Waves In Magnetized Plasma Research Articles

A Nonlinear PIC Algorithm for High Frequency Waves in Magnetized Plasmas Based on Gyrocenter Gauge Kinetic Theory

AbstractNumerical methods based on gyrocenter gauge kinetic theory are suitable for first principle simulations of high frequency waves in magnetized plasmas. The δf gyrocenter gauge PIC simulation for linear rf wave has been previously realized. In this paper we further develop a full-f nonlinear PIC algorithm appropriate for the nonlinear physics of high frequency waves in magnetized plasmas. Numerical cases of linear rf waves are calculated as a benchmark for the nonlinear GyroGauge code, meanwhile nonlinear rf-wave phenomena are studied. The technique and advantage of the reduction of the numerical noise in this full-f gyrocenter gauge PIC algorithm are also discussed.

Modulational instability of electron-acoustic waves in magnetized plasma in presence of excess superthermal electrons

Modulational instability of finite amplitude electron-acoustic waves along external magnetic field is investigated in plasma composed of inertial cold electrons, hot inertialess superthermal electrons and stationary ions. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schrodinger equation which governs the slow modulation of electron acoustic wave packets. Accounting for effects of hot electron to cold electron number density ratio (α), normalized electron-cyclotron frequency (ω c ) as well as the electron superthermal parameter (κ e ) new regimes for modulational instability of electron acoustic waves are obtained and analyzed. The presence of superthermal electrons modifies conditions for modulational instability to occur, as well as associated threshold and growth rate. Concentration of superthermal electrons (i.e., the deviation from a Maxwellian electron distribution) may control or even suppress modulational instability. In contrast to one-dimensional unmagnetized plasmas, instability growth rate is shown to suppress increasing values of k.

Head-on collision of ion-acoustic solitary waves in magnetized plasmas with nonextensive electrons and positrons

This article presents the first study of the head-on collision of two ion-acoustic solitary waves (IASWs) in magnetized plasmas with nonextensive electrons and positrons using the extended Poincare-Lighthill-Kuo (PLK) method. The effects of the ion gyro-frequency to ion plasma frequency ratio, the positron to ion number density ratio, the electrons temperature to positrons temperature ratio, and the nonextensive parameter q on the phase shifts are investigated. It is shown that these factors significantly modify the phase shifts.

Electrostatic waves in a magnetized plasma with nonextensive distribution

The generalized dispersion relation for warm electrostatic waves in magnetized plasmas is derived in the context of the nonextensive q-distribution of Tsallis statistics. The dispersion relation is expressed as a function of different values of the nonextensive parameter q, which quantifies the degree of nonextensivity of the system. The dispersion relation of cold plasma electrostatic waves is obtained in terms of generalized hypergeometric functions by keeping the lowest order thermal terms. It is shown that Landau damping appears both at the wave frequency and also at cyclotron harmonics and depends on the q-parameter. The combination of warm plasma effects and a magnetic field leads to the existence of Bernstein waves in nonextensive plasmas. In general, the nonextensive distribution significantly alters the dispersion relation for Bernstein waves. For a wave with a frequency close to the upper hybrid frequency, diminishing q gives rise to faster frequency fall-off. Bernstein waves which propagate at frequencies higher than the upper hybrid frequency occupy a decreasing range of frequencies above nearest cyclotron harmonics as q is reduced. In the limit q→1, the warm and cold magnetized plasma electrostatic dispersion relation and also Bernstein dispersion are recovered based on the standard Maxwellian distribution.

Heating of ions by high frequency electromagnetic waves in magnetized plasmas

The heating of ions by high frequency electrostatic waves in magnetically confined plasmas has been a paradigm for studying nonlinear wave-particle interactions. The frequency of the waves is assumed to be much higher than the ion cyclotron frequency and the waves are taken to propagate across the magnetic field. In fusion type plasmas, electrostatic waves, like the lower hybrid wave, cannot access the core of the plasma. That is a domain for high harmonic fast waves or electron cyclotron waves—these are primarily electromagnetic waves. Previous studies on heating of ions by two or more electrostatic waves are extended to two electromagnetic waves that propagate directly across the confining magnetic field. While the ratio of the frequency of each wave to the ion cyclotron frequency is large, the frequency difference is assumed to be near the ion cyclotron frequency. The nonlinear wave-particle interaction is studied analytically using a two time-scale canonical perturbation theory. The theory elucidates the effects of various parameters on the gain in energy by the ions—parameters such as the amplitudes and polarizations of the waves, the ratio of the wave frequencies to the cyclotron frequency, the difference in the frequency of the two waves, and the wave numbers associated with the waves. For example, the ratio of the phase velocity of the envelope formed by the two waves to the phase velocity of the carrier wave is important for energization of ions. For a positive ratio, the energy range is much larger than for a negative ratio. So waves like the lower hybrid waves will impart very little energy to ions. The theoretical results are found to be in good agreement with numerical simulations of the exact dynamical equations. The analytical results are used to construct mapping equations, simplifying the derivation of the motion of ions, which are, subsequently, used to follow the evolution of an ion distribution function. The heating of ions can then be properly quantified in terms of the wave parameters and can be conveniently used to find ideal conditions needed to heat ions by high frequency electromagnetic waves.

