Parametric excitation of surface waves at the boundary between a magnetized plasma and a metal

A study is made of the parametric excitation of potential surface waves propagating in a planar plasma-metal waveguide structure in a magnetic field perpendicular to the plasma-metal boundary. An external, spatially uniform, alternating electric field at the second harmonic of the excited wave is used as the source of parametric excitation. A set of equations is derived that describes the excitation of surface waves due to the onset of decay instability. Expressions for the growth rates in the linear stage of instability are obtained, and the threshold amplitudes of the external electric field above which the parametric instability can occur are found. Analytic expressions for the saturation amplitudes are derived with allowance for the self-interaction of each of the excited waves and the interaction between them. The effect of the plasma parameters and the strength of the external magnetic field on the saturation amplitude, growth rates, and the threshold amplitudes of the pump electric field are analyzed.     

Electromagnetic wave in a relativistic magnetized plasma

Results are presented from a theoretical investigation of the dispersion properties of a relativistic plasma in which an electromagnetic wave propagates along an external magnetic field. The dielectric tensor in integral form is simplified by separating its imaginary and real parts. A dispersion relation for an electromagnetic wave is obtained that makes it possible to analyze the dispersion and collisionless damping of electromagnetic perturbations over a broad parameter range for both nonrelativistic and ultrarelativistic plasmas.     

Temporal discrimination in a long operant chamber

Pigeons were placed in a long chamber equipped with one key and feeder at each end side and one key and houselight at the middle. To obtain food the birds had to choose one side key after a short signal and the other side key after a long signal. The signals consisted of the illumination of the center key and the houselight and were initiated by a peck at the center key. The chamber had sensitive floor panels that enabled us to measure the location of the bird during the signals. In Experiment 1, after the birds learned the discrimination we reversed the assignment of keys to signals. In Experiment 2, we examined performance on two pairs of discriminations holding the same ratio. In Experiment 3, after the pigeons learned to discriminate two signals, we changed the duration of the long signal. The results showed that (a) the birds' motion during the signal was highly stereotypical, i.e. the birds moved to the short side, waited a few seconds, and then departed to, and stayed on the long side; (b) this motion pattern predicted the results of generalization tests with novel durations; (c) the mean of the times of departure from the short side approached its steady state values quicker than the standard deviation and consequently superposition of behavioral measures became stronger with training; (d) only the duration of the short signal influenced significantly the moment the birds departed from the short side; finally (e) the times of arrival at and departure from the short side were positively correlated, but the times of arrival and residence at the short side were negatively correlated.     

Theory of heat transport in a magnetized high-temperature plasma

The transport of charged particles across a strong magnetic field with a small random component is studied in the double diffusion approximation. It is shown that the density of the particles whose initial distribution is stretched along the field satisfies a subdiffusion equation with fractional derivatives. A more general initial particle distribution is also considered, and the applicability of the solutions obtained is discussed.     

Collisionless expansion of a plasma with doubly charged ions in a rarefied magnetized plasma

The collisionless interaction between an expanding cylindrical plasma cloud containing singly and doubly charged ions and a magnetized background plasma is investigated numerically using a method combining the kinetic and hydrodynamic approaches. The results presented were obtained from simulations carried out under conditions corresponding to active space experiments on the expansion of plasma clouds in the Earth’s ionosphere.     

Scalar equation for wave beams in a magnetized plasma

A heuristic procedure is proposed for deriving quasi-optical equations for wave beams in anisotropic gyrotropic media with allowance for aberrations, spatial dispersion, and absorption. To solve such equations numerically, a method is developed that generalizes the operator exponent method. The applicability limits of the aberration-free approximation for simulating the propagation of beams in absorbing media are determined. Numerical examples of the propagation of beams in the vicinity of the electron cyclotron resonance in plasmas in actual devices are presented.     

