Parametric generation of whistler waves due to the interaction of high-frequency wave beams with a magnetoplasma

The parametric generation of low-frequency whistler waves by a pump wave beam formed by high-frequency whistler waves with close frequencies is studied experimentally. The electromagnetic fields excited by the beats of two co- or counterpropagating high-frequency waves, or by an amplitude-modulated pump are studied. It is shown that the nonlinear currents at the beat (modulation) frequency are generated by a transverse ponderomotive force arising due to the finite width of the high-frequency beam. In this case, the nonlinear azimuthal drift currents enclose the pump beam and can radiate low-frequency whistler waves to the surrounding plasma.     

Nonlinear generation of sheared flows and zonal magnetic fields by electron whistlers in plasmas

The nonlinear generation of shear field and flow in whistler waves is considered. It is shown that a coherent parametric process leads to modulational instability of four waves whistler interaction. Growth rates for the flow/field are compared with published simulation results.     

Efficient spectral and pseudospectral algorithms for 3D simulations of whistler-mode waves in a plasma

Efficient spectral and pseudospectral algorithms for simulation of linear and nonlinear 3D whistler waves in a cold electron plasma are developed. These algorithms are applied to the simulation of whistler waves generated by loop antennas and spheromak-like stationary waves of considerable amplitude. The algorithms are linearly stable and show good stability properties for computations of nonlinear waves over tens of thousands of time steps. Additional speedups by factors of 10–20 (comparing single core CPU and one GPU) are achieved by using graphics processors (GPUs), which enable efficient numerical simulation of the wave propagation on relatively high resolution meshes (tens of millions nodes) in personal computing environment. Comparisons of the numerical results with analytical solutions and experiments show good agreement. The limitations of the codes and the performance of the GPU computing are discussed.     

Electrodynamics and dispersion properties of a magnetoplasma containing elongated and rotating dust grains

The electrodynamics and dispersion properties of a magnetized dusty plasma containing elongated and rotating charged dust grains are examined. Starting from an appropriate Lagrangian for dust grains, a kinetic equation for the dust grain and the corresponding equations of motion are derived. Expressions for the dust charge and dust current densities are obtained with the finite size (the dipole moment) of elongated and rotating dust grains taken into account. These charge and current densities are combined with the Maxwell-Vlasov system of equations to derive dispersion relations for the electromagnetic and electrostatic waves in a dusty magnetoplasma. The dispersion relations are analyzed to demonstrate that the dust grain rotation introduces new classes of instabilities involving various low-frequency waves in a dusty magnetoplasma. Examples of various unstable low-frequency waves include the electron whistler, the dust whistler, dust cyclotron waves, AlfvÉn waves, electromagnetic ion-cyclotron waves, as well as lower-hybrid, electrostatic ion cyclotron, modified dust ion-acoustic waves, etc. Also found is a new type of unstable waves whose frequency is close to the dust grain rotation frequency. The present results should be useful in understanding the properties of low-frequency waves in cosmic and laboratory plasmas that are embedded in an external magnetic field and contain elongated and rotating charged dust grains.     

Dynamics of whistler spheromaks in magnetized plasmas

Recent laboratory experiments [Stenzel et al., Phys. Rev. Lett. 96, 095004 (2006)10.1103/PhysRevLett.96.095004] have demonstrated interesting phenomena of propagating nonlinear whistler structures (spheromaks) and stationary field-reversed configurations, whose magnetic fields exceed the ambient magnetic field strength. Our objective here is to present simulation studies for these nonlinear whistler structures based on the three-dimensional nonlinear electron magnetohydrodynamic equations. The robustness and longevity of the propagating whistler spheromaks found in the experiments are confirmed numerically. Varying the toroidal field of the spheromak in the initial conditions, we find that the polarity and the amplitude of the toroidal field determine the propagation direction and speed of the spheromak. Our simulation results are in excellent agreement with those observed in the laboratory experiments.     

Coupled whistler and ion-acoustic mode propagation in two-electron-temperature plasmas

The nonlinear coupling between whistler and ion-acoustic modes in a plasma having bi-Maxwellian distributed electrons is considered. For stationary propagation, the coupled waves lead to a novel nonlinear structure which has a triple-hump profile for the whistler field intensity. In the critical parameter regime (Δ = 3), only supersonic propagation of the coupled modes is allowed. In other regimes, three integrable cases of the coupled mode propagation have been identified.     