Effect of ion temperature on ion-acoustic solitary waves in a magnetized plasma in presence of superthermal electrons

Obliquely propagating ion-acoustic soliatry waves are examined in a magnetized plasma composed of kappa distributed electrons and fluid ions with finite temperature. The Sagdeev potential approach is used to study the properties of finite amplitude solitary waves. Using a quasi-neutrality condition, it is possible to reduce the set of equations to a single equation (energy integral equation), which describes the evolution of ion-acoustic solitary waves in magnetized plasmas. The temperature of warm ions affects the speed, amplitude, width, and pulse duration of solitons. Both the critical and the upper Mach numbers are increased by an increase in the ion temperature. The ion-acoustic soliton amplitude increases with the increase in superthermality of electrons. For auroral plasma parameters, the model predicts the soliton speed, amplitude, width, and pulse duration, respectively, to be in the range of (28.7–31.8) km/s, (0.18–20.1) mV/m; (590–167) m, and (20.5–5.25) ms, which are in good agreement with Viking observations.

Geometric phases of the Faraday rotation of electromagnetic waves in magnetized plasmas

Geometric phases of circularly polarized electromagnetic waves in nonuniform magnetized plasmas is studied theoretically. The variation of the propagation direction of circularly polarized waves results in a geometric phase, which also contributes to the Faraday rotation, in addition to the standard dynamical phase. The origin and properties of the geometric phase are investigated. The influence of the geometric phase to plasma diagnostics using the Faraday rotation is discussed as an application of the theory.

Solitons and double-layers of electron-acoustic waves in magnetized plasma; an application to auroral zone plasma

A theoretical investigation is carried out for understanding the properties of electron-acoustic potential structures (i.e., solitary waves and double-layers) in a magnetized plasma whose constituents are a cold magnetized electron fluid, hot electrons obeying a nonthermal distribution, and stationary ions. For this purpose, the hydrodynamic equations for the cold magnetized electron fluid, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation; modified Zakharov–Kuznetsov (MZK) equation, in the small amplitude regime. The MZK equation is analyzed to examine the existence regions of the solitary pulses and double-layers. It is found that rarefactive electron-acoustic solitary waves and double-layers strongly depend on the density and temperature ratios of the hot-to-cold electron species as well as the nonthermal electron parameter.

Slow packets of electromagnetic waves in magnetized plasma with ferrite grains

The propagation of narrow Gaussian electromagnetic wave packets in the collisionless magnetized plasma with ferrite grains (MPFG) is studied. In this system, in the frequency range close to the frequency of the electron cyclotron resonance, which coincides with the frequency of the ferromagnetic resonance, the dispersion of the electric permittivity (electron subsystem) and magnetic permeability (ferrite grain subsystem) must be taken into account simultaneously. The refractive index η of MPFG can be negative and with increase in frequency becomes positive passing through zero. The strong dispersion of η and the group velocity vg results in the spreading of the wave packets, which propagate with velocity much smaller than the speed of light. Their phase velocity is negative if η<0 and positive if η>0. For η<0, the group velocity can have a maximum at some frequency. The wave packets centered at this frequency are weakly spreading. The existence of slow waves in the frequency range, where η≤0, may be a general property of left handed media.

Experimental Identification of Electromagnetically Induced Transparency in Magnetized Plasma

We report the first experimental identification of the new wave branch at electron cyclotron frequency produced by the injection of a frequency-matched intense pump wave in magnetized plasma [A. G. Litvak and M. D. Tokman, Phys. Rev. Lett. 88, 095003 (2002); G. Shvets and J. S. Wurtele, Phys. Rev. Lett. 89, 115003 (2002)], which is a classical phenomenon analogous to electromagnetically induced transparency (EIT) in quantum systems. By using a frequency-sweep interferometer, we directly detected the dispersion relation of the plasma EIT branch for propagation parallel to the background magnetic field. The bandwidth of the EIT window was correlated with the pump-wave electric field and was found to agree with the theoretical prediction.

