A model for the unsteady thermal boundary-layer development at the end wall of a shock tube, in partially ionized atmospheric argon, is proposed. Consideration is given to ionization and thermal relaxation processes. In order to obtain some insight into the influence of the relaxation processes on the structure of the boundary layer, a study of the frozen and equilibrium limits has been carried out. The transition from a near-equilibrium situation in the outer part of the boundary layer towards a frozen situation near the wall has been determined numerically. Experimental data on the electron and atom density profiles obtained from laser schlieren and absorption measurements are presented. A quantitative agreement between theory and experiment is found for a moderate degree of ionization (3 %). At a higher degree of ionization the structure of the boundary layer is dominated by the influence of radiation cooling, which has been neglected in the model.

An investigation of current production by means of a rotating magnetic field is made in an experiment in which the technique is used to generate a theta-pinch- like distribution of field and plasma. Detailed measurements are made of both the generated unidirectional azimuthal electron current and the penetration of the rotating field into the plasma. The experimental results support the theoretical prediction that a threshold value of the amplitude of the applied rotating field exists for setting the electrons into rotation.

A fast and efficient numerical procedure has been developed to solve the exact linearized stability equations of resistive magnetohydrodynamics.

Previous investigations of the stability, in particular the critical thickness for marginal stability, of an electron configuration of double-layer type are extended in order to include effects of (i) unequal plasma densities in the field-free regions, and (ii) finite values of the parameter eΔø/kTe. The results obtained are compared with the corresponding quantities in various experiments, and a striking coincidence is found.

Computer studies are performed on the temporal changes of magnetic flux surfaces and current density profiles in a tokamak (of 25 cm minor radius) undergoing current reversal. The flux on the plasma boundary is forced to vary in time so as to model a total current reversal from positive to negative in about 5 ms. A two-dimensional computer code with radial and azimuthal spatial variations has been written, as well as a simpler one-dimensional code with only radial variation. The two-dimensional code shows that the flux variation takes place in way showing the formation of magnetic islands. Both codes show that the current penetration in the plasma is much slower than the reversal time. This slow resistive penetration occurs even with an enhanced resistivity factor which increases towards the boundary and with a temperature profile which decays in time towards zero current. After maintaining a constant flat negative current for certain period, results are also obtained on the profiles during reversing back rom negative to positive current and maintaining the constant positive current.

The dyadic Green's function, relating currents and fields in transverse-k space, is determined for a homogeneous magnetoplasma, and then extended to a plane- stratified system by means of the reflexion and transmission matrices of the medium, taking into account multiple reflexions at the source and observation points. A conjugate problem is next considered, in which the propagation eigenvectors have a certain mirror symmetry with respect to those in the original problem and, by relating the scattering matrices in the two cases, a Lorentz-type reciprocity theorem is derived relating currents and fields in the original problem with the mirrored currents and their associated wave fields which characterize the conjugate problem.

It is found that convective cell diffusion leads to a kind of resistive instability for negative energy interchange modes.

The parametric excitation of Alfvén waves by two magnetosonic waves, which propagate obliquely to the static magnetic field, is analysed. The theoretical model used is the uniform, unbounded, ideally conducting and compressible one-fluid plasma, with suitable resonance conditions. Our consideration is restricted to determining the conditions under which some initially small perturbation grows, so that the magnetosonic pump wave is regarded as constant. It is found that, both in the case of the standing and the propagating pump, the growth rates of the excited waves depend not only on the pump power but also on β, and that the threshold pump intensities are proportional to β. In the case of the standing pump, the threshold pump intensity of the oscillating instability is zero at perfect matching. The parametric excitation of Alfvén waves by two magnetosonic waves, which propagate obliquely to the static magnetic field, is analysed. The theoretical model used is the uniform, unbounded, ideally conducting and compressible one-fluid plasma, with suitable resonance conditions. Our consideration is restricted to determining the conditions under which some initially small perturbation grows, so that the magnetosonic pump wave is regarded as constant. It is found that, both in the case of the standing and the propagating pump, the growth rates of the excited waves depend not only on the pump power but also on β, and that the threshold pump intensities are proportional to β. In the case of the standing pump, the threshold pump intensity of the oscillating instability is zero at perfect matching.

Single axis tokamaks as well as doublets may be unstable toward axisymmetric MHD instabilities. Such instabilities may, for the case of a single-axis tokamak, be slow when the plasma is surrounded by a relatively close fitting conducting wall, such as a vacuum chamber; the growth rate may be proportional to the resistivity of the wall material. For the case of doublets, slowly growing instabilities with growth rates proportional to the plasma resistivity exist. Such slow instabilities can be stabilized by feedback control of the currents through coils surrounding the plasma; since it is only required that the amplifiers used in the circuits respond fast compared with the growth time of the slow instabilities, this feedback stabilization is not technologically demanding. This paper describes a formalism for the stability analysis of such a system consisting of the plasma, surrounded by a conducting wall or vacuum chamber and coils with their control system.

Generation of electromagnetic surface waves by relativistic inhomogeneous particle flows is investigated for plane and cylindrical geometries. The basic excitation mechanisms are shown to be the induced anomalous Doppler effect and the hydrodynamic Čerenkov effect. The relevant maximal growth rates may differ significantly from those derived for monoenergetic beams.

For electrons in electric and magnetic fields which collide elastically with neutral atoms or molecules, a minute evolution study is made using the multiple time-scale method. In this study a set of quasi-moment equations is used which is derived from the Boltzmann equation by taking appropriate quasi-moments, i.e. velocity moments where the integration is performed only over velocity angles. In a systematic way we reveal the evolution in a transient regime where processes take place on time-scales related to the electron–atom collision frequency and electron cyclotron frequency and show how the evolution enters a regime where it is governed by a reduced transport equation. This work has relevance to the theory of evolution of gases of charged particles in general and to non-neutral plasmas and partially ionized gases in particular.

Nonlinear excitation of electrostatic and magnetostatic zero-frequency modes by finite-amplitude lower-hybrid waves is considered. It is found that modulational instabilities can give rise to enhanced plasma vortices. Dispersion relations, as well as analytical expressions for the growth rates, are obtained. The enhanced vortices may cause anomalous cross-field diffusion which can affect plasma confinement in tokamak devices when lower-hybrid waves are used for plasma heating or current drive. We found that magnetic fluctuations associated with the parametrically driven magnetostatic mode are of particular importance in tokamak plasmas.

A study is made of the equilibrium and stability of a magnetically confined collisionless plasma in the paraxial or ‘long, thin’ limit. The main field is poloidalaxisymmetric, and a stabilizing quadrupole field is superimposed.

Sufficient conditions for the stability of parallel flow of a warm N-component cylindrical plasma to electrostatic perturbations are obtained. In the unperturbed state the jth plasma component is assumed to have axial velocity Vj0(r), r being the radial co-ordinate, and the equilibrium quantities are permitted to be arbitrary functions of r consistent with the zeroth-order equations. The L2-norms of certain system variables are shown to be bounded uniformly in time. Circle theorems are obtained for the complex eigenfrequencies of any normal mode.