Table of contents

A P.I.G. reflex discharge is studied experimentally and theoretically with static field B₀ < 400 gauss. The density of the plasma varying between 10¹² to 10¹⁴ particles/cm³, a weakly or strongly ionized gas could be studied. After having established the conditions of equilibrium of the discharge, a method of measuring the coefficient of perpendicular diffusion is devised and experimental results compared with theoretical. A good agreement was found.

The ion temperature of a plasma jet has been deduced by measuring the transmission of plasma through a magnetic barrier. The experimental results have been evaluated by using a theoretical model described by Gilleo.

The plasma which is produced by a hydrogenated titanium washer gun shoots into a straight vessel of 15 cm diameter and 2 m long. It propagates parallel to a magnetic field with a speed varying between 1 and 4. 10⁷ cm/sec. The magnetic guiding field at the gun and detection locations can be varied from 0 to 1000 gauss. The maximum amplitude of the magnetic barrier field, placed at the mid-plane of the vessel, may reach 14,000 gauss.

For a 1000 gauss guiding field, the observed ion temperature of the hydrogen puff turned out to be 40 ± 10 eV.

Endless lines of force confined in toroidal plasma containing geometries are subject to periodic perturbations by field errors which can produce integral, half-integral, third-integral, and quarter-integral, etc. resonant-like disturbances on the spiralling line of force. A formal analogy exists between the topology of a trace of a line of force in the co-ordinate space of a plasma-confining region and the trace of a phase point in the phase space for a particle orbit in an accelerator. The methods used for determining stability limits for particles in periodic accelerators are thus applicable to the problem of confining lines of force in stellarators and pinches. Examples are given and computer methods are described for typical stellarator configurations subject to a variety of field errors.

A steady state plasma in a magnetic field has been generated by an electron stream along magnetic field lines which passed through a neutral gas jet. Plasma turbulence was observed by a technique which removes the plasma ions without greatly disturbing their density distribution. In general, the amplitude of the turbulence was found to increase with the magnetic field strength. The magnetic field required for onset of turbulence increased with increasing ion mass. Transport of plasma across the magnetic field increased as the turbulence increased. A mirror magnetic field produced more turbulence than a uniform magnetic field, and a cusp magnetic field produced no turbulence in the plasma.

Theory using an equivalent permittivity approach predicts that a hollow cylindrical plasma column should have two resonance frequencies. Such frequencies had not yet been experimentally observed. Two hollow cylindrical discharge tubes of different sizes have been built with great care and have enabled the observation of two well-defined resonance peaks. The agreement between theory and experiments for both the frequencies and the amplitudes is very close.

A comparison with the ordinary cylindrical plasma column is made and it is suggested that the method used ought to give a quite satisfactory measurement of the average plasma density.

The dispersion equation of Cauchy integral type for longitudinal plasma oscillations in a magnetic field is for the first time exactly derived, in order to obtain the general instability criterion for magnetoplasma oscillations, on the basis of Vlasov's collision-free kinetic equation for arbitrary velocity distributions.

The motion of the ions is easily taken into account by replacing Φ(k,v) by ϕ_-(k,v) + ϕ₊(k,v)m_-/m₊. The terms important for the drift instability are provided.

The first two terms correspond to the dispersion relation either for the case of strong magnetic field approximation or for the case of grazing angle propagation. The third term contributes to the drift instability in the case of wave propagation at an appreciable angle to a finite magnetic field.

The fourth and higher order terms give rise to the instability due to anistropic velocity distributions. The criterion for plasma instability in a magnetic field is obtained using potential theory.

According to TIMAN (1954), the electrostatic interaction of ions in an ionized gas tends to favour ionization and at sufficiently high pressures the degree of ionization will start to increase with pressure.

By using some recently developed improvements of the Debye-Hückel theory, it is shown that, while in the case considered by TIMAN this effect does not occur at any pressure for which the theory is valid, it does occur at somewhat lower temperatures. One thus obtains a type of `pressure ionization' from a classical model without invoking volume-dependence of energy levels or similar effects.

The energy losses of an originally unmodulated electron beam during its passage through a plasma which is not in a magnetic field have been determined experimentally. With a current of 8 A, an energy of 26 keV and a plasma density of (-7 similar 9) × 10¹⁰ cm^-3, these losses amount to 12 per cent of the energy of the electron beam. It is shown that these large energy losses are due to the coherent interaction of the beam with the plasma.