Inhomogeneous Plasma Research Articles

Modelling annual scintillation velocity variations of FRB 20201124A

ABSTRACT Compact radio sources exhibit scintillation, an interference pattern arising from propagation through inhomogeneous plasma, where scintillation patterns encode the relative distances and velocities of the source, scattering material, and Earth. In previous work, we showed that the scintillation velocity of the repeating fast radio burst (FRB) FRB20201124A could be measured by correlating burst spectrum pairs, with low values of the scintillation velocity and scattering time-scale suggesting scattering nearby the Earth at $\sim$0.4 kpc. In this work, we have measured the scintillation velocity at 10 epochs spanning 1 yr, observing an annual variation that strongly implies the screen is within the Milky Way. Modelling the annual variation with a 1D anisotropic or 2D isotropic screen results in a screen distance $d_{\mathrm{ l}} = 0.40\pm 0.04$ or $0.46\pm 0.06\,$ pc from the Earth, respectively, possibly associated with material outside of the Local Bubble or the edge of the Orion–Eridanus superbubble. Additional measurements particularly at times of low effective velocity will help probe changes in screen properties, and distinguish between screen models. Where scintillation of an FRB originates in its host galaxy or local environment, these techniques could be used to detect orbital motion, and probe the FRB’s local ionized environment.

The effect of collisions on the rayleigh-taylor instability in magnetized quantum plasma

Rayleigh-Taylor instability occurs at the interface between light and heavy fluids whenever the heavier fluid is accelerated by the light one. An important issue is the stability conditions of these systems. Various parameters such as density difference between two fluids, density inhomogeneity length, magnetic field, viscosity, collision can affect the stabilization or destabilization of the system. So far, some of these factors have been investigated in the fields of classical and quantum physics. This process has also been studied in both linear and nonlinear states. Here we consider a collisional magnetic inhomogeneous quantum plasma. For the inhomogeneity profile of density as an exponential function, we calculated the second ordinary equation for the disturbed velocity. Since the differential equation does not have an analytical solution, we have calculated the growth rate curve using numerical methods and obtained the disturbed velocity profile in the discontinuity. Then the effects of different parameters such as collision, magnetic field, quantum effects, and density difference of two fluids on the system stabilization are studied. The various branches of the instability growth rate curve and its relationship with the turbulent velocity profile in discontinuity are also discussed.

Structural Variations of Dust Acoustic Solitary Waves (DASWs) Propagating in an Inhomogeneous Plasma

This paper presents our theoretical investigations on the structural variations of dust acoustic solitary waves (DASWs) in inhomogeneous unmagnetized plasmas. To study the structural variations of DASWs, we have considered collisionless, hot isothermal, and Boltzmannean distribution for electrons-ions with negatively charged dust grains in weakly inhomogeneous plasmas. We have used the reductive perturbation technique (RPT) in the governing equations of plasmas, derived the modified Korteweg-de-Vries (m‑KdV) equation, and obtained the solitary wave solution. We have considered the appropriate stretched coordinates for space and time variables for the inhomogeneous plasma. This paper investigates the effects of dust particles on ion-acoustic solitary waves' propagation in the inhomogeneous plasma model. We have also included the effect of inhomogeneity parameters on the soliton structures.

Phase finite time singularity: On the dissolution of a surface MHD eigenmode to the Alfvén continuum

Phase mixing is a general mechanism of collisionless damping in magnetized plasmas. In a MHD model, the carrier of phase mixing is the Alfvén wave continuum, which is driven by the plasma inhomogeneity. In this work, we study the non-resonant conversion of a surface MHD eigenmode to the Alfvén continuum. It is shown that the finite-time-singularity of the phase of the surface mode can smear its periodic oscillation and induces the excitation of the local Alfvén waves. This type of mode conversion would enhance the collisionless dissipation of the surface eigenmode, i.e., accelerating its dissolution to the Alfvén continuum. The non-resonant mode conversion and damping mechanism explored here have potential applications to understand the physics of collisionless dissipation of various eigenmodes in magnetized plasmas.

Исследование отражения плоской электромагнитной волны от неоднородного плазменного слоя, расположенного на идеально проводящей плоскости

A method for numerical modelling of the reflection of an electromagnetic wave from a planar plasma layer with an inhomogeneous electron density of particles covered of an ideally conducting plane is proposed in the work. The frequency responses of wave reflection coefficients modules are calculated for various incidence angles and electron density profiles of carriers using the differential sweep method. The paper shows that in the region of plasma resonance the plasma layer with a parabolic profile of charge carrier concentration has the lowest reflection level. The effect of the effective frequency of electron collisions in an inhomogeneous plasma layer on the reflection level was studied in this work.

