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The effect of thermal anisotropies on the Drummond-Rosenbiuth two-stream ion cyclotron instability is studied. The properties of the instability are found to be dependent on the ratio of parallel electron temperature to perpendicular ion temperature, T∥e /T⊥ ι which can alternatively be viewed as the product ofT∥e /T⊥ ι and the ion anisotropyT∥e /T⊥ ιThe critical drift velocity decreases and the growth rate increases with T∥e /T⊥ ι. However, the dependence on T∥e /T⊥ ι becomes less sensitive as this temperature ratio increases, and, in the limit of T∥e /T⊥ ι>1, the instability becomes independent of the perpendicular temperatures.

The ins tability of the electromagnetic linearly polarized mode propagating perpendicular to the magnetic field is studied for a system composed of two colliding plasma streams, in each of which both the electrons and the ions are streaming at the same velocity . Based on the linearized Vlasov-Maxwel 1 equations and allowing for anisotropic temperatures, it is found that in the presence of streaming ions the instability can occur in very low-P plasmas . The higher the values of p, the streaming velocity, and the temperature ratios T(~ff/T~a nd T~/T J f, the more the plasma is susceptible to the electromagnetic instability . The ratio T" f /T, ) has negligible influence, except when the streaming velocity is smaller than the ion the rma 1 speed .It is found that for p values of order unity, the streaming ions, while greatly enlarging the range of unstable wave numbe rs, contribute negligibly to the maximum growth rate, which is typically of the order of the electron cyclotron frequency . A comparison with the growth rates of the electros tatic two-stream instability is made .

The instability of right-handed, circularly polarized electromagnetic waves, propagating along an external magnetic field (whistler mode), is studied for electron plasmas with distribution functions peaked at some non-zero value of the transverse velocity. Based on the linearized Vlasov-Maxwell equations, the criteria for instability are given both for non-resonant instabilities arising from distribution functions with no thermal spread parallel to the magnetic field, and for resonant instabilities arising from distribution functions with Maxwellian dependence in the parallel velocities. It is found that, in general, the higher the average perpendicular energy, the more is the plasma susceptible to the whistler instability. These criteria are then applied to a sharply peaked ring distribution, and to loss-cone distributions of the Dory, Guest & Harris (1965) type.