Simultaneous emissions at nωc and (n+1/2)ωc in space and laboratory plasmas

Experiments done in space and laboratory on the interaction of an electron beam and a magnetized plasma exhibit the simultaneous excitation of waves near harmonics and half harmonics of the electron gyrofrequency. The dispersion equation for electrostatic modes has been solved for an anisotropic Maxwellian plasma and a suprathermal population (``beam'' in the text) presenting anisotropy and regions of ∂f₀/∂v_⊥>0 in its distribution function. For oblique propagation to the magnetic field, results similar to those observed in experiments are obtained. The hydrodynamic/kinetic nature of the instabilities is discussed.