A new one-dimensional analysis of the collective interaction in a free-electron laser with combined helical wiggler and uniform axial magnetic fields is presented. Maxwell's curl relations and the cold-fluid equations are employed, with the appropriate form of solution for right and left circularly polarized electromagnetic waves and space-charge waves. A set of three linear homogeneous algebraic equations for the electric field amplitudes of the three propagating waves is derived. This set may be employed to obtain the general dispersion relation in the form of a tenth-degree polynomial equation. With the left circular wave assumed to be nonresonant, the dispersion relation reduces to a seventh-degree polynomial equation corresponding to four space-charge modes and three right circular modes. The results of a numerical study of the spatial growth rate and radiation frequency are presented.

Two secondary parametric instabilities providing cascade channels for the Langmuir sidebands of the oscillating two-stream instability (OTSI) and parametric decay instability (PDI), which are excited by O-mode high-frequency (HF) heating waves, are studied. The first one decays a Langmuir pump wave into a Langmuir sideband and an ion acoustic decay mode. Both resonant and nonresonant cascade processes are considered. Nonresonant cascade of Langmuir waves proceeds at the same location and is increasingly hampered by the frequency mismatch effect. Resonant cascade takes place in different resonant locations to minimize the frequency mismatch effect, but it has to overcome the severe propagation loss of the mother Langmuir wave in each cascade step. This process produces a narrow spectrum of frequency-downshifted (from the HP wave frequency) plasma waves. The second employs the lower-hybrid wave as the decay mode. Only the nonresonant cascade is of interest, because the propagation loss of the mother Langmuir wave in each resonant cascade step is far too severe. This is a three-dimensional coupling process, because the wavevectors of coupled three waves have to be matched in three-dimensional space, rather than matched in the conventional way on the plane of the pump wavevector and the geomagnetic field. A broad spectrum of frequency-downshifted plasma waves can be produced by this process in a narrow altitude range preferentially located near the matching heights of Langmuir sidebands of the OTSI and PDI.

New solutions are presented to the equilibrium Vlasov-fluid equations in Z-pinch geometry that include the effect of sheared axial ion flow. These are different to previous Vlasov-fluid equilibria in that the ion distribution function shows an axial temperature anisotropy. Examples of three new classes of equilibria are calculated, these being the anisotropic-parabolic (constant current density) and Bennett (constant relative speed) profiles and a set of profiles resulting from assuming that the ion fluid velocity is given by (b1+rp) for b1=−0.5 and p>1.

This paper examines the possibility of propagating surface waves in cylindrical plasma–plasma structures enclosed by metal walls and submitted or not to a static magnetic field. We consider the situation in which the inner plasma layer is overdense while the other is underdense. It is shown that outside the electron cyclotron resonance (ECR) conditions, the outer plasma layer plays a role similar to that of an ordinary dielectric layer, just modifying the wavenumber without drastically changing the general characteristics of the wave. At ECR, a major change in the wavenumber and attenuation coefficient is observed, a cutoff occurring on the left side of ECR and a resonance on the right side, provided the outer plasma density is large enough. It is further found that in conditions where the outer plasma layer thickness is very small, wave propagation still occurs, whatever the density value in this region. This suggests that surface wave propagation is possible in plasma–sheath–metal structures.