Detailed measurements of the trapped magnetic fields and currents in plasma structures generated by conical theta-pinches are reported. Studies of these structures interacting with a magnetic barrier, and with each other in a collision at the centre of a magnetic mirror, are reported. The magnetic well formed by the collision has been studied by simultaneous use of several diagnostic techniques. The measurements are in agreement with a force-free, collinear magnetic field configuration (Wells 1972). Arguments relating superposability and collinearity of flow fields to these observations are given.

The instability of the ordinary electromagnetic mode propagating perpendicular to an external magnetic field is investigated for two ion beams with anisotropic temperatures, counter-streaming along the magnetic field. A necessary and sufficient condition for instability is derived. The growth rate is calculated, and found to be typically several times the ion cyclotron frequency Ωi, although in extreme cases γmax may be as large as (Mi/me)½Ωi.

Resonant interaction between three ordinary modes, modified by electrons streaming parallel or antiparallel to the static magnetic field of a homogeneous plasma, is investigated. The modes propagate perpendicular to the magnetic field. If the unperturbed current density is zero, the scattering matrix for three-wave resonant interaction depends only on the cube of the electron drift velocity. If two electron beams of equal density are counter-streaming, the scattering matrix vanishes completely. If the unperturbed current density is non-zero, the matrix depends on the linear and cubic terms in the electron drift velocity. In the present investigation, the Hamiltonian approach, which is microscopic in nature, has been used, and therefore the results are valid for arbitrary ratios of Larmor radius to wavelength.

We investigate electrostatic surface-wave damping in strongly inhomogeneous magneto-active plasma with collisions. We demonstrate that such damping occurs at wave frequencies close to the natural (hybrid) frequencies of the plasma oscillations. We obtain dispersion equations and expressions for the damping coefficients of surface waves propagating along (i) the interface of semi-infinite plasmas, (ii) a plane plasma layer, and (iii) a vacuum layer in the plasma. We also study the linear transformation of surface waves into longitudinal oscillations (concentrated in the transition layer and directed along the gradient of plasma density) caused by the initial perturbation.

The reconnexion rate of magnetic fields is crucial in understanding the fields found in turbulent flows in the solar photosphere and in the galaxy, and in flare phenomena. This paper examines the behaviour of magnetic fields in the neighbourhood of an X-type neutral point. The treatment is kinematical, specifying the velocity field v and constructing solutions to the hydromagnetic equation for B. The calculations demonstrate that the reconnexion rate is controlled by the diffusion in the near neighbourhood of the neutral point, and is not arbitrarily large, as has been suggested by similarity solutions of the complete field and fluid equations for vanishing diffusion

A technique involving the use of a trial function containing several adjustable parameters has been developed for the purpose of deducing the electrical conductivity from measurements on the electric arc. It is used to re-analyze experiments in argon, xenon and nitrogen. Some improvement in agreement between theory and experiment is noted.

At plasma densities lower than about 1018 cm-3, strictly speaking, the LTE model cannot be used when the electron temperature is calculated from measured spectral line intensity ratios. In this work a number of nitrogen spectral lines were studied at an electron density of about 1016 cm-3, and the results are discussed with reference to the LTE and semi-coronal models. A method is suggested for analyzing line intensity ratio data from plasmas in the semi-coronal regime.

Dispersion curves are plotted for the extraordinary branch of the electron- and ion-cyclotron harmonic waves propagating perpendicularly to the static magnetic field in a non-relativistic, hot Maxwellian plasma, without invoking the electrostatic approximation. It is found that, except in the vicinity of the cyclotron harmonics and the hybrid resonances, either the cold-plasma or the electrostatic approximation are accurate representations of the exact solution. The hybrid resonances of the cold-plasma model become monotonically shrinking regions of low group velocity as the temperature is increased, till all discernible evidence of these resonances disappears as the parameters corresponding to the thermonuclear plasmas are approached.

Thermodynamic bounds on the magnetic fluctuation energy in unstable anisotropic plasmas are obtained. The spatial variation in equilibrium and perturbed quantities is assumed to be exclusively in the z direction, which coincides with the direction of a uniform external magnetic field B0êz. In addition, the positive ions are assumed to form a fixed (mi→ ∞) background providing overall charge neutrality, and only the electron dynamics are included in the analysis. For this configuration it has recently been shown that the non-linear Vlasov–Maxwell equations support two independent energy constants for arbitrary-amplitude electromagnetic disturbances propagating parallel to B0 êz. In this paper, Fowler's method for calculating thermodynamic bounds on the field energy in unstable plasmas is generalized to incorporate two energy constraints (in addition to entropy and number conservation). An upper bound on the magnetic fluctuation energy is obtained for arbitrary initial distribution function fe0 = fe(z, v, 0), and the results are applied to unstable (i) bi-Maxwellian and (ii) loss-cone distributions. Depending on the parameter regime, it is found that the bounds obtained by enforcing two energy constraints can be an order-of-magnitude lower than the bounds obtained by enforcing a single (total) energy constraint. The theoretical bounds are compa red with the maximum change in field energy measured in computer simulation experiments for the case where fe0 is bi-Maxwellian. For sufficiently large initial anisotropy, it is found that the bound obtained with two energy constraints is less than 1·5 times the measured change in field energy.

Allis modes are large-ampliturde, undamped electrostatic plasma waves, in which the trapped electron distribution is the analytic continuation of the untrapped distribution. Allis modes can be pulse-like, as well as periodic. As the amplitude of the periodic solutions increases, the frequency decrsases and the wavelength increases, leading finally to solitary pulse solutions as a limiting case, reached when an appreciable number of electrons are trapped by the wave. These pluse-like solutions imply a maximum amplitude to Allis modes, and a maximum d.c. current they can drive. A simple approximate expression gives the non-linear properties of Allis modes in terms of the linear properties and the maximum amplitude.

It is well known that the properties of stable quiescent plasma may be calculated by a method known as the ‘superposition of dressed particles’. In this paper an analogous superposition principle is constructed for turbulent plasmas. This shows that the turbulent fluctuations may suppress the growth of the instabilities that give rise to them. The fluctuation spectrum, diffusion coefficient and dielectric constant of turbulent plasma are calculated for the guiding centre model. The relationship of this theory to that of Dupree and Weinstock is discussed.