Kushal Shah
The dispersion relation of an electromagnetic wave in an unmagnetized neutral plasma is well known to be w^2=wp^2+(ck)^2. A modified dispersion relation is presented taking into account the ion restoring force in the transverse direction.
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The propagation of electromagnetic waves in an unmagnetized weakly inhomogeneous cold plasma is examined. We show that the inhomogeneity induces a gauge connection term in wave equation, which gives rise to Berry effects in the dynamics of polarized rays in the post geometric optics approximation. The polarization plane of a plane polarized ray rotates as a result of the geometric Berry phase, which is the Rytov rotation. Also, the Berry curvature causes the optical Hall effect, according to which, rays of left/right circular polarization deflect oppositely to produce a spin current directed a…
We study theoretically the mode conversion and the associated resonant absorption of p-polarized electromagnetic waves into longitudinal plasma oscillations in cold, unmagnetized and stratified plasmas with periodic spatial density variations. We consider sinusoidal density configurations for which the frequency band where mode conversion occurs is well included within a transmission band of the one-dimensional plasma photonic crystal. We calculate the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the plasma, and the spatial distribut…
A theoretical study is presented for the propagation of Dust Ion Acoustic Waves in an unmagnetized four-component plasma, consisting of Maxwellian negative ions, cold mobile positive ions, $κ$-distributed electrons and positively charged dust grains. Based on the characteristics of Sagdeev pseudopotential and phase portraits, three types of nonlinear waves are observed --- solitons, double layers and supersolitons. The conditions for the existence of such nonlinear waves are highly sensitive to the plasma parameters. The results obtained in this study may be of wide relevance in the field of s…
This is the first of a series of papers devoted to the development of the invariant imbedding theory of mode conversion in inhomogeneous plasmas. A new version of the invariant imbedding theory of wave propagation in inhomogeneous media allows one to solve a wide variety of coupled wave equations exactly and efficiently, even in the cases where the material parameters change discontinuously at the boundaries and inside the inhomogeneous medium. In this paper, the invariant imbedding method is applied to the mode conversion of the simplest kind, that is the conversion of $p$-polarized electroma…
It is pointed out that electron thermal fluctuations can couple with the ion acoustic mode in an inhomogeneous plasma to generate a low frequency ion time scale electromagnetic wave. This electromagnetic wave can become unstable if the temperature and density gradients are parallel to each other which can be the case in laser-plasmas similar to stellar cores. The comparisons of the present theoretical model with the previous investigations are also presented. The final result is applied to a classical laser induced plasma for illustration.
Relativistic unmagnetized cloud-plasma interaction is analyzed by performing linear analysis and particle-in-cell simulation. This course consists of an electron-ion cloud injected into a stationary ambient plasma and has long been a favorite topic in laboratory and space plasmas. An oblique electromagnetic instability dominates the unstable spectrum. In the interaction with the generated electromagnetic fields, the cloud electrons are entirely mixed with the ambient ones and form a hot electron population. The velocity of the cloud ions, however, has not changed significantly from the initial…
Optical effects in unmagnetized cold plasmas by a chiral axion factor
在手性MCJF电动力学框架下，通过轴子手性因子在非磁化冷等离子体中恢复磁化等离子体特性，推导出新折射率与传播模式，发现手性因子诱导双折射、负折射及旋光率反转，且不改变Langmuir波色散关系。
Ponderomotive forces in unmagnetized plasmas described by Kappa distribution functions
本研究分析了Kappa分布的无磁场等离子体中电磁波产生的有质动力，发现非热效应对空间部分影响可忽略，但时间因子仅由超热粒子引起，且磁场随偏离热平衡而增强。
This work describes the scientific basis and associated simulation results for the magnetization of an unmagnetized plasma via beat wave current drive. Two-dimensional electromagnetic particle-in-cell simulations have been performed for a variety of angles between the injected waves to demonstrate beat wave generation in agreement with theoretical predictions of the beat-wave wave vector and saturation time, revealing new 2D effects. The simulations clearly demonstrate electron acceleration by the beat waves and resultant current drive and magnetic field generation. The basic process depends e…
The main purpose of this work is the investigation of the influence of electron-positron-ion on the electrostatic wakefields that are driven by intense, short electromagnetic wave packets in a three component unmagnetized plasma. The equations that describes the driven electrostatic wakefield are given in the form of system of nonlinear differential equations. The solution of that system was carried out numerically and the results are displayed graphically.
