Gasdynamical equations taking radiation energy density and ponderomotive pressure into account are investigated. Conditions for these quantities to be important are stated: low absorption, reflexion at cut-off. The density ratio in a discontinuity is studied as a function of ponderomotive pressure, absorbed intensity and Mach number in the initial state. Chapman–Jouguet conditions are defined. Compressive (R type) flows and rarefaction (D type) appear. The structure of the latter is discussed including plasma effects.

An experimental, parametric investigation has been made of the disturbed ion flow field immediately downstream from conducting bodies of spherical and long cylindrical geometries in a collisionless, mesosonic plasma stream. The ion-acoustic Mach number, S, and the normalized test body potential, Φb, were varied, while the test body radii were of the order of a Debye length for all cases. In addition to standard diagnostics, the ion flux intensity, energy and direction were measured with the recently developed differential ion flux probe. These vector measurements provide direct observations of ion streamlines deflected across the wake axis at an angle proportional to sin-1 (|Φb|½/S) and show that some deflected streamlines are bunched together to form converging ion beams which can exist in the near wakes of both test body configurations. The angle of inclination of the converging ion beams depends linerarly on Φb, while the position of their intercept on the wake axis varies with S|Φb|½. The vector flux measurements also provide direct observations of secondary ion trajectory deflexions in the mid-wake region. These features exhibit parametric dependences that are in good agreement with theoretical calculations that include the effects of the test body and space charge potentials.

The Korteweg–de Vries equation which describes cylindrical or spherical converging ion-acoustic waves is solved numerically. Soliton-like structures are shown to be generated not only from compressive but also from rarefactive and mixed initial pulses. The velocity of the soliton-like structures is dependent on the initial pulse shape.

An incompressible, dissipative numerical code of the spectral type is used to follow the nonlinear evolution of a magnetohydrodynamic sheet pinch in two spatial dimensions. The evolution involves considerable turbulent activity in the electric current field, with the excited spatial scales ranging from the size of the containing volume down to the dissipation lengths of the magnetic and velocity fields. Strong current filamentation near magnetic X-points is observed, as is lsquo;jetting’, or expulsion of magnetofluid from the vicinity of the X-point parallel to the current sheet.

The stability of rippled non-neutral beams of charged particles produced under conditions in which centrifugal, space charge and magnetic forces are not balanced, is investigated. The beams are considered to be cold and assumed to partly fill a conducting pipe in the presence of an axial uniform magnetic field. The calculations hold for small ripple amplitudes and long-wavelength electrostatic perturbations (or, alternatively, thin beams). The rippled equilibrium beams considered in this work are found to support unstable, azimuthally symmetric, surface electrostatic modes. The growth rates are proportional to the relative ripple amplitude and to the effective beam plasma frequency.

In this work we study a one-dimensional model for the time-dependent behaviour caused by placing an uncharged conducting surface in contact with a uniform equilibrium plasma. Both the probe potential and plasma response are unknown a priori but are specified through a set of self-consistent model equations and boundary conditions. We investigate some numerical and analytical consequences of this model. In particular, we consider such issues as (i) the formation and expansion of a quasi-neutral region connecting the non-neutral sheath to the distant undisturbed plasma; (ii) the validity of assuming the existence of a sheath edge; and (iii) the role of both static and dynamic Bohm criteria in the theory of unsteady sheath development.

The statistical acceleration of electrons along an ambient magnetic field by large-amplitude lower-hybrid turbulence is discussed. Perturbations driven by a crossfield current and propagating nearly perpendicular to the applied magnetic field are considered. It is assumed that the instability saturates rapidly and that the fluctuating electric field is predominantly electrostatic. This work is not concerned with the detailed saturation mechanism, but rather with what happens to the electrons after the turbulence has saturated. If the turbulence is characterized by a spectrum of small parallel wavenumbers, such that the parallel phase velocity of the waves is greater than the electron thermal velocity, then the turbulence can only accelerate electrons moving with large velocities along the magnetic field. The qusai-linear diffusion equation is solved using a Green's function technique, assuming a power law spectral energy density. The time evolution of an initial Maxwellian distribution is given and the time rate of change of the mean electron energy is calculated for various cases.

The transport properties of a turbulent plasma are investigated in the vicinity of a self-similar turbulent state (SSTS). This state plays the same role of reference as the local equilibrium for a collisional plasma. The stability of the SSTS against velocity gradients is proved. Under certain well-defined conditions a plasma- dynamical regime is established, in which the initial conditions are forgotten and the macroscopic plasmadynamical quantities obey closed differential equations. The anomalous viscosity arising in this regime is investigated in detail. This quantity is time-dependent (a feature impressed by the self-similar character of the reference state). A number of additional typically turbulent terms appear in the equation of motion: they arise from interference between flow and collisions or magnetic field.

Equipotential contours for a moving test charge in isotropic Maxwellian plasma are determined numerically for a wide range of test charge speeds.

A general expression is obtained for the ponderomotive force of a HF field in a plasma. This expression is valid for both transverse and longitudinal HF fields. The conditions are discussed under which the ponderomotive force contains a term proportional to the time derivative of the HF field amplitude. This part of the ponderomotive force is termed ‘non-stationary’ ponderomotive force.

