It is shown that both lower hybrid and modified electron acoustic instabilities can be excited in a hot anti-loss-cone plasma co-existing with a rarefied cold plasma, provided the anti-loss-cone factor, ρ, exceeds a value Tm/Tt, where Tm and Tt are the parallel temperatures of missing and trapped electrons respectively. These instabilities are excited in a bounded range of wavenumbers and the growth rates are enhanced with the increase of cold plasma density. For

Tm/Tt < ρ > (Tm/Tt)½

both the instabilities are of resonant type whereas for ρ > (Tm/Tt)½ both may be converted into non-resonant types. These instabilities are expected to give rise to the heating of protons as well as electrons in the magnetosphere beyond the plasmapause.

A new approach to the problem of the radiation emitted from a localized external current source embedded in a magnetoplasma is described. It is argued that the calculation of the fields in the radiation zone can be substantially simplified by adopting at the outset a suitable parametrization of the dispersion surface. We illustrate the approach by calculating the far fields using the full expression for the dielectric tensor of a warm magnetized electron gas. In this case one can take the angle of rotation about the external magnetic field and the square of the refractive index as the curvilinear co-ordinates of the dispersion surface. The form of the surfaces of constant phase and the amplitudes of the emitted waves are described for each topologically different region of parameter space and their structures are related to the shapes of the refractive index surfaces. Attention is also drawn to the existence of locally cylindrical waves that can produce beams which are highly collimated in the direction of the external magnetic field.

A formalism is described which permits calculation of the low frequency response of a resistive plasma with non-circular cross-section in magnetohydrodynamic equilibrium to an externally imposed current field in the direction of the ignorable co-ordinate. This formalism is limited to slow variations on the resistive penetration or ‘skin’ time-scale and eliminates rapid motions at the hydrodynamic rate. It is useful for calculating the effectiveness of low frequency Ohmic heating and for the study of feedback stabilization. It also determines stability criteria and gives estimates of growth rates. The presence of a hyperbolic axis in the Doublet configuration makes the incorporation of a finite resistivity in the treatment important.

Ion-cyclotron waves are excited by cesium and potassium ion beams in cesium and potassium Q-machine plasmas. The ion beams are injected along the magnetic field with care to avoid beam transverse velocities. The observed ion-cyclotron mode frequencies are below those driven by electron currents. These resonant instabilities are convective in character with small spatial growth rates ki/kr ≃ 0.05. Plasma ion heating is observed and is consistent with a model in which mode amplitudes are saturated by diffusion effects.

Ion-cyclotron waves are excited by a cesium ion beam in a cesium Q-machine plasma with drifting plasma electrons. These interactions differ significantly from those in the case of drifting ions in that the drifting electrons play an active role in the instability mechanism. The observed mode frequencies are slightly below those of the electron current driven modes. These waves can be convectively or absolutely unstable, depending on the ion beam velocity. For low beam velocities the instabifities are convective in character with large spatial growth rates ki/kr ∼ 0.2. For larger beam velocities the instabilities are absolute in character with temporal growth rates 0.04. The absolute instabilities are similar to two-stream instabilities. Plasma ion heating is observed and is consistent with a model in which mode amplitudes are saturated by diffusion effects.

Thomson scattering was used to determine space- and time-resolved electron velocity distribution components parallel and transverse to the magnetic field direction in a Penning-type reflex discharge in hydrogen. Electron densities were of the order 1013 cm-3, and temperatures about 3eV. For magnetic field strengths less than about 200 G, Maxwellian distributions were obtained over an energy range six times the thermal energy. Temperatures were in excellent agreement with Langmuir probe data. However, for fields of about 4500 G chaotic plasma potentials were observed with the Langmuir probe. In this regime, in which the plasma was unstable, Thomson scattering showed electron velocity distributions having central temperatures of about 2eV and wing temperatures of 15–20 eV. The experiment design employed led to extremely low stray light levels permitting clean measurements at the laser wavelength and detection of scattered signals as faint as two photons.

The quasi-static lower hybrid eigenmodes of a plasma column in a cylindrical waveguide are determined, and their linear excitation by a small density electron beam is discussed for the cases of a hot electron beam as well as for a cold electron beam. It is shown that under certain conditions, finite geometry effects introduce important quantitative and qualitative differences with respect to the results obtained in an infinite geometry.

The dispersion relations for the quasi-static lower hybrid surface waves are derived. Conditions for their existence and their linear excitation by a small density electron beam are discussed. Instabilities appearing in low-frequency surface waves are also discussed.

Following Akhmanov's approach, self-focusing of a laser pulse in a transient plasma has been studied. The beamwidth parameter and hence the laser intensity and the frequency shift (time derivative of the phase) have been evaluated as a function of time and the distance of propagation. It is seen that the time dependence of the axial intensity changes appreciably as the pulse propagates. The present investigation is restricted to a pulse whose incident intensity has Gaussian radial dependence.

The parametric decay of an intense electromagnetic (pump) wave into a back-scattered electromagnetic wave and an electron plasma wave is considered. The dispersion relation for a homogeneous magnetized plasma in the presence of the pump wave is developed in the cold-plasma approximation with the pump frequency large compared to the cyclotron and plasma frequencies. Formulae are derived for the growth rate γ and threshold power PT associated with the instability. The effects of the magnitude and direction of the static magnetic field on γ and PT are studied numerically.