A relativistic quantum field theory with nontrivial background fields is developed and applied to study waves in plasmas. The effective action of the electromagnetic 4-potential is calculated ab initio from the standard action of scalar QED using path integrals. The resultant effective action is gauge invariant and contains nonlocal interactions, from which gauge bosons acquire masses without breaking the local gauge symmetry. To demonstrate how the general theory can be applied, we study a cold unmagnetized plasma and a cold uniformly magnetized plasma. Using these two examples, we show that …
It is pointed out that the unmagnetized inhomogeneous plasmas can support a low frequency electromagnetic ion wave as a normal mode like Alfven wave of magnetized plasmas. But this is a coupled mode produced by the mixing of longitudinal and transverse components of perturbed electric field due to density inhomogeneity. The ion acoustic wave does not remain electrostatic in non-uniform plasmas. On the other hand, a low frequency electrostatic wave can also exist in the pure electron plasmas. But the magnetic field fluctuations in both electron as well as in electron-ion plasmas are coupled wit…
Interaction of Strong Electromagnetic Waves with Unmagnetized Pair Plasmas
研究强电磁波与无磁化对等离子体的相互作用，发现由非线性参数ε_p决定，当ε_p<1时感应康普顿散射导致脉冲轮廓变窄，当ε_p>1时电磁脉冲驱动相对论性激波。
The spatio-temporal evolution and breaking of relativistically intense wave packets in a cold homogeneous unmagnetized plasma has been studied analytically and numerically. A general expression for phase mixing time scale as a function of amplitude of the wave packet and width of the spectrum has been derived. Results have been compared with the existing formulae in literature. It is shown that phase mixing time scale crucially depends on the relative magnitude of the amplitude and dimensionless spectral width of the wave packet. Finally we have verified our results with respect to both the am…
The three-dimensional instability of two coupled electromagnetic waves in an unmagnetized plasma is investigated theoretically and numerically. In the regime of two-plasmon decay, where one pump wave frequency is approximately twice the electron plasma frequency, we find that the coupled pump waves give rise to enhanced instability with wave vectors between those of the two beams. In the case of ion parametric decay instability, where the pump wave decays into one Langmuir wave and one ion acoustic wave, the instability regions are added with no distinct amplification. Our investigation can be…
The effect of short wavelength quantum electrodynamic (QED) correction on plasma-wave propagation is investigated. The effect on plasma oscillations and on electromagnetic waves in an unmagnetized as well as a magnetized plasma is investigated. The effects of the short wavelength QED corrections are most significant for plasma oscillations and for extraordinary modes. In particular, the QED correction allow plasma oscillations to propagate, and the extra-ordinary mode looses its stop band. The significance of our results is discussed.
The spectrum of electromagnetic waves propagating in a strongly coupled magnetized fully ionized hydrogen plasma is found. The ion motion and damping being neglected, the influence of the Coulomb coupling on the electromagnetic spectrum is analyzed.
In the present analysis we study the self consistent propagation of nonlinear electromagnetic pulses in a one dimensional relativistic electron-ion plasma, from the perspective of nonlinear dynamics. We show how a series of Hamiltonian bifurcations give rise to the electric fields which are of relevance in the subject of particle acceleration. Connections between these bifurcated solutions and results of earlier analysis are made.
The dispersion characteristics of an circularly polarized electromagnetic wave of arbitrary amplitude, propagating in a highly (thermally and kinematically) relativistic plasma, are shown to approach those of a linear wave in an unmagnetized, non-relativistic plasma. Further aided by high relativistic temperatures, the cut-off frequency tends to become negligibly small; as a result, waves with frequencies well below the nominal plasma and the cyclotron frequencies find the plasma to be essentially transparent. This relativistic phenomenon may greatly advance our ability to understand and model…
We consider a recently derived kinetic model for weakly relativistic quantum plasmas. We find that that the effects of spin-orbit interaction and Thomas precession may alter the linear dispersion relation for a magnetized plasma in case of high plasma densities and/or strong magnetic fields. Furthermore, the ponderomotive force induced by an electromagnetic pulse is studied for an unmagnetized plasma. It turns out that for this case the spin-orbit interaction always give a significant contribution to the quantum part of the ponderomotive force.
