Electromagnetic ion-beam-plasma instabilities

It is well known that ion beam-plasma interactions can destabilize right- and left-hand polarized electromagnetic waves. However, these instabilities have been studied for frequencies less than the ion-beam gyrofrequency, with the exception of Goldstein and Wong (1987), and Brinca and Tsurutani (1988), who studied also the region of high frequencies (omega > Omega(i), where Omega(i) is the ion-beam gyrofrequency), in connection with pickup cometary ions. It has been recently demonstrated that in the cold plasma theory, left- and right-hand modes can be destabilized in a rather large range of frequency and wavenumber values. It has also been shown that, in some cases, the unstable spectrum has a band structure. We study here thermal effects on the cold modes and show that, as the temperature increases, the band structure becomes a double-humped unstable spectrum. For even larger temperatures, the double-humped structure is washed out, remaining a single-humped spectrum, but with an instability range which is similar to the cold plasma case. We then apply these results to the solar wind. (C) 1998 Elsevier Science Ltd. All rights reserved.