On the theory of Cherenkov emission from a short laser pulse in a magnetized plasma

Cherenkov emission from a short laser pulse propagating in an underdense plasma along a constant magnetic field is considered. The spectral, angular, energy, and spatiotemporal parameters of the emitted radiation are investigated. It is shown that the spectral content of the radiation and its directionality depend sensitively on the plasma and laser-pulse parameters. For instance, the most intense backward radiation at the upper hybrid frequency is generated by a tightly focused laser pulse.     

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.     

Emission of low-frequency electromagnetic waves by a short laser pulse propagating in a plasma with density fluctuations

It is shown that a short laser pulse propagating in a plasma with electron density fluctuations can emit electromagnetic waves with frequencies much lower than the laser carrier frequency. Emissions with frequencies close to the plasma frequency and the doubled plasma frequency in a nonisothermal plasma, as well as emission generated in a turbulent plasma, are examined. The effects in question are related to the transformation of the laser pulse wakefield into electromagnetic radiation by electron density fluctuations. The phenomenon under study opens new possibilities for diagnostics of both plasma fields excited by laser pulses and electron density fluctuations in a plasma.     

Weibel instability in the field of a short laser pulse

The growth rate of Weibel instability in a plasma interacting with a high-frequency pulse with a duration less or comparable with the electron mean free time is determined. The growth rate is shown to decrease with decreasing pulse duration. It is found that instability can develop after the short pulse is switched off and the generated magnetic field no longer affects electron motion in the high-frequency field.     

Decay instability of a lower hybrid wave

A study is made of the decay instability of a lower hybrid wave with a finite wave vector (k ₀≠0) and a large amplitude such that the oscillatory velocity of the electrons with respect to the ions cannot be neglected. It is shown that, depending on the angle between the propagation direction of the lower hybrid wave and the external magnetic field and the angle through which the wave is scattered, the decay instability is primarily governed either by the oscillatory electron motion with respect to the ions or by the nonlinear response of the plasma to the lower hybrid wave propagating in it. The role of the nonlinear frequency shift in the saturation of the lower hybrid decay instability is clarified.     

Thomson scattering in a plasma created by a short intense laser pulse

Thomson scattering spectra from a plasma created through ionization of a gas consisting of multielectron atoms by a laser pulse with an intensity of about 10¹⁶ W/cm² or higher and with a duration τ_imp≤100 fs are studied theoretically with allowance for electron groups with different temperatures.     

Excitation of Langmuir oscillations by a laser pulse in a semi-infinite dense plasma

A study is made of the nonlinear mechanism for the excitation of Langmuir waves in a dense plasma by an intense laser pulse with the frequency ω = ω_p/2 (where ω_p is the electron plasma frequency).     

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.     

Excitation of magnetic fields by a circularly polarized laser pulse in a plasma channel

The excitation of quasistatic magnetic fields by a circularly polarized laser pulse in a plasma channel is considered. It is shown that, to second order in the amplitude of the electric field of the laser pulse, circular rotation of the plane of polarization of the laser radiation in a radially nonuniform plasma gives rise to a nonlinear azimuthal current and leads to the excitation of the radial and axial components of the magnetic field. The dependence of the magnetic field distribution over the plasma channel on the spatial dimensions of the pulse and on the channel width is investigated for a moderate-power laser pulse. The structure of the magnetic fields excited by a relativistic laser pulse in a wide plasma channel is analyzed.     

Breaking of a wake wave excited by a narrow laser pulse in a low-density plasma

The spatial structure of a wake wave excited in a low-density plasma by a laser pulse with a small focal spot radius is studied both analytically and numerically. Numerical study shows that, in a small-amplitude laser field, a wake wave breaks after the formation of an off-axis density maximum, which grows in height away from the pulse to become infinitely high after several periods. Analytical and numerical calculations show that the singularity in the density arises from the intersection of the trajectories of neighboring particles. Numerical simulations demonstrate that, as the laser field amplitude increases, the breaking point of the wake wave rapidly approaches the pulse trailing edge. For weakly nonlinear conditions, an analytic dependence of the coordinate of the breaking point on the amplitude and transverse size of the laser pulse is obtained.     