We study the spatio-temporal evolution of the nonlinear electrostatic oscillations in a cold magnetized electron-positron (e-p) plasma using both analytics and simulations. Using a perturbative method we demonstrate that the nonlinear solutions change significantly when a pure electrostatic mode is excited at the linear level instead of a mixed upper-hybrid and zero-frequency mode that is considered in a recent study. The pure electrostatic oscillations undergo phase mixing nonlinearly. However, the presence of the magnetic field significantly delays the phase-mixing compared to that observed …
A theoretical investigation has been made to study the cylindrical and spherical electron-acoustic shock waves (EASWs) in an unmagnetized, collisionless degenerate quantum plasma system containing two distinct groups of electrons (one inertial non-relativistic cold electrons and other inertialess ultra-relativistic hot electrons) and positively charged static ions. By employing well known reductive perturbation method the modified Burgers (mB) equation has been derived. It is seen that only rarefactive shock waves can propagate in such a quantum plasma system. The effects of degenerate plasma …
The propagation of nonlinear electron- acoustic waves (EAWs) in an unmagnetized collision- less plasma system consisting of a cold electron fluid, superthermal hot electrons and stationary ions is investigated. A reductive perturbation method is employed to obtain a modified Korteweg-de Vries (mKdV) equa- tion for the first-order potential. The small amplitude electron-acoustic solitary wave, e.g., soliton and dou- ble layer (DL) solutions are presented, and the effects of superthermal electrons on the nature of the solitons are also discussed. But the results shows that the weak stationary EA…
Ion Kinetics and Neutron Generation Associated with Electromagnetic Turbulence in Laboratory-scale Counter-streaming Plasmas
本研究利用高阶隐式粒子模拟代码，定量揭示实验室尺度对撞等离子体中电磁湍流对离子动力学的影响机制，解释了非磁化实验结果，磁化场景结论可通过现有实验验证。
Electromagnetic wave propagation through cold collision free plasma is studied using the nonlinear perturbation method. It is found that the equations can be reduced to the modified Kortweg-de Vries equation.
It is well--known that when magnetic monopoles are introduced in plasma equations the propagation of electromagnetic waves is modified. This occurs because of Maxwell equations acquire a symmetrical structure due to the existence of electric and magnetic charge current densities. In this work we study the nonlinear phenomena of ponderomotive forces associated to the presence of magnetic monopoles in a plasma. We generalize the Washimi-Karpman result for the ponderomotive force on electric charges to take into account the symmetrical form of Maxwell equations in the presence of magnetic charges…
Three-wave interactions in plasmas are described, in the framework of kinetic theory, by the quadratic response tensor (QRT). The cold-plasma QRT is a common approximation for interactions between three fast waves. Here, the first-order thermal correction (FOTC) to the cold-plasma QRT is derived for interactions between three fast waves in a warm unmagnetized collisionless plasma, whose particles have an arbitrary isotropic distribution function. The FOTC to the cold-plasma QRT is shown to depend on the second moment of the distribution function, the phase speeds of the waves, and the interact…
Wave Propagation in Periodic Plasma Media: A Semiclassical Approach
本文采用半经典波包近似研究非磁化周期等离子体中的电磁波传播，揭示运动方程中的 Berry 效应及其偏振旋转与 Hall 效应表现，并推广至非均匀等离子体。
Intense radiation field can modify plasma properties, the corresponding refractive index, and lead to such nonlinear propagation effects as self-focusing. We estimate the corresponding effects in pair plasma, both in unmagnetized and strongly magnetically dominated case. First, in the unmagnetized pair plasma the ponderomotive force does not lead to charge separation, but to density depletion. Second, for astrophysically relevant plasmas of pulsar magnetospheres, (and possible loci of Fast Radio Bursts), where cyclotron frequency $ω_B$ dominates over plasma frequency $ω_p$ and the frequency of…
The dynamics of a standing shock front in a Poynting-flux dominated relativistic flow is investigated by using a one-dimensional, relativistic, two-fluid simulation. An upstream flow containing a circularly polarized, sinusoidal magnetic shear wave is considered, mimicking a wave driven by an obliquely rotating pulsar. It is demonstrated that this wave is converted into large amplitude electromagnetic waves with superluminal phase speeds by interacting with the shock when the shock-frame frequency of the wave exceeds the proper plasma frequency. The superluminal waves propagate in the upstream…
