Table of contents

The diffraction of electromagnetic waves on a cylindrical plasma is numerically computed. The calculations are made using the geometrical optics approximation and then the wave equation (exact solution). The electric field vector of the incident wave is taken as parallel to the axis of the cylinder. The calculation is carried out for a constant electron density N and for a Gaussian density distribution [N = N₀ exp (-a²r²)].

Propagation of magnetohydrodynamic waves in a magneto-plasma-filled waveguide is described by a model formulated on the basis of Maxwell's equations and the quasi-one-fluid equations. The plasma is non-viscous and fully ionized. In this approximate treatment, effects of pressure; current inertia; resistivity; diffusion due to partial pressure gradients and different ion and electron temperatures; displacement current; and Hall effect on the propagation of the lowest mode, uncoupled, Transverse Magnetic (TM), and Transverse Electric (TE) waves are discussed. Results include the appearance of two additional acoustic waves and accentuate results previously obtained by consideration of non-vanishing plasma pressure.

Experiments are described in which energetic molecular hydrogen ions were injected into a magnetic mirror trap with a spatially-periodic modulation of the central field. The resonant non-adiabatic trapping of a well-collimated beam resulted in a mean lifetime for injected particles corresponding to about 40 transits of the system. The lifetime was reduced when the angular divergence of the beam was increased. The experimental results show satisfactory agreement with numerical calculations of particle orbits in a `square wave' model of the non-adiabatic field. The protons formed inside the trap by dissociation on background gas had a non-adiabatic loss time corresponding to about 700 transits.

Trapped ion densities up to 10⁸ cm^-3 were obtained. No flute instabilities were observed, probably because of the stabilizing effect of cold plasma, which was present with a density comparable with the fast ion density.

It is shown theoretically that the trapped densities could be increased about 25-fold using a stochastic, rather than a resonant, arrangement of the trap.

Low-frequency longitudinal oscillations are studied in a weakly ionized, collision-dominated plasma in the presence of an external electric field. The relaxation process of a perturbed velocity distribution function is examined and a new expression for the conductivity is calculated.

In this paper we investigate the non-linear generation of high-frequency longitudinal waves in cold beam-plasma systems in the presence of an external magnetic field. Much emphasis has been given to the implications of the resonant conditions [equations (1)], for three special systems, i.e. plasma, beam and beam-plasma.

A new class of closed line, ∮(dl/B)-stable, plasma containment systems which do not require floating conductors is discussed. The properties of one such system are described in detail.

Detailed knowledge of fast neutron interactions is important for conceptual designs of blankets for thermonuclear reactors. A Monte Carlo calculation, based on a collision density approach, was made of the energy and spatial flux distribution in water from a 14.7 MeV neutron fusion source. The results are compared with an earlier moments method solution of the Boltzmann equation. A concurrent experimental study by a threshold detector technique proved relatively ineffective at determining accurate flux spectra near the neutron source because of the dominant influence of uncollided flux. Reasonable agreement between experiment and theory was found, however, in a comparison of measured activation integrals and ones computed from both the Monte Carlo and the moments method results.

Macrons are defined as macroscopic particles (e.g. dust particles). If methods of acceleration can be discovered for producing energetic macrons then a new field of macron physics will emerge. A few possibilities are briefly mentioned, in particular the possibility of controlled thermonuclear power. Some speculative ideas on macron-beam interactions, such as rocket propulsion in a neutral beam and ramrod acceleration in a charged beam, are discussed as possible means for attaining energies higher than have been previously achieved.

A plasma of argon seeded with caesium is studied at atmospheric pressure. The effect of electron heating appears on the conductivity curve obtained by measurement of the electric field with a double probe. The seeding ratio is varied from 1.2 × 10^-4 to 6.2 × 10^-3 and the current density from 0 to 45 A/m². Theoretical analysis accounting for elastic and inelastic energy losses of the electrons and of ionization both argon and caesium is in good agreement with the experiment. A step in the conductivity curve corresponding to full ionization of the caesium which appears experimentally at high current density is well described by the theory.

The purpose of this work is to examine the stability of a cylindrical layer of relativistic particles in a geometrical configuration that approximates the Astron machine. The model is that of a long thin cylindrical shell of relativistic electrons that gyrate in an axial magnetic field and are enclosed in cylindrical conducting walls. It is shown that a number of the lower azimuthal (`negative-mass') modes can be rendered stable even in the absence of any energy spread by the proximity of a highly conductive outer wall. This stabilization is a property of the cylindrical geometry, and is in marked contrast to the results for a toroidal tank geometry such as those used in particle accelerators. A calculation of the instability growth rates in the presence of the Astron resistor structure is also presented.

Longitudinal plasma oscillations are investigated in the presence of a beam of electrons possessing a large velocity component V_⊥0 perpendicular to the external magnetic field B₀. The angle between the wave vector k and the external magnetic field is taken equal to π/2. If the wave frequency ω is large compared with the gyration frequency of the beam electrons and the wavelength is small compared with their gyration radius, the instability appears under the resonance condition ω = kv_⊥0.

With ω ≪ kv_⊥0 in a rather dense plasma, the Langmuir frequency Ω_p exceeds considerably the gyration frequency ω_c, and the oscillations are excited with frequencies close to the half-integral harmonics of the gyration frequency. In the case when the wavelength is of the order of the beam electron gyration radius, it is oscillations with frequencies near the hybrid one, √(Ω_p² + ω_c²) that appear unstable (herein, √(Ω_p² + ω_c²) = Lω_c, L = 2, 3,...).