A magnetohydrodynamic (MHD) wave, incident on the boundary between two MHD media in relative motion, may be amplified or attenuated by exchanging energy with the kinetic energy of the background flow. The conventional treatment of this problem uses a definition of the wave energy such that energy is conserved at the boundary. An amplified reflected wave then leads to the requirement of a transmitted wave carrying negative energy. Such an approach, while producing correct results, obscures the nature and location of the energy interchange. In this paper, the proper definitions of energy density and flux in a moving plasma are discussed, and the relationship of the group velocity and the energy flow is clarified. The mechanism by which energy is exchanged between streaming plasma and wave is through the work done by the Maxwell and Reynolds stresses on the gradient of velocity at the boundary. The location of the energy exchange is identified as the active boundary, with no need to invoke ideas of negative energy. The relationship between the two approaches is critically discussed.

The equations of magnetohydrodynamics (MHD) are written for non-uniform viscosity and resistivity – the latter in the cases of Ohmic and anisotropic resistivity. In the case of Ohmic (anisotropic) diffusivity, there is (are) one (two) transverse components of the velocity and magnetic field perturbation(s), leading to a second-order (fourth-order) dissipative Alfvén- wave equation. In the more general case of dissipative Alfvén waves with isotropic viscosity and anisotropic resistivity, the fourth-order wave equation may be replaced by two decoupled second-order equations for right- and left-polarized waves, whose dispersion relations show that the first resistive diffusivity causes dissipation like the viscosity, whereas the second resistive diffusivity causes a change in propagation speed. The second resistive diffusivity invalidates the equipartition of kinetic and magnetic energy, modifies the energy flux through the propagation speed, and also changes the ratio of viscous to resistive dissipation. If the directions of propagation and polarization are equal (i.e. for right-polarized upward-propagating or left-polarized downward-propagating waves), the magnetic energy increases relative to the kinetic energy, the resistive dissipation increases relative to the viscous dissipation, and the total energy density and flux increase relative to the case of isotropic resistivity; the reverse is the case for opposite directions of propagation, i.e. upward-propagating left-polarized waves and downward-propagating right-polarized waves, which can lead to the existence of a critical layer. The role of the viscosity and first and second resistive diffusiveness on the dissipation of Alfvén waves is discussed with reference to the solar atmosphere.

The effect of Coulomb correlations on the spectrum of electromagnetic waves propagating in a non-ideal magnetized fully ionized hydrogen plasma is studied. We employ the dielectric tensor constructed by means of the classical theory of moments without using perturbation theory.

The influence of a highly energetic electron beam on the electron distribution function (e.d.f.) in a hot dense plasma is investigated by solving the Boltzmann equation analytically. A plateau is obtained in the tail of the e.d.f. over an energy range between the excitation threshold and an energy value half that of the monoenergetic electrons. The importance of this plateau is discussed for a dense He-like argon plasma.

We examine the charging of dielectric dust grains embedded in a plasma. Our work is a continuation and refinement of our previous research into grain charging problems. In 1993, we discussed preliminary simulation results regarding the charging and intergrain forces between two dielectric dust particles [J. W. Manweiler et al., Adv. Space Res. 13, 10175 (1993)]. Then, in 1996, we discussed preliminary results with respect to dust grain charging within asymmetric plasma conditions and how these affect grain–grain collisional cross-sections [J. W. Manweiler et al., In: The Physics of Dusty Plasmas (ed. P. K. Shukla et al.), p. 22. World Scientific, Singapore (1996)]. This work was extended to evaluate how asymmetric charging affects coagulation rates for dielectric dust grains [J. W. Manweiler et al., In: Physics of Dusty Plasmas, 7th Workshop (ed. M. Horanyi et al.), p. 12. AIP Conf. Proc. 446 (1998)]. Here we report on the results of a significant refinement to our work to study the behaviour of a dielectric dust grain in a plasma with a bulk flow. Since charge transport is inhibited on our dielectric grains, we can examine how asymmetric plasma distributions affect the symmetry of the charge distributions that develop on the surfaces of the grains. A dielectric dust grain in a flowing plasma develops a negative total charge and a dipole moment in its charge distribution that points upstream. We also use this model to study how the presence of a nearby dust grain affects the development of a grain's charge distribution. We demonstrate that a smaller grain–grain separation results in a reduced net charge on each grain. For grains in a flowing plasma, dipole moments are unaffected by close approach except when one grain is directly in the ‘wake’ of the other grain. The studies here show that monopole and dipole electrostatic forces are present when dust is bathed in flowing plasma. Recent infrared studies suggest that a large fraction of young stars have dusty envelopes [G. Schilling, Science286, 66 (1999)]. In the formation of accretion discs around young stars, dust–plasma interactions are probably important. Full details on the calculations of the results discussed in this paper are summarized from a more complete treatment of the subject by Manweiler [PhD Dissertation, University of Kansas (1997)].

Transition radiation from the zone of injection of a modulated electron beam spiralling into a magnetoplasma has been identified as whistler waves propagating quasiparallel to the external magnetic field. The characteristics of the radiation are similar to the emission by localized sources, such as loop antennas and electric dipoles: resonance-cone structures at low plasma densities and energy flow along the external magnetic field at higher densities, with a diverging radiation pattern and with whistler phase velocities inversely proportional to the plasma frequency. These studies should contribute to a wider understanding of the physical processes connected with the injection of charges in a magnetoplasma – either from a gun on board a spacecraft or in a plasma chamber – and thus allow the determination of appropriate radiator characteristics in order to control, to some extent, plasma perturbations and wave emission in the region of the injector.