The gravitational instability of an infinite homogeneous, finitely conducting, rotating, collisionless, anisotropic-pressure plasma in the presence of a uniform magnetic field with finite-ion-Larmor-radius (FLR) corrections and generalized polytropic laws is investigated. The polytropic laws are considered for the pressure components in directions parallel and perpendicular to the magnetic field. The method of normal-mode analysis is applied to derive the dispersion relation. Wave propagation is considered for both parallel and perpendicular axes of rotation. Longitudinal and transverse modes of propagation are discussed separately. The effects of rotation, finite electrical resistivity, FLR corrections and polytropic indices on the gravitational, firehose and mirror instabilities are discussed. The stability of the system is discussed by applying the Routh–Hurwitz criterion. Extensive numerical treatment of the dispersion relation leads to several interesting results. For the transverse mode of propagation with the axis of rotation parallel to the magnetic field, it is observed that rotation stabilizes the system by decreasing the critical Jeans wavenumber. It is also seen that the region of instability and the value of the critical Jeans wavenumber are larger for the Chew–Goldberger–Low (CGL) set of equations in comparison with the magnetohydrodynamic (MHD) set of equations. It is found that the effect of FLR corrections is significant only in the low-wavelength range, and produces a stabilizing influence. For the transverse mode of propagation with the axis of rotation parallel to the magnetic field, the finite electrical resistivity removes the polytropic index [nu] from the condition for instability. The inclusion of rotation alone or FLR corrections alone or both together does not affect the condition for mirror instability. The growth rate of the mirror instability is modified owing to uniform rotation or FLR corrections or both together. We note that the condition of mirror instability depends upon the polytropic indices. We also note that neither the mirror instability nor the firehose instability can be observed for the isotropic MHD set of equations.

Shock waves in plasmas with strongly anisotropic viscosity and thermal conductivity are considered. The analysis is restricted to the case where the plasma beta is less than unity. The set of two equations that governs propagation of small-amplitude MHD waves at small angles with respect to the unperturbed magnetic field in such plasmas is derived. A qualitative analysis of this set of equations is carried out. It is shown that the shock structure is described by a solution that is a separatrix connecting two stationary points: a stable node and a saddle. This solution describes the structure of a fast quasiparallel shock wave, and it only exists when the ratio of the magnetic field component, perpendicular to the direction of shock-wave propagation after and before the shock is smaller than a critical value. This critical value is a function of the plasma beta. The structures of shock waves are calculated numerically for different values of the shock amplitude and the ratio of the coefficients of viscosity and thermal conductivity.

In this paper, a set of two-dimensional simulations for resistive magneto-hydrodynamical equations are performed to investigate the interaction between a solar-wind filament and the magnetosphere when the filament is obliquely oriented with respect to the direction of the magnetospheric field. Detailed pictures for the interaction are given. For typical parameters near the magnetopause, a filament with a sufficiently large excess flow velocity will penetrate into the magnetosphere, and will then be repelled back towards the magnetopause by the highly compressed and bent magnetospheric field. Finally, the filament will be smeared along the magnetospheric field near the magnetopause. When the angle is small, the filament will penetrate deeply into the magnetosphere before it is repelled back. Therefore there is a maximum depth a penetrated filament may reach into the magnetosphere. The effect of spontaneous reconnections behind a penetrating filament on the penetration appears to be negligible.

The effect of neutral-gas friction on Alfvén surface waves propagating along an infinitely conducting viscous plasma–vacuum interface has been investigated. A dispersion relation is obtained for such waves. For different values of the neutral-gas friction parameter S=νc/ω (where νc is the collisional frequency between two components of the composite plasma), the variations of the real and imaginary parts kr and ki of the wavenumber k with the viscosity parameter vp= μlω/ρ01v2A1 (where μl and ρ01 are the coefficient of viscosity and the density of plasma media 1) are shown graphically. It is concluded that a three-mode structure of Alfvén surface waves results flowing to neutral-gas friction. It is suggested that our results are useful for both laboratory and astrophysical plasmas (e.g. photospheres, chromospheres and cool interstellar clouds).

The recent high core gains of 29% in laser fusion experiments at the LLE Rochester are evaluated and compared with related earlier measurements where surprisingly the self-similarity model for volume compression provides a common description. This is a proof that the isentropic conditions of stagnation-free compression were mostly fulfilled at the optimized experimental gains, in contrast to highly entropy-producing shock and central spark conditions. Some projections are given of how these results may be generalized to volume ignition for the parameters of the NIF (National Ignition Facility). The proof of stagnation-free volume compression for the best laser fusion gains indicates the advantages of volume ignition, which not only is ‘robust’ and simply follows the natural adiabatic compression, but also is much less sensitive to instabilities and mixing. However, its essential advantage is that it is free from symmetry problems – in contrast to spark ignition, with its spherical detonation front.