The topology, geometry, and angular momentum of cold plasma waves
本文严格研究了冷无磁化等离子体波的拓扑向量丛结构，揭示其电磁波具有拓扑非平凡极化基与角动量分解，为等离子体波提供新全局光滑基及实验相关的准角动量概念。
A theory is proposed that describes mutual conversion of two electromagnetic modes in cold low-density plasma, specifically, in the high-frequency limit where the ion response is negligible. In contrast to the classic (Landau--Zener-type) theory of mode conversion, the region of resonant coupling in low-density plasma is not necessarily narrow, so the coupling matrix cannot be approximated with its first-order Taylor expansion; also, the initial conditions are set up differently. For the case of strong magnetic shear, a simple method is identified for preparing a two-mode wave such that it tra…
In this study we report the effects of an external electromagnetic field on the collective properties of unmagnetized plasmas. The calculations are carried out in the semi-classical approximation, i.e., the electromagnetic field is treated classically and the electrons from a quantum mechanical viewpoint. The results show that the collective modes are damped away more smoothly and in a smaller frequency range than those reported by previous studies. An exponential-like decay of the plasmon frequencies as a function of the external field amplitude is readily observed. We successfully recreate t…
A kinetic theory for electromagnetic ion waves in a cold relativistic plasma is derived. The kinetic equation for the broadband electromagnetic ion waves is coupled to the slow density response via an acoustic equation driven by ponderomotive force like term linear in the electromagnetic field amplitude. The modulational instability growth rate is derived for an arbitrary spectrum of waves. The monochromatic and random phase cases are studied.
We present a quantum kinetic theory for spin-$1/2$ particles, including the spin-orbit interaction, retaining particle dispersive effects to all orders in $\hbar$, based on a gauge-invariant Wigner transformation. Compared to previous works, the spin-orbit interaction leads to a new term in the kinetic equation, containing both the electric and magnetic fields. Like other models with spin-orbit interactions, our model features "hidden momentum". As an example application, we calculate the dispersion relation for linear electrostatic waves in a magnetized plasma, and electromagnetic waves in a …
The effects of linear Landau damping on the nonlinear propagation of dust-acoustic solitary waves (DASWs) are studied in a collisionless unmagnetized dusty plasma with two species of positive ions. The extremely massive, micron-seized, cold and negatively charged dust particles are described by fluid equations, whereas the two species of positive ions, namely the cold (heavy) and hot (light) ions are described by the kinetic Vlasov equations. Following Ott and Sudan [Phys. Fluids {\bf 12}, 2388 (1969)], and by considering lower and higher-order perturbations, the evolution of DASWs with Landau…
Secondary drift-driven instabilities in the presence of a parallel-propagating electromagnetic ion cyclotron wave and cold multi-component ions
通过全动力学粒子模拟和线性理论，研究平行传播EMIC波驱动的次级不稳定性对冷等离子体的影响，发现次级波在低振幅下仍存在，并导致冷质子和氧离子的各向异性加热。
Three-dimensional structure and stability of discontinuities between unmagnetized pair plasma and magnetized electron-proton plasma
本文通过三维PIC模拟研究未磁化正负电子对等离子体与磁化电子-质子等离子体间断面，揭示电磁脉冲、丝化及Rayleigh-Taylor型不稳定性共同导致对等离子体减速压缩，从而为相对论性喷流准直提供关键机制。
The standard theory of plasma emission is based on kinetic couplings between a single beam of energetic electrons and unmagnetized thermal plasmas, involving multi-step nonlinear wave-particle and wave-wave interactions. The theory has not yet been completely verified with fully-kinetic electromagnetic particle-in-cell (PIC) simulations. Earlier studies, greatly limited by available computational resources, are controversial regarding whether the fundamental emission can be generated according to the standard theory. To resolve the controversy, we conducted PIC simulations with a large domain …
Interaction of an intense electromagnetic (EM) beam with hot relativistic plasma is investigated. It is shown that the thermal pressure brings about a fundamental change in the dynamics - localized, high amplitude, EM field structures, not accessible to a cold (but relativisic) plasma, can now be formed under well- defined conditions. Examples of the trapping of EM beams in self-guiding regimes to form stable 2D solitonic structures in a pure e-p plasma are worked out.
