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.

The magnetic field and flow with an X-type neutral point or stagnation point are studied numerically for the steady state of incompressible, finitely conducting, viscous fluid in two dimensions. There appear two transition layers connecting smoothly the regions on either side, each of which contains almost uniform magnetic field and flow. The electric currents are concentrated in the vicinity of the neutral point and along the transition layers. The magnetic field is regarded as almost frozen in the fluid in other current-free regions, even in the case of moderate conductivities. The current-core over the neutral point is accompanied by a remarkable shear of currents, which may contribute to reducing the local electrical conductivity effectively. Thus the re-connexion of magnetic lines of force may be possible even in very highly conducting fluids. It is shown that the re-connexion is not essentially influenced by dissipations due to finite electrical conductivity or viscosity, but definitely by external conditions such as the applied electric field in the magnetic field and flow.

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.

A differential equation in wavenumber space is used to find the electric field excited by an external source in a weakly non-uniform, low-β, neutral magneto- plasma slab (with B perpendicular to ∇n). The analysis is general enough to allow one to judge the accuracy of previously used long-wavelength methods. Electrostatic waves which propagate across the magnetic field parallel to the density gradient are considered, and the impedance of a grid-plasma system is determined. The calculation is specialized to the case of a low density plasma with applied frequencies near the upper hybrid.

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.

Propagation characteristics of two magnetosonic waves, the fast and slow modes, in layered plasmas with different β values are studied, where β is the ratio of plasma pressure to magnetic pressure. In the first part we consider the efficiency of wave penetration from one region to another with different β ratios, β1 and β2. In particular, the condition for the total reflexion, amplitude and phase of the reflexion and transmission coefficients at the interface are obtained for both modes. The results indicate that the range of deviation of the ratio β2/β1 from unity is very small for penetration of the slow mode, while the ratio for the fast mode covers a wide range. In the second part, the fast and slow normal modes of magnetosonic waves in layered plasmas are discussed and their phase and group velocities, and the spatial damping rate due to partial leakage of wave energy are compared between two modes. From these, it is concluded that the presence of the slow magnetosonic waves is restricted to within the high-β plasma region. Finally, application of these to the earth's magnetosphere is given qualitatively.

The problem of propagation of finite-amplitude electromagnetic waves in a plasma containing random irregularities is studied. Using a recently developed perturbation technique, a general equation for finite amplitude coherent waves is derived. Included in this equation are both the effects of quasi-harmonic nonlinear heating of electrons and random scattering by irregularities. The equation is solved in general by the equivalent linearization procedure. The amplitude of the coherent wave is found to be attenuated by collision and scattering. Both attenuation are affected by the nonlinear heating of the electrons. Curves showing the results for a specific example will be presented.

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.