Kinetic Alfven Waves Research Articles

Periodic kinetic Alfvén waves and overtaking between multi-solitons in nonthermal electron–positron–ion plasma

In this paper, the formation of periodic (cnoidal) and solitary kinetic Alfvén waves (KAWs) in nonthermal electron–positron–ion plasma has been illustrated. The KdV equation has been derived by using the reductive perturbation technique. The Sagdeev potential method is used to obtain the solution of KdV equation for examining the dynamics of periodic KAWs. Further, Hirota bilinear method is applied to examine the overtaking process and the expressions of phase shifts of multi-solitons have been determined. Only positive potential kinetic Alfvénic (KA) solitary and periodic waves are evolved in the given plasma environment. The influence of plasma beta, positron density, angle of propagation, nonthermality of electrons and positrons has been investigated on the behaviour of periodic (cnoidal) KAWs. The combined impact of density, nonthermality of electrons as well as positrons has vastly modified the phase shifts of double-as well as triple-solitons. This investigation may have applications for particle acceleration and energy transportation in galactic nucleus and interstellar medium where nonthermal electron and positron pairs exist.

Nonlinear evolution of Kinetic Alfvén Wave and the associated turbulence spectra in laser produced plasmas and laboratory simulation of astrophysical phenomena

This investigation presents the nonlinear interplay between pump wave (Kinetic Alfvén Wave (KAW)) and low-frequency ion acoustic wave (IAW) in the magnetized plasma. The model is developed by taking into account the ponderomotive nonlinearity associated due to the pump KAW. The coupled dimensionless equations (pump and IAW) are solved by adopting numerical simulation technique. The deduced results give the localization and filamentary structures of KAW, which eventually become chaotic with the evolution of time. The fundamental physics governing the dynamics of these two waves is influenced by the plasma beta () parameter; thereby affecting the nature of nonlinearity, dispersive properties and magnetic field amplification. The saturated spectra are analogous to that observed for many astrophysical scenarios for low (Chatterjee et al 2017 Nat. Commun. 8 15970) and high beta (White et al 2019 Nat. Commun. 10 1758; Tzeferacos et al 2017 Phys. Plasmas 24 041404) plasma. This theoretical model outlining the nonlinear interaction can be imperative in understanding the dynamics of magnetic field amplification in various astrophysical scenarios.

Kinetic Alfvén waves in a deuterium-tritium fusion plasma with slowing-down distributed α-particles

The dispersion relation and damping rate of kinetic Alfvén waves (KAWs) in a deuterium-tritium fusion plasma with slowing-down distributed α-particles are investigated using the kinetic theory. The variations of wave frequency and damping rate with respect to the α concentration (nα /n e) and perpendicular wave number (k ⊥) are studied from a numerical way. The results show that the fluctuation of α concentration slightly affects the frequency and damping rate of KAWs at low nα /n e. In addition, the frequency and the damping rate increase as the k ⊥ and the background temperature T e increase. For comparison, the calculations are performed also in the case of α-particles following an equivalent Maxwellian distribution. For a given k ⊥, the value of the frequency obtained in the slowing-down distribution case is smaller than that obtained in the Maxwellian distribution case. Conversely, the value of the damping rate obtained in the slowing-down distribution case is slightly larger than that obtained in the Maxwellian distribution case.

Kinetic Alfven Waves Near a Dissipative Layer

AbstractThe spatial structure of kinetic Alfven waves near a dissipative layer is examined. The type of dispersion for kinetic Alfven waves (KAWs) changes inside the dissipative layer: from ”cold,” when the transverse (across the magnetic shells) wavelength is determined by the electron skin depth in plasma, to ”warm” dispersion, when the wavelength is determined by the ion Larmor radius. The characteristic transverse length of a KAW is complex in the dissipative layer, because it decays strongly when interacting with background plasma electrons. The features of phase shifts between the transverse electromagnetic field components of Alfven oscillations are considered. Phase shift can be used to identify the type of Alfven waves observed by satellites in the vicinity of the dissipative layer. The Alfven wave energy absorption in the dissipative layer can lead to the formation of electron fluxes (with electron energies of 2–5 eV) toward the ionosphere and initiate here the stable auroral red (SAR) arcs. An analytical formula is proposed for determining the density of the electron flux toward the ionosphere and the flux of the energy transferred by them.