Chaos in the dynamics of electromagnetic solitons in relativistic degenerate plasmas
研究电磁孤子在相对论退化等离子体中的非线性相互作用，揭示退化参数对调制不稳定性的影响，并发现其可能引发时空混沌。
Quantum Computing Perspective for Electromagnetic Wave Propagation in Cold Magnetized Plasmas
该研究针对经典麦克斯韦方程组离散方法不适用于量子计算的问题，构建了冷磁化等离子体中麦克斯韦方程组的量子薛定谔表示，开发了量子比特晶格算法（QLA），并通过经典模拟验证了其有效性。
Particle dynamics in nonlinear electromagnetic waves: chaos onset, diffusive heating, and wave surfing
研究强磁化等离子体中带电粒子与超强电磁X模相互作用的动力学，通过Chirikov共振重叠等机制分析混沌起始，用模拟验证理论，发现相空间流再层流化不完全致粒子不同运动状态。
The existence of localized electromagnetic structures is discussed in the framework of the 1-dimensional relativistic Maxwell-fluid model for a cold plasma with immobile ions. New partially localized solutions are found with a finite-difference algorithm designed to locate numerically exact solutions of the Maxwell-fluid system. These solutions are called quasi-solitons and consist of a localized electromagnetic wave trapped in a spatially extended electron plasma wave. They are organized in families characterized by the number of nodes $p$ of the vector potential and exist in a continuous ran…
Linear and nonlinear ion-acoustic waves are studied in a fluid model for non-relativistic, unmagnetized quantum plasma with electrons with an arbitrary degeneracy degree. The equation of state for electrons follows from a local Fermi-Dirac distribution function and apply equally well both to fully degenerate or classical, non-degenerate limits. Ions are assumed to be cold. Quantum diffraction effects through the Bohm potential are also taken into account. A general coupling parameter valid for dilute and dense plasmas is proposed. The linear dispersion relation of the ion-acoustic waves is obt…
A case of moving one-dimensional electromagnetic (EM) solitons formed in a relativistic interaction of a linearly polarized laser light with underdense cold plasma is investigated. The relativistic Lorentz force in an intense laser light pushes electrons into longitudinal motion generating coupled longitudal-transverse wave modes. In a weakly relativistic approximation these modes are well described by a dynamical equation of the generalized nonlinear Schrodinger type, with two additional nonlocal terms [1]. An original analytical solution for a moving EM soliton case is here calculated in an …
Kinetic Simulations of the Filamentation Instability in Pair Plasmas
本研究通过全动力学PIC模拟揭示非磁化成对等离子体中丝状不稳定性形成密度丝及波导式传播的机制，并估算并合时间尺度及其对FRB观测的影响。
The wake field excitation in an unmagnetized plasma by a multi-petawatt, femtosecond, pancake-shaped laser pulse is described both analytically and numerically in the regime with ultrarelativistic electron jitter velocities, when the plasma electrons are almost expelled from the pulse region. This is done, for the first time, in fluid theory. A novel mathematical model is devised that does not break down for very intense pump strengths, in contrast to the standard approach that uses the laser field envelope and the ponderomotive guiding center averaging. This is accomplished by employing a thr…
We study processes at the transition region between hot (rare) and cold (dense) plasma in the collisionless regime. We use a 3-dimensional electromagnetic particle-in-cell (3-D PIC) relativistic code. Motivated by the transition region in the solar atmosphere the temperature and density ratio of the plasmas is chosen as 100 and 0.01, respectively. For better understanding of studied processes we make two types of computations: a) without any interactions among plasma particles (free expansion) and b) with the full electromagnetic interactions. In both the cases we found that the flux of cold p…
Theoretical Analysis and PIC Simulations of Electromagnetic Wakefields Excited by Relativistic Beams in Magnetized Plasmas
本文研究了强磁场中超相对论电子束在冷等离子体通道中激发的纵向和径向尾场，通过发展三维格林函数形式主义并结合PIC模拟，验证了磁场对尾场振荡特性的影响。
(Abridged) This paper addresses the issue of magnetic field generation in a relativistic shock precursor through micro-instabilities. The level of magnetization of the upstream plasma turns out to be a crucial parameter, notably because the length scale of the shock precursor is limited by the Larmor rotation of the accelerated particles in the background magnetic field and by the speed of the shock wave. We discuss in detail and calculate the growth rates of the following beam plasma instabilities seeded by the accelerated and reflected particle populations: for an unmagnetized shock, the Wei…
Using electromagnetic particle-in-cell simulations Winske and Daughton [Phys Plasmas, 19, 072109, 2012] have recently demonstrated that the nonlinear evolution of a wave turbulence initiated by cold ion ring beam is vastly different in three dimensions than in two dimensions. We further analyze the Winske-Daughton three dimensional simulation data and show that the nonlinear induced scattering by thermal plasma particles is crucial for understanding the evolution of lower hybrid/whistler wave turbulence as described in the simulation.