Exploring ultra-high-intensity wakefields in carbon nanotube arrays: An effective plasma-density approach

Charged particle acceleration using solid-state nanostructures has attracted attention in recent years as a method of achieving ultra-high-gradient acceleration in the TV/m domain. More concretely, metallic hollow nanostructures could be suitable for particle acceleration through the excitation of wakefields by a laser or a high-intensity charged particle beam in a high-density solid-state plasma. For instance, due to their special channeling properties as well as optoelectronic and thermo-mechanical properties, carbon nanotubes could be an excellent medium for this purpose. This article investigates the feasibility of generating ultra-high-gradient acceleration using carbon nanotube arrays, modeled as solid-state plasmas in conventional particle-in-cell simulations performed in a two-dimensional axisymmetric (quasi-3D) geometry. The generation of beam-driven plasma wakefields depending on different parameters of the solid structure is discussed in detail. Furthermore, by adopting an effective plasma-density approach, existing analytical expressions, originally derived for homogeneous plasmas, can be used to describe wakefields driven in periodic non-uniform plasmas.

Self-focusing and defocusing phenomena of super-Gaussian laser beams in plasmas carrying density gradient

Considering nonlinearities due to relativistic mass variation and ponderomotive force driven depression in the electron density, a model is developed for the self-focusing of a super-Gaussian laser beam in inhomogeneous plasmas. Since paraxial ray approximation is not appropriate for the beams of super-Gaussian profile, the formulation is developed based on the moment theory. To have an in-depth understanding of self-focusing and defocusing phenomena and to develop generalized treatment, three different types of plasma density profiles namely linear, tangent and exponential density profiles, are considered and the results are compared. Due to the saturating nature of nonlinear permittivity with laser intensity, the beam is found to undergo periodic focusing because of competition between the diffraction divergence and nonlinear self-focusing effects. The ponderomotive nonlinearity enhances the self-focusing. As the super-Gaussian beam moves into higher density plasma region up to several Rayleigh lengths, stronger self-focusing is achieved and the value of minimum spot size decreases.

Higher order long-wave infrared Bessel beams generating tubular plasma waveguides in the atmosphere

We numerically investigate the nonlinear propagation of long-wavelength, higher order Bessel pulses in the atmosphere. We show that 10 micron higher order Bessel beams can generate more homogeneous plasma channels than their 800 nm counterparts. We utilize 4th-order 10.23 μm Bessel wavepackets to create tunable transient plasma tubes in air, and show that they are well suited for the guiding of THz radiation with exceptionally low losses.

Terahertz Radiation Generation by Hermite-cosh Gaussian and Hollow Gaussian Laser Beams in Magnetized Inhomogeneous Plasmas

Terahertz Radiation Generation by Hermite-cosh Gaussian and Hollow Gaussian Laser Beams in Magnetized Inhomogeneous Plasmas

Broadband electromagnetic emission via mode conversion mediated by stimulated Raman scattering in inhomogeneous plasma

Electromagnetic emission via linear mode conversion from electron plasma waves (EPWs) excited by stimulated Raman scattering (SRS) of an incident laser pulse in inhomogeneous plasma is investigated theoretically and numerically. It is found that the mode conversion can occur naturally in underdense plasma region below the quarter critical density provided that EPWs are generated due to the development of backward SRS when the laser pulse is incident at certain angle with the plasma density gradient. The produced radiation may cover a broad frequency range up to half of the incident laser frequency. The dependence of the radiation conversion efficiency on the laser intensity, incident angle, laser pulse duration, plasma density scale length, and initial electron temperature is analyzed based on one-dimensional particle-in-cell simulation. In two-dimensional geometry, due to the development of sideward SRS, it is found that the mode conversion to occur even at normal incidence of the laser pulse. The radiation frequency, bandwidth, duration, and amplitude can be well controlled by the laser and plasma parameters, suggesting that it may provide a new source of tunable broadband radiation as well as a diagnosis of the development of SRS.

Intense Whistler-mode Waves at Foreshock Transients: Characteristics and Regimes of Wave−Particle Resonant Interaction

Thermalization and heating of plasma flows at shocks result in unstable charged-particle distributions that generate a wide range of electromagnetic waves. These waves, in turn, can further accelerate and scatter energetic particles. Thus, the properties of the waves and their implication for wave−particle interactions are critically important for modeling energetic particle dynamics in shock environments. Whistler-mode waves, excited by the electron heat flux or a temperature anisotropy, arise naturally near shocks and foreshock transients. As a result, they can often interact with suprathermal electrons. The low background magnetic field typical at the core of such transients and the large wave amplitudes may cause such interactions to enter the nonlinear regime. In this study, we present a statistical characterization of whistler-mode waves at foreshock transients around Earth’s bow shock, as they are observed under a wide range of upstream conditions. We find that a significant portion of them are sufficiently intense and coherent (narrowband) to warrant nonlinear treatment. Copious observations of background magnetic field gradients and intense whistler wave amplitudes suggest that phase trapping, a very effective mechanism for electron acceleration in inhomogeneous plasmas, may be the cause. We discuss the implications of our findings for electron acceleration in planetary and astrophysical shock environments.