Kinetic Alfvén Waves in Space Plasma Environment with κ-electrons

Abstract A resonant instability of kinetic Alfvén waves (KAWs) driven by ion beam is discussed through a theoretical model encompassing Maxwellian background ions and beam ions and non-Maxwellian κ-electrons. The ion beam velocity alone as a source is able to excite the KAWs up to a significant growth. The non-Maxwellian parameter κ impedes the growth of KAWs by restricting the wave unstable region. The effects of other plasma parameters such as propagation angle, temperature of the plasma species, and ion plasma beta on the excitation of KAWs are also examined. The present model can generate waves with frequencies in the range of ≈6.6–51.2 mHz, which are relevant to explaining the observed ultralow frequency waves at auroral ionospheric altitudes. Theoretical model predictions will also be applicable to other planetary environments where ion beams and non-Maxwellian κ-electrons are present.

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Data and processing code for "Tens to hundreds of keV electron precipitation driven by kinetic Alfven waves during an electron injection"

Spacetime Hall-MHD Turbulence at Sub-ion Scales: Structures or Waves?

Abstract Spatiotemporal properties of two-dimensional (2D) Hall-magnetohydrodynamic (MHD) turbulence at intermediate plasma β = 2 are studied by means of Fast Iterative Filtering (FIF), a new technique for the decomposition of nonstationary nonlinear signals. Results show that the magnetic energy at sub-ion scales is concentrated in perturbations with frequencies smaller than the ion-cyclotron (IC) frequency and with polarization properties that are incompatible with both kinetic Alfvén waves (KAWs) and IC waves. At higher frequencies, we clearly identify signatures of both whistler waves and KAWs; however, their energetic contribution to the magnetic power spectrum is negligible. We conclude that the dynamics of 2D Hall-MHD turbulence at sub-ion scales is mainly driven by localized intermittent structures, with no significant contribution of wavelike fluctuations.

The effect of oxygen ions on the stability and polarization of Kinetic Alfvén Waves in the magnetosphere

One of the most striking properties of Kinetic Alfvén Waves (KAW) is that, unlike the also Alfvénic Electromagnetic Ion Cyclotron (EMIC) waves, these waves are right-hand polarized in the plasma frame. In particular, this signature property is key for the identification of KAW from in situ measurements of plasma waves. From the theoretical point of view, both the dispersion relation and the polarization of KAW has been mostly studied in proton–electron plasmas. However, most astrophysical and space plasmas are multi-species, and therefore in these systems the dispersion properties of the KAW may not depend only on the macroscopic parameters of proton and electron distributions, but also on the parameters of heavier ions. Here, using Vlasov linear theory we study the dispersion properties of Alfvénic modes in multi-species plasmas composed by electrons, protons, and O+ ions, with macroscopic plasma parameters relevant to the inner magnetosphere. In consistency with recent observations, our numerical results show that the presence of O+ ions allows the existence of KAW in a wider wave-number range and at smaller wave-normal angles compared to the electron–proton case, but at the same time isotropic O+ ions tend to reduce (or even inhibiting) the growth rates of unstable KAW triggered by anisotropic protons. These results suggest that magnetospheric ions may play an important role on the energy transfer from large macroscopic scales to sub-ionic and electronic scales, especially during intense geomagnetic storms in which O+ ions can dominate the plasma composition in the inner magnetosphere.

Inverse cascade and magnetic vortices in kinetic Alfvén-wave turbulence

A Hamiltonian two-field gyrofluid model for kinetic Alfvén waves (KAWs) in a magnetized electron–proton plasma, retaining ion finite-Larmor-radius corrections and parallel magnetic field fluctuations, is used to study the inverse cascades that develop when turbulence is randomly driven at sub-ion scales. In the directions perpendicular to the ambient field, the dynamics of the cascade turns out to be non-local and the ratio $\chi _f$ of the wave period to the characteristic nonlinear time at the driving scale affects some of its properties. For example, at small values of $\chi _f$ , parametric decay instability of the modes driven by the forcing can develop, enhancing for a while inverse transfers. The balanced state, obtained at early time when the two counter-propagating waves are equally driven, also becomes unstable at small $\chi _f$ , leading to an inverse cascade. For $\beta _e$ smaller than a few units, the cascade slows down when reaching the low-dispersion spectral range. For higher $\beta _e$ , the ratio of the KAW to the Alfvén frequencies displays a local minimum. At the corresponding transverse wavenumber, a condensate is formed, and the cascade towards larger scales is then inhibited. Depending on the parameters, a parallel inverse cascade can develop, enhancing the elongation of the ion-scale magnetic vortices that generically form.