Electromagnetic plasma waves in Big Bounce and Big Crunch cosmologies
本文研究大反弹与大挤压宇宙学背景下冷电子-正电子等离子体中电磁波的精确动力学，发现其分别由Mathieu方程和修正Mathieu方程描述，并揭示宇宙增长或坍缩特征会相似地印刻在波的演化中。
Electromagnetic plasma waves in dark energy cosmology
本文研究了由宇宙学常数主导的暗能量宇宙学等离子体中的电磁波模式，发现该宇宙学效应以含时势形式改变频率响应，并在冷热等离子体中分别求得 Airy 和 Bessel 函数解，特定初始条件导致波长离散化。
Electric fields and waves in the Venus nightside magnetosphere
帕克太阳探测器首次实现金星夜侧磁层高精度电场测量，发现该区域以数赫兹纯静电信号为主、电磁波极少，揭示太阳风与带电离层非磁化天体的相互作用或异于磁化天体，为后续阴影区电场测量技术提供参考。
We analyze the electromagnetic field of a small bunch that uniformly moves in a circular waveguide and transverses a boundary between an area filled up with cold magnetized electron plasma and a vacuum area. The magnetic field is supposed to be strong but finite so the perturbation technique can be applied. Two cases are studied in detail: the bunch is flying out of the plasma into a vacuum, and, inversely, the bunch is flying into the plasma out of the vacuum area of waveguide. The investigation of the waveguide mode components is performed analytically with methods of the complex variable fu…
A new version of the invariant imbedding theory for the propagation of coupled waves in inhomogeneous media is applied to the mode conversion of high frequency electromagnetic waves into electrostatic modes in cold, magnetized and stratified plasmas. The cases where the external magnetic field is applied perpendicularly to the direction of inhomogeneity and the electron density profile is linear are considered. Extensive and numerically exact results for the mode conversion coefficients, the reflectances and the wave electric and magnetic field profiles inside the inhomogeneous plasma are obta…
Buneman instability is often driven in magnetic reconnection. Understanding how velocity shear in the beams driving the Buneman instability affects the growth and saturation of waves is relevant to turbulence, heating, and diffusion in magnetic reconnection. Using a Mathieu-equation analysis for weak cosine velocity shear together with Vlasov simulations, the effects of shear on the kinetic Buneman instability are studied in a plasma consisting of strongly magnetized electrons and cold unmagnetized ions. In the linearly unstable phase, shear enhances the coupling between oblique waves and the …
A rigorous theoretical investigation has been made on electron acoustic wave propagating in unmagnetized collisionless plasma consisting of a cold electron fluid, non-thermal hot electrons and stationary ions. Based on the pseudo-potential approach, large amplitude potential structures and the existence of solitary waves are discussed. The reductive perturbation method has been employed to derive the Korteweg-de Vries (KdV) equation for small but finite amplitude electrostatic waves. An algebraic method with computerized symbolic computation, which greatly exceeds the applicability of the exis…
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