Upconversion of whistler waves by gyrating ion beams in a plasma

A gyrating ion beam, with a ring-shaped distribution in velocity, supports negative energy beam modes near the harmonics of beam gyro-frequency. An investigation of the non-linear interaction of high-frequency whistler waves with the negative energy beam cyclotron mode is made. A non-linear dispersion relation is derived for the coupled modes. It is shown that a gyrating ion-beam frequency upconverts the whistler waves separated by harmonics of beam gyro-frequency. The expression for the growth rate of whistler mode waves has been derived. In Case 1, a high-amplitude whistler wave decays into two lower frequency waves, called a low-frequency mode and a side band of frequency lower than that of pump wave. In Case 2 a high-amplitude whistler wave decays into two lower frequency daughter waves, called the low-frequency mode and whistler waves. Generation mechanism of these waves has application in space and laboratory plasmas.     

Ionization self-channeling of whistler waves in a collisional magnetized plasma

An investigation is made of the self-interaction of whistler waves (whistlers) involving the formation of waveguide channels in a collisional magnetoactive plasma as a result of its additional ionization by the field of the propagating wave. Simplified equations are derived to describe the behavior of the whistler field in a channel of enhanced plasma density in the presence of electron collisions. Self-consistent distributions of the field and the plasma corresponding to steady-state ionization self-channeling of whistlers are obtained by numerically solving the equations for the field together with balance equations for the electron density and energy. Our estimates indicate that this effect can be observed under laboratory conditions. Zh. éksp. Teor. Fiz. 112, 1285–1298 (October 1997)     

Modulation instability of whistler waves

The Karpman and Krushkal criterion has been applied to nonlinear Schrödinger equation derived for whistler waves propagating through magnetoplasma containing parallel electrostatic field. The role of parallel electrostatic field on the frequency spectrum and growth rate of modulational instability has been discussed.     

Whistler mode based explanation for the fast reconnection rate measured in the mit versatile toroidal facility

Despite the widely discussed role of whistler waves in mediating magnetic reconnection (MR), the direct connection between such waves and the MR has not been demonstrated by comparing the characteristic temporal and spatial features of the waves and the MR process. Using the whistler wave dispersion relation, we theoretically predict the experimentally measured rise time (τ(rise)) of a few microseconds for the fast rising MR rate in the Versatile Toroidal Facility at MIT. The rise time is closely given by the inverse of the frequency bandwidth of the whistler waves generated in the evolving current sheet. The wave frequencies lie much above the ion cyclotron frequency, but they are limited to less than 0.1% of the electron cyclotron frequency in the argon plasma. The maximum normalized MR rate R=0.35 measured experimentally is precisely predicted by the angular dispersion of the whistler waves.     

Laboratory modeling of the interaction of electron beams with a magnetoplasma

We present the results of laboratory experiments in which the mechanisms of interaction of electron beams with whistler waves in a magnetoplasma are studied. Different mechanisms of whistler generation during the injection of a modulated electron beam in the plasma are studied, and the mechanism of conversion of the beam kinetic energy to radiation is demonstrated. The processes of whistler wave generation by the modulated beam at the ˇ Cerenkov and Doppler resonances are analyzed in detail. The excitation of whistler waves by means of a nonresonant mechanism of the transition radiation is studied.     

Boundary Effects on Microwave Propagation in a Large Waveguide Containing a Magnetoplasma

Solution of Maxwell's equations for a cold, uniform magnetoplasma bounded by conducting walls shows (i) how plane waves evolve in the space of (?/?c,?p/?c) with (kc/?c) as parameter, and (ii) the range of parameters in which whistler mode propagation without Wieder's fine structure can be expected. In this space, the whistler evolves from an electrostatic mode at low densities, the whistler characteristic appears in a range of densities where the static approximation is invalid, and at still higher densities, residual effects of boundaries show up in the fine structure, as accounted for by J. C. Lee. The asymptotic form of the solution when lateral dimensions are large shows the existence of classes of solutions which are inadmissible because none can be reached along a continuous locus in this space. Effects of finite boundaries on the dispersion characteristic and the interpretation of experimental data are discussed.     

