activity. This paper presents the theoretical analysis of this observational event based on the SuperThermal Electron Transport (STET) code that simulates the highly dynamic environment of measured waves and particle data. Specifically, the STET code simulated results confirms the delicate loss‐cone observation results of this mission and further reveals the broader energy range of precipitated electron fluxes that was not measurable by Arase satellite.

Head-on collision of ion-acoustic (modified) Korteweg–de Vries solitons in Saturn's magnetosphere plasmas with two temperature superthermal electrons

In view of the recent observations by plasma science-spacecraft-voyager and Cassini plasma spectrometer of Saturn's magnetosphere, the interaction between two counter-propagating ion-acoustic (IA) solitons is studied in an unmagnetized plasma consisting of warm adiabatic ions in addition to hot and cold electrons following kappa distribution. The head-on collision of the IA solitons is investigated using the extended Poincare–Lighthill–Kuo technique. Since this model supports both compressive and rarefactive solitons, therefore, the soliton collisions for both Korteweg–de Vries (KdV) and the modified KdV (mKdV) equations are investigated. The corresponding phase shifts after the collision for both these equations are also derived and examined. Furthermore, the effects of different plasma parameters (corresponding to Saturn's magnetosphere), including superthermality, density, and temperature on the colliding soliton profiles and their phase shifts, are examined. It is concluded that the phase shift is smaller when both hot and cold electrons are Maxwellian by comparison with the superthermal case.

Low-frequency nonlinear ion-acoustic cnoidal waves in a superthermal plasma with a monoenergetic electron beam

This study analyzes the behavior of nonlinear electrostatic ion-acoustic cnoidal waves (IACWs) in a magnetoplasma characterized by two distinct temperatures of superthermal electrons and a monoenergetic electron beam. For this purpose and based on fluid theory, the reductive perturbation technique is applied to reduce the basic equations to a third-order Korteweg-de Vries (KdV) equation. Under certain conditions, the KdV equation can be used for modeling symmetric CWs; when these conditions are not met, it is replaced by a Kawahara equation to describe these waves correctly. The symmetric IACWs features are examined in detail to determine the effect of pertinent plasma parameters. This study may help model nonlinear structures in astrophysical and space plasmas and understand the mechanism of CWs in the plasma sheath region.

Oblique Arbitrary Amplitude Dust Ion Acoustic Solitary Waves in Anisotropic Non-Maxwellian Plasmas with Kappa-Distributed Electrons

In this paper, we investigate the behavior of dust ion acoustic solitary waves (DIASWs) with arbitrary amplitudes in a magnetized anisotropic dusty plasma that includes inertial hot ion fluid, electrons following a Kappa distribution, and negatively charged dust particles in the background. An ambient magnetic field aligns with the x-direction, while the wave propagation occurs obliquely to the ambient magnetic field. In the linear regime, two distinct modes, namely fast and slow modes, are observed. We employ the Sagdeev pseudo-potential method to analyze the fundamental properties of arbitrary amplitude DIASWs. Additionally, we examine how various physical parameters influence the existence and characteristics of symmetric planar dust ion acoustic solitary structures (DIASs). The characteristics of the solitary structures are greatly influenced by the dust concentration, the electrons superthermality (spectral) index, the obliquity parameter, the magnetic field, the parallel ion pressure and the perpendicular ion pressure. The results show that the amplitude and width of both compressive and rarefactive DIASWs are sensitive to the degree of electron superthermality and dust concentration. Additionally, it is shown that the propagation features of DIASWs are highly affected by the parallel component of ion pressure as compared to perpendicular component of ion pressure.

Interaction of Schamel type solitary waves with superthermal trapped electrons

The expanded Poincar'e-Lighthill-Kuo approach is used to explore the collision of Schamel type ion acoustic solitary waves. The phase shift, the most crucial characteristic, is calculated using specific solutions on the basis of the Schamel type Korteweg-de Vries equations. It has been revealed that, in given regime of physically acceptable conditions, the effects of electron confinement and superthermality have a significant influence in altering the phase shift. The results will be a valuable contribution to ongoing research on plasma waves interactions as well as to inquiries into a number of laboratory plasma experiments.

Electron beam driven ion-acoustic solitary waves in plasmas with two kappa-distributed electrons

Formation and the basic features of arbitrary amplitude ion-acoustic solitary waves (IASWs) in a plasma consisting of warm positive ions, two kappa-distributed electrons and an electron beam are investigated by using the Sagdeev pseudopotential approach. It is shown that the soliton existence domain (Mach number limits) sensitively depends on temperature of ions, spectral index of cool electrons and concentration of hot electron species while spectral index of hot electrons, hot-to-cool electron temperature ratio and also concentration of electron beam do not considerably affect this domain. It is also found that temperature of electron beam only affect the existence domain of rarefactive solitons. Furthermore, it is shown that considered plasma medium supports the coexistence of positive and negative IASWs. Moreover, effect of different plasma parameters such as hot-to-cool electron density ratio, ion-to-cool electron temperature ratio, beam-to-ion density ratio, hot-to-cool electron temperature ratio and superthermality index of electron species on the basic features of positive and negative IASWs is investigated numerically. Finally, the effect of plasma parameters on the parametric regime of coexistence of compressive and rarefactive IASWs is studied and, for example, effect of temperature of positive ions and number density of hot electrons on polarity of IASWs is numerically investigated.