An experimental investigation of the disturbed flow field created by conducting bodies in a mesosonic, collisionless plasma stream is reported. Part 1 dealt with ion focusing by the body's plasma sheath and the subsequent filling of the near-wake void region. In part 2, the mid-wake region is investigated, where, for bodies of the order of a Debye length in size, the focused ion streams converge to form a significant current density peak on the wake axis. A parametric description is obtained of the behaviour of the amplitude, width, and position of this peak. The results also indicate that portions of the axial ion peak are created by additional mechanisms and that body geometry affects the mid-wake structure only when the sheath is sufficiently thin to conform to the shape of the body.

The fluid equations for electrostatic wave forms propagating at small angles to a constant magnetic field are investigated. Both ion cyclotron and charge separation effects are included. Numerical results are given for initial conditions which are consistent with soliton formation. These results show a hybrid nonlinear wave form containing oscillations which are identified as short-wavelength fast ion-acoustic waves and long-wavelength slow ion-acoustic waves. An approximate analytic analysis is performed using the Bogoliubov–Krylov–Mitropolskii perturbation method.

Resonant three-wave interaction in a spatially non-uniform magnetized fluid plasma is considered. We calculate the coupling coefficients Vj for wave propagation in arbitrary directions and demonstrate that new terms, which appear in Vj owing to the presence of density gradients, can dominate actual wave coupling processes.

Analytic solutions for cylindrical, rigid-drift equilibria were searched for by checking the invariance of the second-order, nonlinear differential equations of the line density and particle density under one-parameter Lie groups. No invariance was found for the cylindrical screw-pinch for the polytrope index γ ╪ 2 of the pressure equation of state. For the Z-pinch, the differential equation for the line density for arbitrary γ is invariant under one group and reduces by Euler's method to an intractable first-order, nonlinear differential equation. In the case of a θ-pinch, the nonlinear differential equations for the particle density and line density are invariant at least under the translation group. The particle density is found as an implicit function of the radial distance r, involving incomplete beta functions of the γth power of the particle density.

Stability of doublet plasmas in the Doublet III device against resistive axisymmetric MHD modes has been studied. The real characteristics of the device were modelled as accurately as possible. Thus, for example, the actual toroidal geometry was used, the field shaping coils (F-coils) which surround the plasma were included, and the location of real limiters was incorporated for determination of the plasma surface. We have used two parameters to model the plasma current distribution and the equilibrium boundary conditions: one describes the flatness of the current profile, the other describes the fraction of the poloidal plasma flux contained within the separatrix. Thus we have determined stability as a function of these two parameters. If the fluxes at the F-coils are kept fixed, there are stable as well as unstable regimes in this two-dimensional parameter space. If the F-coil fluxes are controlled to imitate the presence of virtual F-coils with fixed fluxes located closer to the plasma, it is possible to stabilize the plasma. This stabilization is discussed in the paper and numerical examples are given. Finally, the relationship between the results of this paper and experimental observations from Doublet III is discussed.

The penetration of an externally applied rotating magnetic field into a plasma cylinder is examined. Steady-state solutions of an appropriate set of magneto-fluid equations show that, provided the amplitude and rotation frequency of the field are suitably chosen, the penetration is not limited by the usual classical skin effect. The enhanced penetration of the rotating field is accompanied by the generation of a unidirectional azimuthal electron current which is totally absent in a purely resistive plasma cylinder.

The generation of a steady azimuthal current in a cylindrical plasma column using a rotating magnetic field is numerically investigated. The mixed initial-boundary-value problem is solved using a finite difference method. It is shown that substantial azimuthal current can be driven provided that the amplitude of the rotating magnetic field is greater than a certain threshold value which depends on the plasma resistivity.

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.

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 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.

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.

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.

The Editor regrets that the following lines were inadvertently omitted from the Author Index for Volume 22, which appeared in the issue of December 1979.

Boyd, T. J. M. See Turner, J. G. and Boyd, T. J. M.

Johnston, S. and Kaufman, A. N. Oscillation centres and mode coupling in non-uniform Vlasov plasma, 105

Kaufman, A. N. See Johnston, S. and Kaufman, A. N.

Turner, J. G. and Boyd, T. J. M. Soliton formation in magnetoactive Vlasov plasmas, 121