Alfvénic rogue waves

It is shown that the nonlinear interaction between the magnetic field-aligned circularly polarized (CP) dispersive Alfvén waves and low-frequency electrostatic perturbations give rise to Alfvénic rogue waves in magnetized plasmas. Our results reveal the left-hand CP Alfvénic wave supports both supersonic and subsonic Alfvénic rogue waves. The latter can propagate for backward wave only. The right-hand CP Alfvénic rouge waves appear on account of the amplitude modulation of the waves by quasi-stationary density modulations. The amplitude of the right-hand CP Alfvénic rogue waves decreases with the increase of the plasma number density, but it increases with the increase of the magnetic field strength. However, the amplitude of the subsonic left-hand CP Alfvénic rogue wave becomes stronger with the excess of the plasma number density, but it shrinks with stronger magnetic field strength. Finally, we briefly discuss the relevance of our investigation to the role of the nonlinear Alfvén waves that power the solar wind.

Statistical Characteristics of Scattered Radiation in Medium With Spatial-temporal Fluctuations of Electron Density and External Magnetic Field

Influence of temporal fluctuations of both electron density and external magnetic field fluctuations on scattered ordinary and extraordinary waves in magnetized plasma is investigated using the ray-(optics) method. Transport equation for frequency fluctuations of scattered radiation has been derived. Broadening of the spatial power spectrum and amplification of the intensity of frequency fluctuation taking into account geometry of the task and the features of turbulent magnetized plasma is analyzed for the anisotropic Gaussian correlation function using the remote sensing data. It is shown that spatial-temporal fluctuations of electron density and external magnetic field, anisotropy and angle of inclination of prolate irregularities relative to the external magnetic field may lead to the exponential amplification of the intensity of frequency fluctuations of scattered electromagnetic waves in the collisional magnetized plasma.

The quantum dusty magnetosonic solitary wave in magnetized plasma

The effects of quantum statistic and quantum diffraction on the weakly two-dimensional fast quantum dusty magnetosonic wave propagating perpendicular to the external magnetic field are investigated by considering the inertialess electron, inertialess ion, and inertial cold dust in the low frequency limit. A Kadomstev-Petviashvili equation is derived for the magnetosonic solitary wave by using reductive perturbation method. The results show that the amplitude of soliton increases with the increasing of quantum diffraction effects of both electrons and ions, while the amplitude of the soliton decreases with the increasing of the quantum statistic effects. By using the numerical investigations, the interaction law of the nontrivial line-solitons with rich web structure in the interaction area among the line-solitons is studied by the Wronskian determinant method, which shows that there is no exchange of the energy, the momentum, and the angular momentum in the interaction.

Gyroaverage effects on nontwist Hamiltonians: Separatrix reconnection and chaos suppression

A study of finite Larmor radius (FLR) effects on E × B test particle chaotic transport in non-monotonic zonal flows with drift waves in magnetized plasmas is presented. Due to the non-monotonicity of the zonal flow, the Hamiltonian does not satisfy the twist condition. The electrostatic potential is modeled as a linear superposition of a zonal flow and the regular neutral modes of the Hasegawa–Mima equation. FLR effects are incorporated by gyro-averaging the E × B Hamiltonian. It is shown that there is a critical value of the Larmor radius for which the zonal flow transitions from a profile with one maximum to a profile with two maxima and a minimum. This bifurcation leads to the creation of additional shearless curves and resonances. The gyroaveraged nontwist Hamiltonian exhibits complex patterns of separatrix reconnection. A change in the Larmor radius can lead to heteroclinic–homoclinic bifurcations and dipole formation. For Larmor radii for which the zonal flow has bifurcated, double heteroclinic–heteroclinic, homoclinic–homoclinic and heteroclinic–homoclinic separatrix topologies are observed. It is also shown that chaotic transport is typically reduced as the Larmor radius increases. Poincare sections show that, for large enough Larmor radius, chaos can be practically suppressed. In particular, changes of the Larmor radius can restore the shearless curve.

The anomalous penetration of intense circularly polarized electromagnetic beam through overdense magnetized plasma

The steady state nonlinear propagation of an intense, circularly polarized electromagnetic beam in an inhomogeneous magnetized plasma has been investigated in paraxial approximation. The laser induces a large oscillatory velocity on electrons, raising their mass and lowering the plasma frequency. Further, rising due to cyclotron resonance effect. The propagation of the electromagnetic waves in magnetized plasma in both the extraordinary and ordinary mode is analyzed. The nonlinearity in dielectric function is considered in presence of external magnetic field due to saturation effects for arbitrary large intensity, which leads to focusing/defocusing of the beam. The focusing effect along with magnetic field helps in the process of anomalous penetration of the beam by enhancing the depletion of the plasma from the axial region. The penetration increases with the incident beam power up to some critical value beyond which it rises abruptly when all electrons have been driven out of the axis. The cyclotron resonance effect awfully supports the laser beam to propagate inside the overdense plasma region. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction applicable for underdense and overdense plasma.