Influence Of Critical Beam Power On Propagation Dynamics Of q-Gaussian Laser Beams In Isotropic Collisional Plasma

In current work, the beam-width parameter (BWP) equation is reduced to two variables such as q and critical beam power (p 0) which govern the propagation dynamics and intervals of critical beam power p 0 of a q-Gaussian laser beam have been investigated. The non-linear dependence of dielectric function in collisional plasma used herein is primarily because of heterogeneous heating of carriers along the wavefront of the laser beam. The influence of intervals of p 0 is further used to explore propagation dynamics of q-Gaussian laser beam in isotropic, homogeneous and collisional plasma has been studied. The Akhmanov’s parabolic equation approach under WKB (Wentzel-Kramers-Brillouin) and paraxial approximations are used in current work. The results have been found reasonably interesting which are revealed graphically and discussed.

Improving the Resolution of Diagnostics of Inhomogeneous Plasma Media Using Spatial Field Processing with Due Regard to Multipath Effects

Improving the Resolution of Diagnostics of Inhomogeneous Plasma Media Using Spatial Field Processing with Due Regard to Multipath Effects

Kinetic theory of parametric decay instabilities near the upper hybrid resonance in plasmas

Parametric decay instabilities (PDIs) near the upper hybrid resonance layer are studied with a 1D framework. In a uniform plasma, the kinetic nonlinear dispersion relation of PDI is numerically calculated for parameters corresponding to electron cyclotron heating experiments at the ASDEX-U tokamak, in which O-mode radiation was converted to X-mode radiation by reflection from the high-field sidewall. The forward scattering processes driven by X-mode and linearly converted electron Bernstein waves (EBWs) are investigated and found to lead to a primary PDI where the pump waves decay into lower hybrid waves and sideband EBWs. A frequency shift of 930 MHz is obtained for the sideband EBWs in the primary PDIs. Subsequently, the sideband EBWs can decay into a low-frequency ion Bernstein quasi-mode (IBQM) and a secondary EBW, where the dominant forward scattering channel is the first-order IBQM with a frequency close to twice the ion cyclotron frequency. The decay channels obtained by numerical calculation can explain the characteristics of the signal observed in ASDEX-U experiments. The threshold of the pump electric field strength required to excite the primary PDI in the presence of plasma inhomogeneity is also estimated.

Cellular foam-based trickle-bed DBD reactor for plasma-assisted degradation of tetracycline hydrochloride

Non thermal plasma (NTP) is a promising technology for degrading organic pollutants in water/wastewater, in which the transfer of energetic species at the interface between gas discharge and liquid phase is key to improve degradation efficiency. Herein, this work shows the development of an integrated system of dielectric barrier discharge (DBD) plasma and open-cell ceramic foam (CF) for the degradation of tetracycline hydrochloride (TCH, a model antibiotic) in liquid film. Specifically, a bespoke trickle-bed DBD reactor with liquid distributor was developed to enable the formation of uniform liquid film on the surface of the hydrophilic CF strut. Due to the improved mass transfer across the thin liquid film, the trickle-bed DBD reactor with the hydrophilic CF exhibited the comparatively highest TCH removal efficiency (>80%) and energy efficiency (viz., EETCH removal of ∼0.6 g kWh−1) among the systems under investigation such as the glass bead packed DBD. The findings showed that the presence of liquid film was beneficial to the propagation of homogeneous plasma discharge in the CF bed and promoted the mass transfer of active species from plasma discharge to liquid, and thus improved the TCH degradation efficiency. Results from quenching experiments suggested that the electron induced active species (especially O2−) played the important role in degrading TCH rather than electrons.

Saturation of the Filamentation Instability and Dispersion Measure of Fast Radio Bursts

Nonlinear effects are crucial for the propagation of fast radio bursts (FRBs) near the source. We study the filamentation of FRBs in the relativistic winds of magnetars, which are commonly invoked as the most natural FRB progenitors. As a result of filamentation, the particle number density and radiation intensity develop strong gradients along the direction of the wind magnetic field. A steady state is reached when the plasma pressure balances the ponderomotive force. In such a steady state, particles are confined in periodically spaced thin sheets, and electromagnetic waves propagate between them as in a waveguide. We show the following. (i) The dispersion relation resembles that in the initial homogeneous plasma, but the effective plasma frequency is determined by the separation of the sheets, not directly by the mean particle density. (ii) The contribution of relativistic magnetar winds to the dispersion measure of FRBs could be several orders of magnitude larger than previously thought. The dispersion measure of the wind depends on the properties of individual bursts (e.g., the luminosity) and therefore can change significantly among different bursts from repeating FRBs. (iii) Induced Compton scattering is suppressed because most of the radiation propagates in near-vacuum regions.

