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 ω Ω^p and k₀ = 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, ω Ω of similar conclusions reached by Pearlstein et al. (1966) and Farr & Budwine (1968), for ω-values equal to the first few harmonics of the proton gyrofrequency.