In the present paper we have studied the nonlinear interaction of an electrostatic lower-hybrid wave with a high-power Gaussian EM beam, propagating perpendicular to the static magnetic field in the ordinary mode in a collisionless hot magnetoplasma. On account of the Gaussian intensity distribution of the EM beam in a plane transverse to the direction of propagation, a d.c. component of the ponderomotive force becomes finite and leads to the modification of the background electron/ion density. Thus the electrostatic lower-hybrid wave gets coupled with the pump EM wave. This coupling can lead to the focusing of the lower-hybrid wave and if appropriate conditions are satisfied leads to Brillouin scattering.

The instability of surface wave modes in a semi infinite magnetoactive plasma with a non-homogeneous particle stream is studied. The existence of two possible mechanisms for the development of the instability: induced anomalous Doppler effect and induced Cherenkov effect is demonstrated. Related growth-rates and stability criteria are calculated.

A nonlinear dispersion relation is derived for a homogeneous, magnetized plasma by the conventional ‘ponderomotive force’ method. By using this dispersion relation, various parametric instabilities (stimulated anomalous absorptions and scatterings) are discussed. The results are compared in detail with those obtained by other authors. In the validity region of this model the results derived by previous authors can be recovered. In addition to obtaining a few instabilities which have not been published in the literature, we also find that in general (i) the ‘dipole approximation’ can give the right results for the stimulated anomalous absorption problems and (ii) the ambient magnetic field may enhance the plasma stability.

A statistical model of the collisionless or semi-collisionless equilibria of a magnetically confined plasma is presented which allows the calculation of the entropy and of the thermodynamic potentials as functionals of the collective equilibrium quantities. The entropy principle enables the identification of the magnetic equilibria which are preferentially chosen by the plasma. Stability criteria are derived by declaring unstable an equilibrium which admits in its neighbourhood an accessible equilibrium with higher entropy. The requirement of thermodynamic stability imposes considerable restrictions on the magnetic configuration, on the pressure distribution and on the velocity distribution function. New conditions for magnetic stability are derived and known results reinterpreted. The theory points towards the force-free configurations, in the case of a current carrying plasma subject to certain physical constraints, or towards the minimum-B configurations, in the general case of arbitrary ², as the most stable states from the thermodynamic point of view. The formalism is applied to identify the most promising lines to be pursued experimentally in order to achieve magnetic stability in a thermonuclear device.

The potential created by an infinitesimal alternating dipole in a Maxwellian magnetoplasma is computed numerically at the plasma and upper-hybrid resonance frequencies when the latter extends from one to three times the electron cyclotron frequency. A linear full kinetic theory is used for a homogeneous magnetoplasma for which the forced ion motion and the collisions are neglected. The integral which gives the potential is evaluated by using the least-damping- roots (LDR) approximation, i.e. by neglecting the higher-order roots of the dispersion equation for electrostatic waves. Some characteristic potential patterns of dipoles parallel and perpendicular to the magnetic field are computed and comparisons with analytical results previously published are made. The numerical and analytical patterns are similar only at the plasma frequency when the dipole is parallel to the magnetic field.

This paper presents an investigation of the excitation of an ion-acoustic wave in a collisionless hot magnetoplasma by two whistlers. On account of the interaction of the two whistlers, of frequencies ω1 and ω2, ponderomotive force at frequency △ ω(= ω1 – ω2) leads to the generation of an ion-acoustic wave. When the two whistlers have initially Gaussian intensity distributions, a d.c. component of the ponderomotive force leads to the redistribution of the background electron/ion density, and cross-focusing of the whistlers occurs. The power of the generated ion-acoustic wave, being dependent on the background ion density and powers of the whistlers, is further modified. The ion-acoustic wave power also changes drastically with the strength of the static magnetic field.

The modulation instability of small-amplitude ion-acoustic waves is investigated in three dimensions for Ti<0 (ion temperature non-zero). Relevance of results to an experiment of Watanabe is discussed. Instabilities present in this experiment are seen to be due to three-dimensional rather than thermal effects and would also appear for Ti = 0.

In this paper a theoretical description is given of the nonlinear excitation of magneto-acoustic oscillations of a magnetized plasma column by means of an oscillating axial current. These oscillations occur at the second harmonic of the axial current. A suitable choice of plasma parameters and excitation frequency leads to the usual resonant behaviour of the oscillations.

It is shown that a finite-amplitude ion-acoustic wave in a uniform magneto- plasma can enhance two-dimensional plasma vortices. The latter results from a modulational instability. The growth rates are obtained analytically.

The present paper numerically studies a nonlinear development of the Petschek mode in a sheared magnetic field where there is a field component Bz along an X line. It is found that finite-amplitude intermediate waves, adjacent to the slow shock, may eventually stand in the quasi-steady configuration; on the other hand, the fundamental characteristics of the Petschek-mode development are scarcely influenced, either qualitatively or quantitatively, by the Bz field.