Effect of Finite Ion Larmor Radius (FLR) Corrections on Thermal Instability of Rotating Radiative Porous Astrophysical Plasma in Interstellar Medium (ISM)

Infinite homogeneous plasma’s thermal instability has been studied in relation to finite ion Larmor radius (FLR) corrections, rotation, and porosity, as well as the impacts of radiative heat-loss function and thermal conductivity. With the aid of a normal mode analysis framework and the necessary difficulty-appropriate linearized perturbation equations, a universal dispersion relation is investigated. For the propagation of transverse waves, this dispersion relationship further condenses for rotation axes parallel to and at right angles to the magnetic field. It is proven that the presence of rotation, porosity, thermal conductivity, and radiative heat-loss function altered the thermal instability criterion. To show how different parameters affect the rate at which the thermal instability grows, numerical calculations have been carried out. We discover that rotation, FLR corrections, and medium porosity stabilised the growth rate of the thermal system in the transverse mode of propagation. The conclusion of this research states that the rotation, porosity, and FLR corrections have an impact on the configuration of dense molecular clouds and star formation.

Structured type III radio bursts observed in interplanetary space

Context. The last few decades have seen numerous studies dedicated to fine structures of type III radio bursts observed in the meter–decameter wavelengths. Most of the explanations of the structured radio emission involve the propagation of electron beams through the strongly inhomogeneous plasma in the low corona. To date, only a few type III bursts with fine structures, observed at hecto–kilometric wavelengths, have been reported. Aims. We report here the existence of numerous structured type III radio bursts observed during the STEREO era by all three WAVES instruments on board STEREO A, B, and Wind. The aim of the study is to report and classify structured type III bursts, and to present the characteristics of their fine structures. The final goal is to try to understand the physical mechanism responsible for the generation of structured radio emission. Methods. In this study we used data from all available spacecraft, specifically STEREO and Wind. We employed 1D density models to obtain the speed of the source of type III radio emission, the electron beam. We also performed a spectral analysis of the fine structures in order to compare their characteristics with the metric–decametric fine structures. Results. The presented similarities of the type III fine structures in the metric to decametric and interplanetary wavelengths indicate that the physical processes responsible for the generation of structured type III radio bursts could be the same, at heights from the low corona to the interplanetary range. We show that the observed structuring and intermittent nature of the type III bursts can be explained by the variation in the level of density fluctuations, at different distances from the Sun.

On the Possibility of Intense Unipolar THz Pulses Formation in Nonhomogeneous Nonequilibrium Nitrogen Plasma Channels

We developed a 3D, fully self-consistent model for analysis of the ultrashort THz unipolar pulse formation accompanied by its amplification in a nonequilibrium plasma channel induced in nitrogen by a femtosecond UV laser pulse. The model is based on a self-consistent numerical solution of the second-order wave equation in cylindrical geometry and the kinetic Boltzmann equation for the electron velocity distribution function (EVDF) at different points of the spatially inhomogeneous nonequilibrium plasma channel. Rapid relaxation of the electron velocity distribution function in the plasma channel results in the amplification of the leading front of the THz pulse only, while its trailing edge is not amplified or even absorbed, which gives rise to the possibility of the formation of pulses with a high degree of unipolarity. The evolution of the unipolar pulse after its transfer from the channel to open free space is analyzed in detail.

Enhanced strong-coupling stimulated Brillouin amplification assisted by Raman amplification.

Higher intensity of strong-coupling stimulated Brillouin scattering (SC-SBS) amplification is achieved by supplementary Raman amplification. In this scheme, a Raman pump laser first amplifies the seed pulse in the homogeneous plasma, and then a SC-SBS pump laser continues the amplification in the inhomogeneous plasma in order to suppress the spontaneous instability of pump lasers. The intensity of the seed laser gets higher and the duration of the seed laser gets shorter than that in the pure SC-SBS scheme with the same incident energy, while the energy conversion efficiency is not significantly reduced. We also found that the SC-SBS amplification is seeded by the leading pulse of Raman amplification. The results obtained from envelope coupling equations, Vlasov simulations, and two-dimensional particle-in-cell simulations agree with each other. This scheme offers a possible way to improve the SC-SBS amplification in experiments.