A computer investigation has been made for the problem of three coherent waves in a plasma system assuming a nonlinearly unstable situation and mutually different linear damping of the three interacting waves. The results agree satisfactorily with those of an analytic approach to the problem (Wilhelmsson 1970). In the present paper the solution near the explosion time has been further examined.

The distortion of the electron velocity distribution caused by a large amplitude Landau wave is determined analytically for the initial-value problem. The resulting stability of electrostatic perturbations impressed on the evolving plasma is studied. Narrow sidebands of the applied frequency experience consecutive growths of large magnitude during the early stages of the nonlinear wave-particle interaction. The significance of the derived results to both wave propagation experiments and triggered VLF emissions in the magnetosphere is discussed.

Nanosecond pulses are launched, and propagate on a positive column in the form of electron waves. The dispersion of the pulses is studied experimentally, and is found to be in agreement with monochromatic experiments and theory. Apart from wave attenuation, which is observed to depress signals of higher frequencies, Fourier analysis of the received pulses has revealed that the launching mechanism favours frequencies in the vicinity of 1/6ωp A full-wave theory, based on an extension of Goubau's excitation theorem, is derived, and successfully contrasted with experiment.

This paper considers electrostatic waves in a Vlasov plasma of unmagnetized ions and magnetized electrons undergoing E x B and gradient B drifts. The linear dispersion relation is solved numerically for Te & Ti. The results show that, as in the Te <Ti case, increasing electron β decreases the maximum growth rates.

The neoclassical diffusion in a tokamak is calculated for a finite-β plasma. The flux of the particles is shown to be substantially unchanged, with respect to the low-β case. The ‘equilibrium’ equation is derived. From it the magnetic surfaces can be obtained, once the external electromagnetic field and the density and temperature profiles are given. The case of magnetic surfaces with circular cross-section, in the small aspect ratio limit, is considered in detail.

We present an experimental investigation of electron cyclotron resonance plasma accelerators as a source of high-intensity, low-energy (keV) ions in which ion current and electron and ion energies are related to r.f. power and gas pressure.

A class of equilibrium configurations of Vlasov plasmas carrying a current component along an external magnetic field is presented. The present slab model contains the diamagnetic current jy, and the field-aligned current jz for arbitrary βc (= particle pressure/magnetic pressure of the applied constant field). For fixed βc and field-aligned current, our model admits a family of equilibrium solutions in which the diamagnetic currents range from zero to a maximum value. The amount of diamagnetic current flowing in a machine depends on the width of the machine, the field-aligned current and other plasma parameters. The Helmholtz free energy of the system is calculated under the constraints that the total number of particles and the field-aligned current are conserved. The least unstable equilibrium configuration in a machine is obtained by minimizing the free energy under the stated constraints among all equilibria whose plasma widths do not exceed the width of the machine.

An exact Green'ls function of the Lenard-Bernstein equation for a magnetoplasma subjected to an external d.c. electric field is obtained. The result is applied to the problem of temporal electromagnetic echoes which can be detected at any angle of observation with respect to the external magnetic field B0.

The time evolution of firehose-unstable Alfvén waves is calculated within the usual weak-turbulence scheme. In § 2 the amplitude equations are established using a third-order solution of Vlasov's equation. From these a spectrum equation is obtained by discarding four-wave correlations; in addition, we derive an equation which characterizes the truncation error ( §3). Both these equations are integrated numerically, together with the velocity-moment equations (§ 4), forward in time. The results as presented in § 5 correspond to a rapid relaxation of the plasma to equilibrium. For large wave-vectors the relaxation time, as well as the equilibrium wave energy, are in good agreement with the quasilinear treatment, and the truncation error is small. But for low wave-numbers the relaxation is much faster, and the wave energy grows higher as predicted by quasilinear theory. This is because the nonlinear particle current leads to a high effective growth rate, especially at small wave-numbers. In this region the truncation error grows appreciably, and may sometimes reach the order of magnitude of the spectrum. But the overall picture as given by quasilinear theory has been confirmed. In § 6 comparison is made with a macroscopic model of Berezin & Sagdeev (1969), where the plasma noise was simulated by ‘computer noise’. For low amplitudes both methods agree qualitatively.

The dispersion curves of mixing mode between electrostatic and electromagnetic waves propagating perpendicularly to the ambient magnetic field are computed for frequency range near the lower hybrid frequency in the case of a finite-β plasma with a Maxwellian velocity distribution. The detailed results apply to a hydrogen plasma. The result indicates that the lower hybrid frequency is neither the resonance frequency of the electromagnetic wave nor the cut-off frequency of the electrostatic wave. In a high-β plasma, the plateau of the dispersion curve disappears and the electrostatic approximation (Bernstein mode) is not valid up to the wavelength of the order of proton Larmor radius. The polarization is left-handed, and a trace of the most dominant intensity ratio of wave magnetic field energy to the electric field energy in each branch is given approximately by the cold-plasma dispersion curve.

An isotropic plasma occupies an infinite space, the upper half of which (y 0) is a dielectric. A transverse disturbance is incident obliquely on the face of the dielectric. The waves produced in each half of the space are obtained. Possible extensions are discussed. ome particular examples are considered.

It has been proposed by Smith that type III radio bursts may be produced by streams of protons with radius of the order of 7 km, which is of the same order as the characteristic lengths of the nonlinear processes which are supposed to take place in the dynamics of these bursts. In this paper, we consider a method for studying systems with finite transverse dimensions and apply it to a simple model: the scattering of a beam of plasma waves by acoustic turbulence and by the particles of the plasma.

Boundary conditions appropriate to a model with finite ion mass corrections of ideal hydromagnetic theory are reviewed. It is shown that these boundary conditions have been correctly satisfied in earlier theory for the stability of an interface between two semi-infinite regions. This theory predicts instability due to Hall current.

The influence of resistivity and Hall current on the Rayleigh-Taylor problem involving two superposed fluids of finite density in the presence of gravitational and magnetic fields normal to the fluid interface is examined. Unlike the related problem in which the magnetic field is parallel to the interface, it appears that the dispersion relation does not exhibit singular behaviour in the zero resistivity limit. The ‘potentially stable’ situation is considered throughout. The results are compared with earlier ideal and resistive theories, and an apparent anomaly regarding the existence of normal modes in such systems is resolved.