Formation of a steady-state shock front of a long-wavelength fast magnetosonic wave in space plasma with strong Alfvén turbulence

Plasma Physics Reports - A study is made of the propagation of a long-wavelength fast magnetosonic wave in a space plasma with a low particle density and high temperature...     

Splitting of the modes of a low-frequency magnetosonic wave in a polydisperse dusty plasma

The properties of magnetosonic waves that propagate perpendicularly to the external magnetic field in a polydisperse dusty plasma and the frequencies of which are about the dust cyclotron frequency are analyzed. A dispersion relation containing integrals of functions of the dust grain radius is derived and investigated as a function of the parameters characterizing the polydisperse properties of dust. It is found that, in a polydisperse dusty plasma, the low-frequency magnetosonic mode splits into two branches. The first, lower frequency branch has a cutoff, while the higher frequency branch has a resonance. Between the two branches, there is a forbidden frequency range within which electromagnetic waves cannot propagate perpendicular to the magnetic field. The width of the forbidden frequency range is determined as a function of the slope of the distribution function of dust grains over radii and the interval within which the dust grain radii lie.     

Solitary fast magnetosonic waves propagating obliquely to the magnetic field in cold collisionless plasma

Solutions describing solitary fast magnetosonic (FMS) waves (FMS solitons) in cold magnetized plasma are obtained by numerically solving two-fluid hydrodynamic equations. The parameter domain within which steady-state solitary waves can propagate is determined. It is established that the Mach number for rarefaction FMS solitons is always less than unity. The restriction on the propagation velocity leads to the limitation on the amplitudes of the magnetic field components of rarefaction solitons. It is shown that, as the soliton propagates in plasma, the transverse component of its magnetic field rotates and makes a complete turn around the axis along which the soliton propagates.     

Experimental investigation of the shock wave in a fast discharge with cylindrical geometry

The work is devoted to the registration and the study of the properties of cylindrical shock waves generated in the fast discharge (dI/dt ～ 10¹² A/s) inside the ceramic tube (Al₂O₃) filled by argon at pressures of 100 and 300 Pa. The shock wave appears at the inner wall of the insulator and moves to the discharge axis with a velocity of about (3?4) × 10⁶ cm/s with subsequent cumulation. The plasma behind the front is heated enough to produce radiation in the vacuum ultraviolet (VUV) region, which makes it possible to study its structure by means of a pinhole camera with a microchannel plate detector. The time resolution of the registration system was 10 ns. The analysis of VUV spectra of the plasma shows that the electron temperature behind the shock wave front is about several eV; after the moment of cumulation, its temperature increases to 20–30 eV.     

On the shock wave front speed under high-voltage electric discharge in water

The pressure wave propagation under high-voltage electric discharge in water was investigated experimentally. The shock wave front speed was determined for the considered range of parameters.     

Magnetohydrodynamics of a weakly ionized plasma: Ambipolar magnetic diffusion and shock front structure

Kinetic equations with the BGK collision integral are used to derive MHD equations for a weakly ionized plasma that are applicable over a broad range of magnetic field strengths. In strong magnetic fields, a substantial contribution to the transverse diffusion of the magnetic field comes from the ambipolar magnetic diffusion, which is associated with the motion of both the charged component and the magnetic field against the background of the neutral plasma component. The problems of the magnetic field diffusion in a weakly ionized plasma and the shock wave structure are solved.     

Generation of fast charged particles in plasma by a wave with a stochastically jumping phase

The interaction between charged plasma particles and an electromagnetic wave with a stochastic jumping phase is analyzed by numerical simulations. It is demonstrated that, in the course of interaction, the particle energy can increase by more than one order of magnitude. Optimal conditions for efficient interaction of charged plasma particles with a wave having a stochastically jumping phase are determined. According to the simulation results, substantial acceleration of charged plasma particles by a wave with a stochastically jumping phase takes place both at fixed time intervals between phase jumps and when these intervals are random. The influence of the wave parameters, such as the wave amplitude, the characteristic time interval between phase jumps, and the characteristic magnitude of these jumps, on the acceleration dynamics is analyzed.     

Formation of shock waves in a discharge plasma in the presence of a magnetic field

The effect of an external magnetic field on the dynamics of shock waves generated in an argon plasma due to both explosive processes on the cathode and expansion of the spark channel has been studied experimentally. It is shown that the expanding plasma of the cathode spot forms a shock wave and that the application of a longitudinal magnetic field decelerates the radial expansion of the cathode plasma. It is found that the intensities of some argon spectral lines increase in the presence of a magnetic field.     

Influence of kinetic effects on the structure of an ion shock wave in a plasma

The structure of a shock wave in an isotropic plasma is studied with allowance for charge separation and a self-consistent electric field.     

