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A self-excited vertical oscillation of dust grains in the sheath region of an rf-discharge plasma has been observed. The variation of amplitude with pressure and input power was measured. Dramatic increase of oscillation amplitude was found for pressures below 4.5 Pa. Possible excitation mechanisms are considered.

The nonlinear amplitude modulation of electromagnetic waves propagating in pair plasmas, e.g., electron-positron or fullerene pair-ion plasmas, as well as three-component pair plasmas, e.g., electron-positron-ion plasmas or doped (dusty) fullerene pair-ion plasmas, assuming wave propagation in a direction perpendicular to the ambient magnetic field, obeying the ordinary (O-) mode dispersion characteristics. Adopting a multiple scales (reductive perturbation) technique, a nonlinear Schrödinger-type equation is shown to govern the modulated amplitude of the magnetic field (perturbation). The conditions for modulation instability are investigated, in terms of relevant parameters. It is shown that localized envelope modes (envelope solitons) occur, of the bright- (dark-) type envelope solitons, i.e., envelope pulses (holes, respectively), for frequencies below (above) an explicit threshold. Long wavelength waves with frequency near the effective pair plasma frequency are therefore unstable, and may evolve into bright solitons, while higher frequency (shorter wavelength) waves are stable, and may propagate as envelope holes.

The radial structure of a low-pressure cylindrical post-cathode direct-current magnetron discharge is investigated using a one-dimensional, electrostatic particle-in-cell code, incorporating non-periodic boundary conditions and an external circuit. Electron and ion collisions with a background gas of argon are modelled using Monte Carlo techniques. The radial structure of the discharge is examined for a range of operating conditions. Profiles of the electric potential, electric field and space charge density are found to vary systematically with the pressure p and magnetic field strength B, in a way which corresponds to a transition from the usual positive space charge mode at low values of B/p to a higher impedance negative space charge mode at higher values of B/p. This is consistent with a continuous and considerable reduction in the ratio of the electron-to-ion classical cross-field transport coefficients with increasing B/p. Results of a fluid model also predict the transition to the negative space charge mode.