A whistler wave interaction with a density striation: a laboratoryinvestigation of an auroral process

In a laboratory experiment, whistler waves are launched toward a field-aligned density gradient. Characteristic scale length and frequency ratios were carefully scaled to reproduce situations found in the auroral ionosphere. The experiment clearly shows the direct conversion of whistler waves to largely electrostatic lower hybrid waves     

Plasma Maser Theory of Whistler Waves in the Presence of Ion Cyclotron Turbulence

In this paper we consider the plasma maser theory of whistler waves in the presence of ion cyclotron waves in a magnetized plasma. In a plasma with low frequency ion cyclotron turbulence and a high frequency test whistler wave, growth of the whistler wave takes place because of the turbulent bremsstrahlung interaction between the resonant electrons and the modulated electric fields. The growth rate of the whistler wave is calculated and the results discussed.     

Transonic whistler solitons

We consider the coupling of ion-acoustic perturbations with large amplitude electron whistler waves. Transonic envelope whistler solitons having a group velocity near the ion-acoustic speed are found.     

General Schrödinger equation for whistler waves propagating along a magnetic field

The general Schrödinger equation (GSE) for whistler waves with their group velocity directed along an external magnetic field is derived. The “mean” wave vector of the wave beam may be parallel to or have an angle Θ = arccos(2ω/ω_c) with the magnetic field. Applications of GSE to the whistler propagation in density ducts are considered. The results are important for the problem of the self-focusing of whistler waves.     

无碰撞电流片低频电磁模不稳定性：MHD模型

利用含无电阻广义Ohm定律的可压缩磁流体力学(MHD)理论，研究了在具有剪切磁场的无碰撞电流片中低频电磁模不稳定性，假定等离子体压力各向同性，推导出了三维扰动传播波模的色散关系.色散关系的数值求解集中在电流片中间平面(z=0)和半厚度边缘(z=1)上，并分别考虑了二维传播和三维传播，以及不同的离子惯性长度情况.主要结果如下：1)对 于二维扰动传播(k_z=0)的波，在z=0平面上，Alfven波增长率最大，不稳定的波 频率 和波数范围也更宽.离中间平面越远，增长率越小，波数区域越小.同时，随着离子惯性长度 的增大，Alfven波不稳定性的增长率变大.2)对于三维扰动传播(k_z≠0)的波， 哨声是 不稳定的.在电流片中间平面上，哨声有明显的增长率；而在离子惯性区外边，哨声的增长 率还变大.3)在电流片中间(z=0)平面上，低频波主要是电流不稳定性激发的.在离中间 平面较远处，电流、密度和压力的梯度不稳定性变得更重要. 关键词： 无碰撞电流片 磁流体力学 色散关系 不稳定性     

Evolution of basic equations for nearshore wave field

In this paper, a systematic, overall view of theories for periodic waves of permanent form, such as Stokes and cnoidal waves, is described first with their validity ranges. To deal with random waves, a method for estimating directional spectra is given. Then, various wave equations are introduced according to the assumptions included in their derivations. The mild-slope equation is derived for combined refraction and diffraction of linear periodic waves. Various parabolic approximations and time-dependent forms are proposed to include randomness and nonlinearity of waves as well as to simplify numerical calculation. Boussinesq equations are the equations developed for calculating nonlinear wave transformations in shallow water. Nonlinear mild-slope equations are derived as a set of wave equations to predict transformation of nonlinear random waves in the nearshore region. Finally, wave equations are classified systematically for a clear theoretical understanding and appropriate selection for specific applications.     

Nonlinear surface waves and solitons

First a general introduction on the notion of surface waves on solids (types of different waves), a reminder on the simplest familiar nonlinear dispersive model equations, and another on the basic equations of nonlinear elasticity are given. Then attention is focused on the linear surface wave problem. The main properties of nonlinear surface waves in the absence of dispersion are studied next by use of several asymptotic techniques. The additional effects of dispersion are then considered and combined with those of nonlinearity with an emphasis on the case of so-called shear-horizontal surface waves and solitary-wave solutions for envelope signals. Finally, typical nonlocality is introduced for nonlinear Rayleigh surface waves, and general comments on more general two-dimensional (in propagation space) nonlinear strain waves on structures are evoked by way of conclusion.     

Whistler channeling in ducts with enhanced density in a magnetoactive plasma

We study the guided propagation of whistler waves along the density ducts created in a magnetoactive plasma under thermal nonlinear conditions. It is found that the thermal diffusion-driven redistribution of plasma due to electron heating in the quasistatic field of a current loop of fairly large radius leads to the formation of a duct with enhanced density. Based on experimental data and theoretical calculations, it is shown that such a duct can sustain the weakly decaying whistler modes excited by a magnetic-type antenna immersed in it. Radiophysical Research Institute, Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 3, pp. 384–394, March, 1998.