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.     

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.     

Classical and quantum description of electron trapping during the Cherenkov beam instability in plasma

A nonlinear quantum theory of the Cherenkov instability of a nonrelativistic monoenergetic electron beam in a cold plasma is constructed. It is shown that the instability of a low-density beam is almost purely quantum in nature and results from the emission of one quantum of a plasma wave—a plasmon—by the beam electrons. The number of emitted (and absorbed) plasmons increases with beam density, so, in the limit of high-density beams, the instability becomes a classical Cherenkov beam instability in plasma. Some analytic solutions and estimates are found, detailed numerical results are obtained, and the evolution of the quantum distribution function of the beam electrons in different regimes of the beam instability is investigated.     

Axisymmetric magnetorotational instability in ideal and viscous laboratory plasmas

The original analysis of the axisymmetric magnetorotational instability (MRI) by Velikhov (Sov. Phys. JETP 9, 995 (1959)) and Chandrasekhar (Proc. Nat. Acad. Sci. 46, 253 (1960)), applied to the ideally conducting magnetized medium in the laboratory conditions and restricted to the incompressible approximation, is extended by allowing for the compressibility. Thereby, two additional driving mechanisms of MRI are revealed in addition to the standard drive due to the negative medium rotation frequency gradient (the Velikhov effect). One is due to the squared medium pressure gradient and another is a combined effect of the pressure and density gradients. For laboratory applications, the expression for the MRI boundary with all the above driving mechanisms and the stabilizing magnetoacoustic effect is derived. The effects of parallel and perpendicular viscosities on the MRI in the laboratory plasma are investigated. It is shown that, for strong viscosity, there is a family of MRI driven for the same condition as the ideal one. It is also revealed that the presence of strong viscosity leads to additional family of instabilities called the viscosity-driven MRI. Then the parallel-viscositydriven MRI looks as an overstability (oscillatory instability) possessing both the growth rate and the real part of oscillation frequency, while the perpendicular-viscosity MRI is the aperiodical instability. Published in Russian in Fizika Plazmy, 2008, Vol. 34, No. 10, pp. 908–917. The text was submitted by the authors in English.     

Asymmetric long-wavelength surface waves in magnetized plasma waveguides entirely filled with plasma

A theoretical study is made of the dispersion properties of electromagnetic surface waves with arbitrary azimuthal mode numbers and with a small axial wavenumber in cylindrical metal waveguides entirely filled with a radially inhomogeneous, cold, magnetized plasma. The frequency ranges in which the extraordinary polarized waves under analysis can exist are found, and the conditions for their resonant interaction with an ordinary bulk wave are determined. The eigenfrequency of these surface waves is investigated as a function of the plasma parameters, the axial wavenumber, and the azimuthal mode number. Simple analytic expressions are derived for the eigenfrequencies of the surface waves under study propagating in a homogeneous plasma waveguide.     

The differences in the development of Rayleigh-Taylor instability in 2D and 3D geometries

Results are presented from theoretical analysis and numerical simulations aimed to clarify specific features of Rayleigh-Taylor instability in 2D and 3D geometries. Two series of simulations, one with an isolated single-mode perturbation of the interface and the other with a random density perturbation, were performed. It is shown that the relative evolutions of integral characteristics for the first and the second series are different in 2D and 3D geometries. An attempt is made to interpret this result in the framework of the previously developed evolutionary approach based on the concept of the “critical age” of the perturbation (where, by the age is meant the product of the wavenumber and amplitude). The critical age corresponds to the destruction of the main mushroom-like structure formed during the development of Rayleigh-Taylor instability due to the onset of the secondary Kelvin-Helmholtz instability.     

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.     

Experimental study of magnetized plasma rotation in crossed fields

Rotation of magnetized plasma between two coaxial electrodes in crossed electric and magnetic fields was studied experimentally. Three regimes of plasma rotation were observed. In the first regime, the radial electric field is created by a beam?plasma discharge due to the charging of the inner axial electrode by electrons, the outer electrode being grounded. Plasma rotation in this case is accompanied by strong high-frequency current oscillations detected by a Mach probe. When a negative voltage was applied to the coaxial electrodes, the second regime was observed, in which weakly perturbed quasi-stationary plasma rotation occurred at a relatively low radial current. The third regime of plasma rotation was observed upon a spontaneous disruption of the second regime. It is characterized by high currents of ~1 kA, sheared plasma rotation, and excitation of high-frequency perturbations.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Creation of a long magnetized plasma column in a metal chamber

A method for creation of a long magnetized column of dense hydrogen plasma in a metal chamber by means of a high-current linear discharge is considered. It is the main method for the formation of preliminary plasma in the GOL-3 multimirror trap, in which a plasma column with a length of up to 12 m and diameter of 8 cm, suitable for conducting experiments on the injection of a relativistic electron beam, was obtained. Conditions for stable discharge operation in the density range of 3 × 10¹⁹–10²² m^?3 are determined, including a discharge with a uniform longitudinal plasma density profile and incomplete initial ionization of hydrogen. It is demonstrated that the system is capable of operating in a magnetic field with a variable configuration and strength of up to 6 T in the solenoidal section and up to 12 T in the end mirrors. It is shown that an important role in the development of a discharge is played by fast electrons with energies corresponding to the initial applied voltage (about 25 kV), which provide primary gas ionization. The properties of low-temperature plasma in such a discharge are discussed.