Excitation of surface waves at a plasma boundary by a short laser pulse

The excitation of surface waves by a laser pulse as it crosses a vacuum-plasma interface is considered. Surface waves are excited by a vortex electric current that is generated at the plasma boundary by the ponderomotive force of the pulse. The question is considered of how the duration and transverse dimensions of the pulse affect the spatiotemporal distribution and the spectral and energy parameters of the excited surface waves.     

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.     

Electron acceleration by Langmuir waves excited by a laser pulse in a semi-infinite plasma

Results are presented from a theoretical investigation of the acceleration of test electrons by a Langmuir wave excited by a short laser pulse at half the electron plasma frequency. Such a pulse penetrates into the plasma over a distance equal to the skin depth and efficiently excites Langmuir waves in the resonant interaction at the second harmonic of the laser frequency. It is shown that the beam of electrons accelerated by these waves is modulated into a train of electron bunches, but because of the initial thermal spread of the accelerated electrons, the bunches widen and begin to overlap, with the result that, at large distances, the electron beam becomes unmodulated.     

Generation of terahertz radiation in the reflection of a laser pulse from a dense plasma

The generation of low-frequency (terahertz) electromagnetic radiation in the reflection of a laser pulse from the boundary of a dense plasma is considered. Low-frequency wave electromagnetic fields in vacuum are excited by a vortex electric current that is induced at the plasma boundary by the ponderomotive force of the laser pulse. The spectral, angular, and energy parameters of the low-frequency radiation, as well as the spatiotemporal structure of the emitted waves, are investigated. It is shown that for typical parameters of present-day laser plasma experiments, the power of terahertz radiation can amount to tens of megawatts.     

Stochastic electron acceleration in plasma waves driven by a high-power subpicosecond laser pulse

The mechanism of stochastic electron acceleration and heating by a picosecond laser pulse in underdense plasma is studied using particle-in-cell simulations and theoretical models. The formation of wide electron energy spectra in the simultaneously acting laser and plasma fields is analyzed. It is shown that electron scattering by turbulent plasma fluctuations excited through stimulated forward Raman scattering plays a governing role in the formation of high-energy tails in the electron distribution function.     

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.     

Efficiency of ion acceleration by a relativistically strong laser pulse in an underdense plasma

A particle-in-cell simulation is used to investigate ion acceleration by a femtosecond laser pulse propagating in an underdense plasma slab. In plasma slabs with different thicknesses, the ions are found to be accelerated by different mechanisms. It is shown that, for laser pulse intensities in the range (5–10)×10¹⁹ W/cm², the ions are accelerated near the plasma-vacuum interface. __________ Translated from Fizika Plazmy, Vol. 27, No. 3, 2001, pp. 225–234. Original Russian Text Copyright ￠ 2001 by Kuznetsov, Esirkepov, Kamenets, Bulanov.     

Generation of terahertz radiation from a low-density plasma slab irradiated by a laser pulse

The generation of terahertz electromagnetic radiation when a laser pulse propagates through a low-density plasma slab is considered. It is shown that terahertz waves are excited because of the growth of a weakly damped, antisymmetric leaking mode of the plasma slab. The spectral, angular, and energy parameters of the terahertz radiation are investigated, as well as the spatiotemporal structure of the emitted waves. It is demonstrated that terahertz electromagnetic wave fields are generated most efficiently when the pulse length is comparable to the slab thickness.     

Radial structure of the wakefield excited during the self-modulation of a laser pulse in a plasma

A study is made of the structure of the wakefield excited in the linear stage of the self-modulation of a high-power laser pulse in a homogeneous underdense plasma. It is shown that the fronts of the wake wave are curved and the profile of the wakefield amplitude differs strongly from the intensity profile of the laser pulse. The diffraction effects are found to play a key role in the formation of the transverse profile of the wakefield.