Often one is interested in the electrical conductivity of a plasma for frequencies of the applied electric field comparable to or greater than the effective collision frequency. For the purpose of obtaining an order of magnitude estimate of the conductivity a Lorentz gas model with a Fokker–Planck collision term is used. For this simple model a formula for the a.c. electrical conductivity for two limiting cases is derived in closed form. The first term of the expression for the conductivity in the case where w/k is very large agrees with that obtained by Bernstein & Trehan (1960) for the spatially homogeneous case, while the effect of the spatial gradients is indicated in the higher order terms. In the case where w and k are both equal to zero the expression for the d.c. electrical conductivity of Spitzer (1962) is recovered.

Solutions are obtained for cylindrical waves of the equations governing a magnetized self-gravitating collisionless plasma. Subject to certain conditions, we find two types of instability: (i) the hose instability which is related to the anisotropic pressure; and (ii) gravitational instability.

Transport coefficients are given in tabular form for partially ionized helium in chemical equilibrium at several pressures and for temperatures up to 35000 °K. Simplified theoretical expressions, derived with the Chapman—Enskog—Burnett method, were used for the computations. The convergence of the approximations to the electrical conductivity was also studied. It was found that the first approximation was within 17% of the true value at low ionization in contrast to recent results for argon where it could not be determined if even the fourth approximation had converged to the true value.

A kinetic theory is presented which is valid for both weakly unstable and stable plasma. The theory corrects the conventional Balescu—Guernsey—Lenard description for the weakly stable portions of the fluctuation spectrum. The theory is no longer Markoffian in the distribution function F alone but is in the pair F and Ik the spectrum of fluctuations. Further the evolution in time from an initially weakly unstable distribution to the stable regime can be described. Even after passage into the stable state the fluctuations can be large nd lead to enhanced diffusion across a magnetic field. The coefficient of spatial diffusion is given in this weakly stable (or untable) state. A strong coupling is found between plasmons and the particles in the distribution with velocities near the phase velocities of the plasmons. There is only weak thermal contact between the plasmons and these particles with the main body of the distribution whenever certain nonlinear processes are of secondary importance.

This paper concerns the time-dependent motions of the cavity formed when a uniform corpuscular flux is incident on the magnetic field of a line current. The two-dimensional problem is formulated and solved with two particular classes of solutions being given; namely, the steady-state solutions and the time-history of the interaction with a cloud of flux.

The motion of a charged particle in the field of a plane circularly polarized wave propagating along a uniform magnetic field B0 is investigated. For the wave magnetic field small compared with B0, the equations of motion simplify to those of the pendulum, and a simple picture of what happens for particles near gyro- resonance results. Expressions are found for the amplitude and period of the pitch angle oscillations. Departures from uniformity and possible applications to the magnetosphere are briefly discussed.

The microwave reflexion from and transmission around the shock-produced argon plasma whose electron density is greater than 102 times the critical electron density for the 9 Gc/s wave have been found to be similar to those of a metal rod. But the skin depth of the wave in the plasma plus the thickness of the shock boundary layer is found to affect significantly the amount of microwave power transmitted round the cylindrical surface of the plasma.

It is proved in the surface potential waves approximation that not oniy a bounded plasma with flows along the magnetostatic field, but also a plasma with a finite ‘longitudinal temperature’ of the electrons can be unstable against axially asymmetric perturbations of magnetohydrodynamic type. The branches of surface oscillations of a cold plasma, and the conditions for their excitation by an admixture of electrons with a sufficiently high ‘longitudinal temperature’ in various geometrical configurations, are also derived in the aper.

Conditions for the instability of longitudinal waves in a single-component two-stream plasma, in which the streams have the same velocity spread, are given in the form of simple relations between the density ratio and the mean velocity difference of the streams.

A pair of electrodes was placed in an electromagnetic shock tube to measure the electric field induced by the flow of an argon plasma through a transverse magnetic field. This investigation suggested that the plasma consisted of two regions, the first of which was non-luminous. Flow velocities, deduced from the variation of induced voltage with electrode separation, were compared with luminous front velocities measured photoelectrically. The first plasma region moved more slowly than the second, and its velocity and duration were consistent with shock-heating. The second region, which was dominant in most, experiments, flowed at the luminous front velocity, and had probably been ejected from the driver discharge. It is proposed that the flow velocity in the second region exceeded that in the first owing to an extensive leakage of gas through the boundary layer at the contact surface.