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

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+ similar to 1.36V(A) (V-A is the Alfven velocity), and the maximum growth rate is of the order of 10(-3)Ohm(p) (Ohm(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.