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.

Excitation of kinetic Alfvén waves by streaming ions in a dusty magnetoplasma with generalized (r, q) distribution function

AbstractWe investigate the parallel streaming effects on the dispersion characteristics of a kinetic Alfvén wave (KAW) in a low β dusty magnetoplasma. To analyse the influence of streaming ions obeying generalized (r, q) distribution function, hot and magnetized electrons, and mobile charged dust, a theoretical approach has been used for the instability analysis by employing two potential theories. A linear kinetic dispersion relation of Alfvén waves is derived, whose solutions are used to interpret the numerical and analytical results. The solutions of dispersion relation indicate that the characteristics of KAWs are transformed when generalized (r, q) distribution function is employed instead of its Maxwellian counterpart. We also found that the unstable modes have a strong dependence on spectral indices r and q, dust parameters, and plasma β. For the excitation of KAWs, the streaming velocity has been observed to be within the sub‐Alfvén range, whereas when it extends to the super‐Alfvén range, the growth rates are significantly suppressed. The observations further show that an ambient magnetic field and superthermal particles inhibit the growth of an electromagnetic wave to a significant degree and have a stabilizing effect on the wave mode, whereas an increasing concentration of low‐energy particles contributes to enhancing growth rates.

Persistence of Ion Cyclotron Waves and Stochasticity of Kinetic Alfvén Waves in the Solar Wind

This paper investigates the nature of the physical processes underlying the origin of the Ion Cyclotron Waves (ICWs) and Kinetic Alfvén Waves (KAWs) in the solar wind, by studying their Waiting Time Distributions (WTDs). The results show that ICWs and KAWs do not share common statistical properties: while KAWs independently occur as stochastic, uncorrelated wave packets governed by Poisson statistics, ICWs are highly correlated, thus departing from the Poisson hypothesis. The results based on the WTD analysis may cast more light on the mechanisms actively at work in the generation of the two wave modes. Specifically, while the stochastic character of KAWs may be reminiscent of the random convection-driven jostling of the flux-tube foot-points that generates the Alfvén waves in the lower solar atmosphere, the correlations among the ICW events can be effectively explained on the basis of the persistent nature of the mechanism underlying the local origin of ICWs, namely the proton cyclotron instability. Alternative explanations for the observed distribution of ICW waiting times, based on a piecewise-constant Poisson process involving time-varying rates, are also reported.

Plasma and Field Observations in the Magnetospheric Source Region of a Stable Auroral Red (SAR) Arc by the Arase Satellite on 28 March 2017

AbstractA stable auroral red (SAR) arc is an aurora with a dominant 630 nm emission at subauroral latitudes. SAR arcs have been considered to occur due to the spatial overlap between the plasmasphere and the ring‐current ions. In the overlap region, plasmaspheric electrons are heated by ring‐current ions or plasma waves, and their energy is then transferred down to the ionosphere where it causes oxygen red emission. However, there have been no study conducted so far that quantitatively examined plasma and electromagnetic fields in the magnetosphere associated with SAR arc. In this paper, we report the first quantitative evaluation of conjugate measurements of a SAR arc observed at 2204 UT on 28 March 2017 and investigate its source region using an all‐sky imager at Nyrölä (magnetic latitude: 59.4°N), Finland, and the Arase satellite. The Arase observation shows that the SAR arc appeared in the overlap region between a plasmaspheric plume and the ring‐current ions and that electromagnetic ion cyclotron waves and kinetic Alfven waves were not observed above the SAR arc. The SAR arc was located at the ionospheric trough minimum identified from a total electron content map obtained by the GNSS receiver network. The Swarm satellite flying in the ionosphere also passed the SAR arc at ~2320 UT and observed a decrease in electron density and an increase in electron temperature during the SAR‐arc crossing. These observations suggest that the heating of plasmaspheric electrons via Coulomb collision with ring‐current ions is the most plausible mechanism for the SAR‐arc generation.

