Obliquely Propagating Unstable Whistler Waves: A Computer Simulation

Obliquely propagating unstable electron cyclotron electromagnetic (whistler) waves have been studied with the aid of an especially designed computer simulation experiment. The plasma-wave system considered is homogeneous and infinite, and the plasma is taken to be a mixture of warm (bi-maxwellian) and cold populations. With no cold plasma, the rates of growth of the low k modes maximize for the case of parallel propagation (θ = 0°) and decrease as θ increases; for higher k modes, the opposite occurs. Changing from k space to ωspace the above results indicate that off-angle propagation tends to stabilize the low-frequency whistlers but to destabilize the higher-frequency ones. These results are consistent with linear predictions. In all cases, however, the total electromagnetic energy generated in the system decreases with increasing θ. When cold plasma is added to the system, the total generated electromagnetic energy can maximize for a non-zero propagation angle.