Formation of a boundary layer in steady-state blood flow

This paper is devoted to a study of boundary layer formation in the steady flow of blood through the human aorta. Blood is treated as an incompressible fluid. Consideration is given to a flat-top velocity profile which combines the potential flow with the boundary layer; expressions for the displacement thickness, skin-friction and pressure in the entry region are derived.     

Dissipation-free jumps for the magnetosonic branch of cold plasma motion

Dissipation-free jumps are studied in a hydrodynamic model of a cold plasma moving at about magnetosonic speed. The jumps described by the generalized Korteweg-de Vries equation, which possesses similar nonlinear and dispersion properties, are considered. In particular, jumps with emission and solitonlike jumps are considered. The assumption that our model possesses jumps of the same type as those for the generalized Korteweg-de Vries equation is justified by numerically investigating the problem of the decay of an initial discontinuity in a cold plasma. An analytic method is described that makes it possible to predict the structure of such jumps in the general case.     

Evolution of the frequency spectrum of an extraordinary wave near the upper hybrid resonance in a turbulent plasma

A study is made of the formation of the frequency spectrum of an extraordinary wave during its multiple small-angle scatterings along the path to the upper hybrid resonance, in the upper hybrid resonance region, and behind the conversion point. The formation of the spectrum is investigated both approximately (by the eikonal method) and exactly (in the limit of large-scale plasma density fluctuations responsible for small-angle scattering). It is demonstrated that these two approaches yield the same results in the common range of their applicability. It is shown that, in the vicinity of the upper hybrid resonance, the broadening of the frequency spectrum of a probing wave is proportional to its wavenumber. This circumstance and the predicted amount by which the spectrum broadens make it possible to consider small-angle scattering as one of the main effects responsible for a very large spectrum broadening observed in experiments.     

On the propagation of a wave front in viscoelastic arteries

In formulating a mathematical model of the arterial system, the one-dimensional flow approximation yields realistic pressure and flow pulses in the proximal as well as in the distal regions of a simulated arterial conduit, provided that the viscoelastic damping induced by the vessel wall is properly taken into account. Models which are based on a purely elastic formulation of the arterial wall properties are known to produce shocklike transitions in the propagating pulses which are not observed in man under physiological conditions. The viscoelastic damping characteristics are such that they are expected to reduce the tendency of shock formation in the model. In order to analyze this phenomenon, the propagation of first and second-order pressure waves is calculated with the aid of a wave front expansion, and criteria for the formation of shocks are derived. The application of the results to the human arterial system show that shock waves are not to be expected under normal conditions, while in case of a pathologically increased pressure rise at the root of the aorta, shocklike transitions may develop in the periphery. In particular, it is shown that second-order waves never lead to shock formation in finite time for the class of initial conditions and mechanical wave guides which are of interest in the mammalian circulation.     

Formation of a micropinch and generation of multiply charged ions at the front of a current-carrying plasma jet

The formation of a neck in the cathode plasma jet in the initial stage of a low-voltage vacuum spark is investigated experimentally and theoretically. X-ray bursts corresponding to an electron temperature of 150–300 eV are detected. With the use of a pinhole camera, it is found that an emitting region less than 1 mm in size is located near the cathode. The free expansion of a current-carrying cathode plasma jet with a current growing in accordance with the experimentally observed time dependence is simulated using a hydrodynamic model. It is shown that the neck forms at the front of the plasma jet due to the plasma compression by the magnetic self-field. In the constriction region, the plasma is rapidly heated and multiply charged ions are generated. The calculated spatial and temporal variations in the electron temperature and average ion charge are close to the measured dependences over a wide range of the discharge parameters.     

Measurements of the load resistance of a poloidal antenna and the phase velocity of fast magnetosonic waves during ICR plasma heating in the L-2M stellarator

The propagation and damping of waves excited by a poloidal antenna in a hydrogen plasma at the ion cyclotron resonance (ICR) frequency were investigated. The longitudinal wavenumber and damping length of waves excited in the ohmically heated plasma of the L-2M stellarator, the dependence of the damping length of fast magnetosonic waves on the magnetic field strength, and the dependence of the antenna load resistance on the plasma density were measured. It is the first time that such complex measurements were performed in experiments on ICR heating of a hydrogen plasma at the fundamental harmonic of the ion gyrofrequency in toroidal magnetic confinement systems.     

Microwave enhanced-scattering correlation diagnostics of a turbulent plasma

A study is made of the influence of large-scale plasma turbulence on the results from a diagnostic method that is based on enhanced scattering of microwaves near the upper hybrid resonance and is highly sensitive to small-scale fluctuations. The resolution in radial wavenumbers that is provided by an enhanced-scattering correlation analysis of small-scale fluctuations with allowance for multiple small-angle scatterings of the probing and scattered waves along their paths is determined. The frequency spectrum of a wave that is backscattered by the small-scale fluctuations involved in large-scale turbulent motion and undergoes multiple smallangle scatterings is analyzed.