On the dispersion of two coexisting nongyrotropic ion species

Space observations in the solar wind and simulations of high Mach number bo w-shocks have detected particle populations with two coexisting nongyrotrop ic ion species. We investigate the influence of these two sources of free e nergy on the stability of parallel (with respect to the ambient magnetic fi eld) and perpendicular propagation. For parallel modes, we derive their dis persion equation in a magnetoplasma with protons and alpha particles that m ay exhibit stationary nongyrotropy (SNG) and discuss the characteristics of its solutions. Kinetic simulations study the behaviour of perpendicular el ectrostatic (Bernstein-like) waves in a plasma whose ion populations (posit rons and fictitious singly-charged particles with twice the electron mass, for the sake of simulation feasability) can be time-varying nongyrotropic ( TNG). The results show that the coexistence of two gyrophase bunched specie s does not significantly enhance the parallel SNG instability already found for media with only one nongyrotropic species, whereas it strongly intensi fies the growth of Bernstein-like modes in TNG plasmas.