High-frequency ion electrostatic instabilities in mixed warm-cold plasma

It is shown that an ion loss cone distribution function with m ⩾ 1 becomes unstable against electrostatic waves with w ≫ Qp and ka = 0 in the presence of a cold plasma population, in contrast with pure warm systems, which require m=3 for instability. This result is an extension to high frequencies, <w=Qp, of similar conclusions reached by Pearlstein et al. (1966) andFarr&Budwine (1968), for w-values equal to the first few harmonics of the proton gyrofrequency.