Nonlinear dynamics of drift structures in a magnetized dissipative plasma

A study is made of the nonlinear dynamics of solitary vortex structures in an inhomogeneous magnetized dissipative plasma. A nonlinear transport equation for long-wavelength drift wave structures is derived with allowance for the nonuniformity of the plasma density and temperature equilibria, as well as the magnetic and collisional viscosity of the medium and its friction. The dynamic equation describes two types of nonlinearity: scalar (due to the temperature inhomogeneity) and vector (due to the convectively polarized motion of the particles of the medium). The equation is fourth order in the spatial derivatives, in contrast to the second-order Hasegawa-Mima equations. An analytic steady solution to the nonlinear equation is obtained that describes a new type of solitary dipole vortex. The nonlinear dynamic equation is integrated numerically. A new algorithm and a new finite difference scheme for solving the equation are proposed, and it is proved that the solution so obtained is unique. The equation is used to investigate how the initially steady dipole vortex constructed here behaves unsteadily under the action of the factors just mentioned. Numerical simulations revealed that the role of the vector nonlinearity is twofold: it helps the dispersion or the scalar nonlinearity (depending on their magnitude) to ensure the mutual equilibrium and, thereby, promote self-organization of the vortical structures. It is shown that dispersion breaks the initial dipole vortex into a set of tightly packed, smaller scale, less intense monopole vortices-alternating cyclones and anticyclones. When the dispersion of the evolving initial dipole vortex is weak, the scalar nonlinearity symmetrically breaks a cyclone-anticyclone pair into a cyclone and an anticyclone, which are independent of one another and have essentially the same intensity, shape, and size. The stronger the dispersion, the more anisotropic the process whereby the structures break: the anticyclone is more intense and localized, while the cyclone is less intense and has a larger size. In the course of further evolution, the cyclone persists for a relatively longer time, while the anticyclone breaks into small-scale vortices and dissipation hastens this process. It is found that the relaxation of the vortex by viscous dissipation differs in character from that by the frictional force. The time scale on which the vortex is damped depends strongly on its typical size: larger scale vortices are longer lived structures. It is shown that, as the instability develops, the initial vortex is amplified and the lifetime of the dipole pair components-cyclone and anticyclone-becomes longer. As time elapses, small-scale noise is generated in the system, and the spatial structure of the perturbation potential becomes irregular. The pattern of interaction of solitary vortex structures among themselves and with the medium shows that they can take part in strong drift turbulence and anomalous transport of heat and matter in an inhomogeneous magnetized plasma.     

Radiation from a pulsed dipole source in a moving magnetized plasma

The problem of radiation from a pulsed dipole source in a moving magnetized plasma described by a diagonal permittivity tensor is considered. An exact solution describing the spatiotemporal behavior of the excited electromagnetic field is obtained. The shape of an electromagnetic pulse that is generated by the source and propagates at different angles to both the direction of the external magnetic field and the direction of plasma motion is investigated. It is found that even nonrelativistic motion of the plasma medium can substantially influence the parameters of radiation from prescribed unsteady sources.     

Escape of electron Langmuir waves from a magnetized plasma

A study is made of electromagnetic oscillations of a plasma in open field line geometry (open magnetic devices). The oscillations that propagate from the critical surface and are originally of the nature of the electron Langmuir waves are shown to continuously change their nature and to escape from the plasma into vacuum in the form of electromagnetic waves. This phenomenon may give rise to wave energy losses from a thermodynamically nonequilibrium (unstable) plasma, e.g., a plasma penetrated by charged particle beams.     

Wakefield excitation by a relativistic electron bunch in a magnetized plasma

The excitation of a wake wave by a relativistic electron beam in an unbounded magnetized plasma and a plasma waveguide is studied theoretically. It is shown that, in a waveguide partially filled with a plasma, the energy that the electrons of the accelerated beam can gain is 37 times higher than the energy of the electrons of the beam generating wakefield.     

Dust-acoustic solitary waves in a four-component adiabatic magnetized dusty plasma

Theoretical investigation has been made on obliquely propagating dust-acoustic (DA) solitary waves (SWs) in a magnetized dusty plasma which consists of non-inertial adiabatic electron and ion fluids, and inertial negatively as well as positively charged adiabatic dust fluids. The reductive perturbation method has been employed to derive the Korteweg-de Vries equation which admits a solitary wave solution for small but finite amplitude limit. It has been shown that the basic features (speed, height, thickness, etc.) of such DA solitary structures are significantly modified by adiabaticity of plasma fluids, opposite polarity dust components, and the obliqueness of external magnetic field. The SWs have been changed from compressive to rarefactive depending on the value of μ (a parameter determining the number of positive dust present in this plasma model). The present investigation can be of relevance to the electrostatic solitary structures observed in various dusty plasma environments (viz. cometary tails, upper mesosphere, Jupiter’s magnetosphere, etc.).     

Electromagnetic oscillations near the critical surface in a magnetized plasma

It is shown that, in a plasma whose density varies across the magnetic field lines, electromagnetic oscillations that are localized near the critical surface can exist. Such oscillations can be excited spontaneously in a nonequilibrium plasma of closed magnetic confinement systems.     

Some features of the stochastic particle dynamics in a magnetized plasma

A study is made of the dynamics of particles interacting with electromagnetic field fluctuations in a plasma in the presence of a magnetic field. Possible mechanisms for the onset of anomalous transport and its suppression by applying a radial electrostatic field are analyzed. Estimates of the diffusion coefficient are proposed based on the calculations of particle trajectories.     