Fluid and kinetic aspects of magnetic reconnection and some related magnetospheric phenomena

Magnetic field reconnection plays a key role in determining the magnetic field topology and in the conversion of magnetic energy into kinetic energy in cosmic plasmas. Magnetic reconnection was proposed by solar physicists in an attempt to explain solar flares. The concept of magnetic reconnection was extended to Earth’s magnetosphere to explain auroral substorms. In this review, we first briefly review the classical fluid steady models with small separatrix angle. We then report magnetic reconnection with a large separatrix angle, and the time-dependent multiple X line reconnection (MXR) associated with flux transfer events. The transition from a single X line reconnection to MXR is examined. Global three-dimensional (3-D) magnetic reconnection is reviewed. The particle pressure gradient associated mainly with the electron (ion) off-diagonal pressure tensor terms, $$P_{xy}$$ and $$P_{zy}$$ , is shown to play an important role for electron (ion) dynamics to balance the reconnection electric field ( $$E_{y}$$ ) near the X line. In addition, various plasma waves and instabilities may occur near the ion diffusion and electron diffusion regions, including the upper hybrid drift waves, lower hybrid drift waves, ion-ion beam instability, electron beam instability, whistler waves and kinetic Alfven waves. The layered structure of outflow region of magnetic reconnection is examined. These layered structures include slow shocks, rotation discontinuities, expansion waves and plasma jets. Recent satellite observations of magnetic reconnection in the Earth and planetary magnetospheres are also discussed. The polar cap electric field associated with magnetic reconnection at the Earth's magnetopause and the energy flow in the polar cap region are examined.

Solitary dispersive Alfven wave in a plasma with hot electrons, cold positrons and ions

The dispersion relation and the nonlinear behaviour of dispersive Alfven waves (DAWs) in a plasma, which is composed by hot electrons, cold positrons and ions, are studied from the multi-component fluid theory. It can be indicated from the linear dispersion relation that the coupling of positron acoustic waves with shear Alfven waves results from the effect of the finite ion gyroradius. In our mode, the pressure and the inertia of the positron acoustic wave are, respectively, provided by the hot electrons and the cold positrons, which are different from the ones in a plasma consisting of two-group positrons with different temperatures. Furthermore, the existence and properties of DAW solitons are analysed from the Sagdeev pseudopotential equation, which indicates the existence of super-Alfvenic or sub-Alfvenic solitary DAWs, as well as the amplitude and width of DAW solitons depend on the positron concentration and the electron temperature. When the effects of cold positrons can’t be neglected, there may coexist the compressive and rarefactive DAW solitons. When the concentration of positron is negligibly small, the properties of DAW solitons in our model are similar to the ones of kinetic Alfven wave solitons in a plasma composed by hot electrons and cold ions.

Nonresonant Instability of Kinetic Alfvén Waves with κ-electrons

Abstract A nonresonant instability of kinetic Alfvén waves (KAWs) is studied in a three-component plasma system consisting of background cold ions, an ion beam, and hot electrons with a κ-distribution. The nonresonant KAW instability is produced by the combined sources of ion beam and velocity shear. It is found that the wave excitation by velocity shear alone will give rise to purely growing KAWs, whereas the ion beam velocity alone as a source cannot excite the waves for the considered plasma parameters. It is also observed that the combined sources of ion beam and velocity shear can excite the KAWs in nonresonant instability with finite wave frequency (the mode is not a purely growing mode). Also note that κ-electrons restrict the wave propagation very close to 90°, whereas the Maxwellian electrons permit the wave to propagate a few degrees away from 90°. It is inferred that the presence of κ-electrons shrinks the wave-unstable region of a KAW’s nonresonant instability. The coupling between KAWs and ion-acoustic waves occurs at a lower value of β i for Maxwellian electrons as compared to κ-electrons.

Wave-polarization Analysis of the Alfvénic Slow Solar Wind at Kinetic Scales

Abstract This paper reports the first polarization measurement in the Alfvénic slow solar wind. The normalized magnetic helicity is used as a diagnostic parameter for studying the polarization status of the high-frequency magnetic fluctuations, along with an attempt to identify various wave modes in the solar wind turbulence. Clear evidence for the existence of ion cyclotron waves (ICWs) and kinetic Alfvén waves (KAWs) is also found in the Alfvénic low-speed plasma, robustly supporting the idea that the Alfvénic content of the solar wind fluctuations at fluid scales is the key parameter driving wave generation at kinetic scales. By separating the contributions to helicity from the two modes, it is possible to address the thermodynamical properties of ICWs and KAWs and provide the first direct estimate of their magnetic compressibility. In particular, while ICWs are mainly associated with higher levels of anisotropy and appear to be bounded by the threshold of proton–cyclotron kinetic instability, KAWs (which end up being more compressive than ICWs) are found at lower anisotropies and seem to be limited by the mirror mode instability threshold, extending as well to near the parallel fire hose unstable region. These result are relevant to theories of turbulence and dissipation in the solar wind.