Expressions for wave-induced radial transport are derived, allowing simple estimates to be obtained. The transport is enhanced owing to the presence of a poloidal magnetostatic field and in the vicinity of ion-cyclotron resonance. The direction of the wave-induced transport also depends on the wave polarization.

We consider a quasi-linear theory for the acceleration rates and propagation parameters of charged test particles in weakly turbulent electromagnetic plasmas. The similarity between two recent approaches to modelling of therandom electromagnetic field is demonstrated. It is shown that both the concept of dynamical magnetic turbulence and the concept of superposition of individual plasma modes lead to particle Fokker—Planck coefficients in which the sharp delta functions describing the resonant interaction of the particles have to be replaced by Breit—Wigner-type resonance functions, which are controlled by the dynamical turbulence decay time and the wave-damping time respectively. The resulting resonance broadening will significantly change the evaluation of cosmic-ray transport parameters.

A Gaussian laser beam propagating through a plasma heats the electrons and creates a low-density duct via ambipolar diffusion. Thermal conduction plays an important role in temperature equilibrium when the electron mean free path λm is greater than the beam radius (λm ≥ ro). For λm ≫ ro thermal conduction suppresses any non-uniformities in electron temperature, and nonlinearity is dominated by the ponderomotive force. The plasma duct traps and focuses the laser radiation above a threshold power. As the beam size shrinks, thermal conduction becomes stronger, leading to periodic self-focusing of the beam. The laser beam is also susceptible to filamentation instability. The spatial growth rate is a monotonically increasing and saturating function of the incident intensity of the beam.

Following renewed interest in the guiding-centre problem, we propose an alternative to previous approaches. It consists essentially in demonstrating the existence of a representative simple model for which the problem is rigorously solved in the Hamilton–Jacobi framework. It is shown that a perturbation method allows the extension of the model to more realistic cases. A further extension to cover both magnetic-mirror configurations and tokamaks can be achieved.

Fourier analysis is used to consider the characteristics of linear magnetosonic N waves propagating through a uniform background medium at rest, with constant uniform magnetic field В0. The disturbance is driven by an initial compressed and localized gas pressure perturbation, represented by a Dirac delta distribution. The solutions for the perturbed gas and magnetic field variables are expressed as second derivatives of appropriate wave potentials. The wave potentials split naturally into fast and slow magnetosonic components. The fast- and slow-mode wave potentials reduce to onedimensional integrals over the wave normal angle θ between the wave vector k and B0. Alternatively, the fast-mode wave potentials can be written as Abelian integrals over the slow-mode phase speed cs, whereas the slow-mode potentials reduce to Abelian integrals over the fast-mode phase speed cf. The structure of the integrals depends on the location of the observation point relative to the fast and slow magnetosonic eikonal or group velocity surfaces. Calculations of the time evolution of the magnetic field of the N wave show a family of magnetic field lines connecting the cusps of the slow magnetosonic group velocity surface, plus a further family of field lines not connected with the cusps. The wave disturbance is confined on and within the fast magnetosonic group velocity surface. The gas pressure perturbation shows singular N wave type disturbances on the fast- and slow-mode eikonal surfaces. The Green's function for the magneto-acoustic wave operator for a uniform background medium initially at rest is also obtained. Generalization of the N wave solutions for non-singular distributions of the initial gas pressure perturbation are also obtained.

Instabilities of the flute-like magnetic fluctuations in the presence of radiation cooling in a non-uniform magnetoplasma are investigated. It is shown that magnetic turbulence can cause anomalous cross-field electron energy transport. The relevance of the investigation to magnetic and inertial fusion as well as to astrophysical plasmas is pointed out.

An action principle for the Vlasov–Maxwell system in Eulerian field variables is presented. Thus the (extended) particle distribution function appears as one of the fields to be freely varied in the action. The Hamiltonian structures of the Vlasov–Maxwell equations and of the reduced systems associated with small-ampliltude perturbation calculations are easily obtained. Previous results for the linearized Vlasov–Maxwell system are generalized. We find the Hermitian structure also when the background is time-dependent, and furthermore we may now also include the case of non-Hamiltonian perturbations within the Hamiltonian-Hermitian context. The action principle for the Vlasov–Maxwell system appears to be suitable for the derivation of reduced dynamical equations by expanding the action in various small parameters.

The analouge of the Reyleigh–Taylor instability (the gravitational interchange mode) for an infinitely conducting, approximately one-dimensional plane plasma slab is examined when the gravitational acceleration g is taken to be perpendicular to the equalibrium density gradient δp0. In contrast with the ‘classical’ situation (where g is aligned with δp0), it is found for a current layer with Magnetic shear that there is no instability threshold equivalent to the ‘classical’ situation (where g is aligned with δp0), it is found for a current layer with magnetic shear that there is no instability threshold equivalent to the Suydam criterion: the mode is unstable for all values of |δp0|. In the weak shear limit the growth rate of the instability is shown to exhibit the familiar (g|δp0|/p0)img; scaling characteristic of the gravitational interchange mode.

A thermal instability is studied as an explanation of the anomalous electron density depletion observed during the electron-cyclotron resonance (ECR) heating of plasma in a tokamak device for an impurity study experiment (ISXB). Considering the fact that the background plasma has an elevated electron temperature and a localized heat source located near the ECR layer, we show that density striations having scale length 10 cm and larger can be excited via the thermal instability. The amplitude of the striations can grow by more than one e-folding during the ECR pulse period of 10 ms, which causes about 50% electron temperature elevation. A 0·1% temperature fluctuation excited by the thermal instability leads to about 50 V m-1 field fluctuation. Such a large electrostatic field can effectively cause anomalous plasma diffusion via the E ′ B drift and account for the observed 15% electron density depletion.