The dynamics of a magnetic field in a plasma with dominant Hall effect is examined. The evolution of B in the problem is under the essential influence of the fluctuations in plasma density generated by ∇B2. Solutions of two self-consistent EMHD problems are obtained. It turns out to be possible to obtain analytical results with the use of small parameters. The phenomena described here include self-similar nonlinear waves and the escape of a small-amplitude precursor from a convective wave.

This paper reports progress in an experimental investigation, started in the Hathaway laboratory in 1994, dealing with the liberation of intermolecular bond energy from ordinary water by means of an arc discharge. Photographic evidence of fog generation and explosion during the arcing period is included. A new fog accelerator is described and a table of results of the kinetic energies of fog jets is provided. A renewable water energy cycle is outlined. The fog kinetic energy has been found to be greater than the difference between the capacitor input energy and the heat losses. Given energy conservation, the only external energy input that can account for the fog kinetic energy is solar heat from the atmosphere.

The photoabsorption cross-section of an ion immersed in a plasma is studied on the basis of the Thomas–Fermi approximation for the equilibrium electron distribution and Bloch's classical hydrodynamic model for collective motion of the electrons. The frequency-dependent cross-section scales with the nuclear charge, and depends strongly on the plasma density and temperature. An approximation of the frequency dependence is constructed with the aid of sum rules and Padé approximants.

The paper presents a paraxial theory of the relativistic cross-focusing of two coaxial Gaussian laser beams of different frequencies in a homogeneous plasma. We discuss the self-focusing of a weaker laser beam in the plasma due to the optical inhomogeneities introduced by another stronger copropagating laser beam. In the presence of the second stronger beam (Pcr21<P2<Pcr22), the plasma behaves as an oscillatory waveguide for the first, weaker, beam (P1<Pcr11) as it propagates in the plasma. When both the beams are strong (Pcr11,21<P1,2<Pcr12,22), the nonlinearities introduced by the relativistic effect are additive in nature, such that one beam can undergo oscillatory self-focusing and the other simultaneously defocusing, and vice versa. A comparison reveals that cross-focusing due to relativistic nonlinearity is possible for a wider range of powers of the laser pulses than is cross-focusing due to ponderomotive nonlinearity. Relativistic cross-focusing is important in plasma beat-wave excitation and collective laser particle accelerators.

Investigations are made of the dielectric screening and stopping power of a test charge moving in a plasma. Effects of collisions with neutral particles, if any, and the effect of an applied magnetic field with and without plasma inhomogeneity are taken into account and described.

A nonlinear equation for electrostatic electron surface waves at the boundary between a cold plasma and a dielectric is derived. Our analysis of this equation shows that the nonlinear disturbances at the plasma–dielectric interface may take the form of periodic travelling waves or standing waves with oscillating amplitudes. While the travelling waves are always periodic in space, the standing waves can be both periodic and localized.

In the heliosphere large fluctuations of the magnetic field are sometimes observed, especially at shocks (e.g. travelling interplanetary shocks, planetary bow waves, and shocks related to corotating interaction regions). The large fluctuations very often have an amplitude that reaches easily four or five times the magnitude of the quiet magnetic field. Since the plasma mostly contains a non-negligible fraction of heavy ions (e.g. helium ions or cometary water ions), these magnetic field fluctuations are described in terms of three-fluid equations. Here electrons, protons and heavy ions are considered as separate fluids interacting with themselves by electromagnetic forces. The three-fluid equations are treated in such a way that we are searching for one-dimensional stationary waves. Thus the equations are reduced to a fully nonlinear set of ordinary differential equations, which have been evaluated numerically with respect to solitary waves. Subsequently, examples of solitary waves in a electron- proton plasma loaded with 10 % 4He2+ ions are presented. For instance, an enrichment of helium ions is observed within the solitary waves.

We study the long-time behaviour of light particles, for example an electron swarm in which Coulomb interactions are unimportant, subjected to an external field and elastic collisions with an inert neutral gas. The time evolution of the velocity and position distribution function is described by a linear Boltzmann equation (LBE). The small ratio of electron to neutral masses, ε, makes the energy transfer between them very inefficient. We show that, under suitable scalings, the LBE reduces, in the limit ε→0, to a formally exact equation for the speed (energy) and position distribution of the electrons that contains mixed spatial and speed derivatives. When the system is spatially homogeneous, this equation reduces to and thus justifies, for small-enough ε, the commonly used ‘two-term’ approximation.