Modulation and suppression of weak Cotton-Mouton effect by Faraday rotation

Polarization of electromagnetic waves in magnetized plasma is studied in conditions, when Cotton-Mouton effect is weak enough as compared with Faraday one. Evolution of polarization state is described by new mathematical approach, namely, by angular variables technique (AVT) which describes evolution of the angular parameters of polarization ellipse in magnetized plasma. The method of consequent approximations is applied, which uses the ratio (Ω ⊥/Ω 3) of Cotton-Mouton and Faraday terms, as a small parameter of a problem and allows obtaining simple analytical expressions for azimuthal and ellipticity angles in frame of the first and second approximations. The phenomenon of ellipticity modulation and suppression by Faraday rotation is revealed, which consists in ellipticity decreasing for stronger Faraday rotation, what makes polarization closer to linear one. Numerical illustration of the phenomenon are presented. It is shown that account of the second-order terms of the method of consequent approximation provides an accuracy better than 1% even in conditions, when small parameter Ω ⊥/Ω 3 achieves the value 1/4.

The many faces of shear Alfvén waves

One of the fundamental waves in magnetized plasmas is the shear Alfvén wave. This wave is responsible for rearranging current systems and, in fact all low frequency currents in magnetized plasmas are shear waves. It has become apparent that Alfvén waves are important in a wide variety of physical environments. Shear waves of various forms have been a topic of experimental research for more than fifteen years in the large plasma device (LAPD) at UCLA. The waves were first studied in both the kinetic and inertial regimes when excited by fluctuating currents with transverse dimension on the order of the collisionless skin depth. Theory and experiment on wave propagation in these regimes is presented, and the morphology of the wave is illustrated to be dependent on the generation mechanism. Three-dimensional currents associated with the waves have been mapped. The ion motion, which closes the current across the magnetic field, has been studied using laser induced fluorescence. The wave propagation in inhomogeneous magnetic fields and density gradients is presented as well as effects of collisions and reflections from boundaries. Reflections may result in Alfvénic field line resonances and in the right conditions maser action. The waves occur spontaneously on temperature and density gradients as hybrids with drift waves. These have been seen to affect cross-field heat and plasma transport. Although the waves are easily launched with antennas, they may also be generated by secondary processes, such as Cherenkov radiation. This is the case when intense shear Alfvén waves in a background magnetoplasma are produced by an exploding laser-produced plasma. Time varying magnetic flux ropes can be considered to be low frequency shear waves. Studies of the interaction of multiple ropes and the link between magnetic field line reconnection and rope dynamics are revealed. This manuscript gives us an overview of the major results from these experiments and provides a modern prospective for the earlier studies of shear Alfvén waves.

A finite-mass fluid electron simulation model for low-frequency electromagnetic waves in magnetized plasmas

A finite-mass fluid electron model has been developed for simulating low-frequency electromagnetic waves in finite-β magnetized plasmas. Here, β is the ratio between plasma and magnetic pressures. It is demonstrated in slab geometry that the model successfully exhibits the linear properties of both the kinetic and inertial Alfvén waves as well as the theoretically predicted collisionless tearing-mode instability.

Quantum effects on the propagation of surface waves in magnetized plasma

The quantum effects on the propagation of surface waves is investigated in semi-bounded magnetized quantum plasmas. The results show that surface oscillations can be propagated due to quantum effects. It is also shown that these quantum effects enhance the propagation velocity. For this purpose, the quantum hydrodynamic (QHD) equations with a magnetic field, using Maxwell’s equations, are used to derive the dispersion relations of transverse electromagnetic surface modes (E-modes). The QHD includes quantum forces involving Fermi electron temperature and quantum Bohm potential. It is found that the external magnetic field which is parallel to the propagation waves has a stronger effect on wave decay in our model than in the classical regime. Beside that, the quantum effects enhance the propagation velocity of these waves.

Supersonic and near-sonic solitary ion-acoustic waves in magnetized plasma

The propagation of large-amplitude solitary ion-acoustic waves in magnetized plasma is analyzed. The problem is solved without assuming plasma quasineutrality within the pulse, and the wave potential is described by Poisson’s equation. Solutions in the form of supersonic and near-sonic solitary waves propagating obliquely to the magnetic field are found. The pulses have several peaks and exist for a discrete set of the wave parameters. The amplitude and oscillation frequency of a solitary wave are determined as functions of the Mach number and the propagation angle with respect to the magnetic field.