Long nonlinear sausage-wave propagation in a magnetic slab in an incompressible plasma is considered. The governing equation is derived with the aid of the reductive perturbation method. The solutions of this equation in the form of periodic waves of permanent shape are found numerically.

The recent interest in the electron-acoustic wave as a source of broad-band electrostatic noise in the terrestrial magnetosphere makes it interesting to ask whether it can support stationary electrostatic double layers. We investigate this problem in a fluid plasma composed of cool ions, cool electrons and a hot Boltzmann electron component – which is known to support electron-acoustic waves. Although a formal application of the reductive perturbation technique to our dynamical equations leads to an mKdV equation for electron-acoustic waves, it is found that within the present physical model the consistency conditions and required ordering of the coefficients cannot be satisfied simultaneously for reasonable parameter values. As a consequence, it is shown that the neglect of the φ(2) term in deriving the mKdV equation is unjustified under general circumstances, and furthermore that the cubic nonlinearity introduced by the mKdV equation is negligible when compared with this term. Finally, we are led to conclude that stationary, weak electron-acoustic double layers cannot exist in such a plasma.

A new model is presented for the treatment of wave propagation along an external magnetic field in a hot collisionless plasma. The analysis is based on the so-called polynomial distribution functions along the magnetic field, and takes account of enhanced fractions of high-energy particles, which are characteristic of rarefied and magnetized astrophysical plasmas, in comparison with the bi-Maxwellian distributions. These new distributions permit the derivation of general dispersion relations that are exactly valid for waves with Im (ω) > 0, and represent good approximations for those with Im (ω) > 0. Furthermore, the explicit form of the dispersion relations is shown to be valid for distribution functions of different shapes. Because of their algebraic structure, the solution of the dispersion relations can be shown to be equivalent to the determination of the roots of complex-valued polynomials. The cold plasma, the Maxwellian plasma and the so-called quasi-Maxwellian plasma appear in this formalism as asymptotic and special cases. The reliability of the model is demonstrated with the calculation of dispersion curves, growth and damping rates for several standard modes, and by comparing it with previous calculations carried out using explicit Maxwellian distributions. Finally, the tendency of the solar wind to generate ion-cyclotron waves is investigated as a first, new application.

The clarification of models of laser ablation by plasma heating is examined using a general dimensional argument and introducing a set of universal parameters. The regime of laser-plasma interaction in which collisional absorption and thermal conduction dominate is examined for spherical systems. Detailed scaling relations are derived for uninhibited and flux-limited thermal conduction. The complete set of regimes for steady spherical flow are examined, and it is found that the most important flows are thin collisional and thick local absorption.

A cylindrically symmetric, electrically driven, dissipative, energy-conserving magnetohydrodynamic equilibrium model is considered. The high-magneticfield Braginskii ion thermal conductivity perpendicular to the local magnetic field and the complete electron resistivity tensor are included in an energy equation and in Ohm's law. The expressions for the resistivity tensor and thermal conductivity depend on number density, temperature, and the poloidal and axial (z-component) magnetic field, which are functions of radius that are obtained as part of the equilibrium solution. The model has plasma-confining solutions, by which is meant solutions characterized by the separation of the plasma into two concentric regions separated by a transition region that is an internal boundary layer. The inner region is the region of confined plasma, and the outer region is the region of unconfined plasma. The inner region has average values of temperature, pressure, and axial and poloidal current densities that are orders of magnitude larger than in the outer region. The temperature, axial current density and pressure gradient vary rapidly by orders of magnitude in the transition region. The number density, thermal conductivity and Dreicer electric field have a global minimum in the transition region, while the Hall resistivity, Alfvén speed, normalized charge separation, Debye length, (ωλ)ion and the radial electric field have global maxima in the transition region. As a result of the Hall and electron-pressure-gradient effects, the transition region is an electric dipole layer in which the normalized charge separation is localized and in which the radial electric field can be large. The model has an intrinsic value of β, about 13·3%, which must be exceeded in order that a plasma-confining solution exist. The model has an intrinsic length scale that, for plasma-confining solutions, is a measure of the thickness of the boundary-layer transition region. If appropriate boundary conditions are given at R = 0 then the equilibrium is uniquely determined. If appropriate boundary conditions are given at any outer boundary R = a then the equilibrium exhibits a bifurcation into two states, one of which exhibits plasma confinement and carries a larger axial current than the other, which is almost homogeneous and cannot confine a plasma. Exact expressions for the two values of the axial current in the bifurcation are derived. If the boundary conditions are given at R = a then a solution exists if and only if the constant driving electric field exceeds a critical value. An exact expression for this critical electric field is derived. It is conjectured that the bifurcation is associated with an electric-field-driven transition in a real plasma, between states with different rotation rates, energy dissipation rates and confinement properties. Such a transition may serve as a relatively simple example of the L—H mode transition observed in tokamaks.

Nonlinear wave propagation on the surface between two superposed magnetic fluids stressed by a tangential periodic magnetic field is investigated using the method of multiple scales. A stability analysis reveals the existence of both nonresonant and resonant cases. From the solvability conditions, three types of nonlinear Schrodinger equation are obtained. The necessary and sufficient conditions for stability are obtained in each case. Formulae for the surface elevation are also obtained in both the non-resonant and the resonant cases. It is found from the numerical calculation that the tangential periodic magnetic field plays a dual role in the stability criterion, while the field frequency has a destabilizing influence.