Spectra of langmuir waves in a magnetized plasma with low-frequency turbulence

A study is made of the formation of the spectra of Langmuir waves excited as a result of the development of beam-plasma instability in a collisionless magnetized plasma with low-frequency turbulence. Equations are derived that describe the dynamics of the formation of spectra in the quasilinear statistical approximation.The equations obtained account for small-and large-angle scattering of the electron-beam-excited waves by given background plasma density fluctuations. The scattering of Langmuir waves leads to the redistribution of their energy in phase space and, under appropriate conditions, to the appearance of a characteristic dent in the wave spectra in the frequency range where the spectral intensity is maximum. Numerical simulations carried out for plasma parameters typical of the polar cap of the Earth’s magnetosphere help to explain the shape of the spectra of Langmuir waves that were recorded by the Interball-2 satellite when it was flying through this magnetospheric region.     

Rayleigh-Taylor instability in quantum magnetized viscous plasma

Quantum effects on Rayleigh-Taylor instability of stratified viscous plasmas layer under the influence of vertical magnetic field are investigated. By linearly solving the viscous QMHD equations into normal mode, a forth-order ordinary differential equation is obtained to describe the velocity perturbation. Then the growth rate is derived for the case where a plasma with exponential density distribution is confined between two rigid planes. The results show that, the presence of vertical magnetic field beside the quantum effect will bring about more stability on the growth rate of unstable configuration for viscous plasma, which is greater than that of inviscous plasma.     

Electrostatic solitary structures in a magnetized nonextensive plasma with q-distributed electrons

A rigorous theoretical investigation has been made of obliquely propagating electrostatic solitary structures in a magnetized plasma, taking into account the effect of nonextensive electrons. By employing the reductive perturbation method, the basic characteristics of obliquely propagating ion-acoustic (IA) solitary waves (SWs) in a cold magnetized electron-ion plasma (consisting of inertial ions and noninertial q-distributed electrons) have been addressed. The Korteweg-de Vries equation is derived and its numerical solution is obtained. It has been shown that the effects of electron nonextensivity and external magnetic field significantly modify the natures of the small but finite-amplitude IA SWs. The present analysis may be useful to understand and demonstrate the dynamical properties of IA SWs in different astrophysical and cosmological scenarios (viz. stellar polytropes, hadronic matter, quark-gluon plasma, protoneutron stars, dark-matter halos, etc.).     

Electromagnetically induced transparency in a magnetized plasma during oblique propagation of radiation

The parametric effect of electromagnetically induced transparency (EIT) is studied in the case of quasi-transverse propagation of an extraordinary wave in the vicinity of the upper hybrid resonance in a cold plasma. The question is investigated of whether the waves that propagate in a smoothly inhomogeneous medium (from the transparency region in the vicinity of the upper hybrid resonance into vacuum or in the opposite direction) can reach the EIT region. The features of the quasi-transverse propagation of an extraordinary wave at the electron cyclotron resonance frequency in the quasi-EIT regime are also considered. It is shown that, in this situation, the parametric effects modify the polarization of the wave, with the result that its absorption increases substantially (by one to two orders of magnitude).     

Decay instability of a laser pulse propagating in a transverse direction in a magnetized plasma

The decay instability of a lser pulse propagating across an external magnetic field in a subscritical plasma is investigated analytically and numerically. It is shown that, when the relaxation of the pulse is taken into account, the hydrodynamic growth rate of the decay instability is slower than that obtained earlier in the constant-amplitude pump wave approximation. The results of numerical simulations by a particle-in-cell method demonstrate that an increase in the amplitude of the parametrically excited waves is accompanied by a decrease in their group velocity; in this case, up to 85% of the laser energy is converted into the energy of the plasma particles. It is found that, under resonance conditions, the magnetic field acts to increase the energy of the accelerated ions that escape from the plasma slab through its front boundary.     

Formation of electrode sheaths during the acceleration of a magnetized plasma

A study is made of the motion of a plasma with a frozen-in magnetic field along the electrode surfaces in the direction transverse to the magnetic field. A one-dimensional problem of an electrode sheath is formulated in which all of the quantities depend only on the coordinate orthogonal to the electrode surface. Viscous plasma heating, plasma cooling via heat conduction, and other kinetic effects are taken into consideration. Account is also taken of the effect of plasma acceleration and of the related current that is transverse to the electrode surfaces and, due to the Hall effect, carries the magnetic flux away from the cathode and toward the anode. Solving the one-dimensional problem with a constant electric current and constant magnetic field shows that, in a sheath that forms near the cathode, the solution becomes self-similar, the plasma mass grows linearly, and the electron magnetization parameter remains unchanged. It is found that the anode sheath cannot be described in the magnetohydrodynamic approximation, according to which the plasma density in the sheath rapidly vanishes, while the current through the sheath remains constant. This difficulty can be overcome by incorporating some of the nonhydrodynamic effects (primarily, electron dispersion), thereby making the problem physically correct. Solving the problem numerically shows that a decrease in the plasma density in the anode sheath due to the Hall effect gives rise to additional significant plasma acceleration.