Minor heavy ion electromagnetic beam–plasma interactions in the solar wind

Abstract

It is shown that the velocity threshold of the right‐hand‐polarized ion‐ion resonant instability decreases with decreasing gyrofrequency values of the beam ions, and also, the system can become unstable for very small beam concentrations. In order to illustrate the results, a plasma consisting of a proton background and a very tenuous O + ion beam is considered. It is shown that for an ion beam of n O + / n p = 10 −4 , the threshold velocity is V O + ∼ 1.36 V A ( V A is the Alfvén velocity), and the maximum growth rate is of the order of 10 −3 Ω p (Ω p is the proton gyrofrequency). We apply these results to high‐speed solar‐wind‐type plasmas consisting of a proton background, an alpha particle beam, and a beam of O + ions. It is also shown that the presence of alpha particles reduces the velocity instability threshold of the O + ‐ p resonant instability.