We study the stability of the ion-acoustic (IA) wave in a collisional plasma composed of hydrogen, positively and negatively charged oxygen ions, electrons and neutral atoms. This composition approximates very well the plasma environment around a comet. A solution of the dispersion relation yields a frequency for the IA wave at around the hydrogen plasma frequency. The growth/ damping rate is sensitively dependent on the ring parameters u⊥s (the ring speed) and vts (the thermal spread). The growth rate of the wave, which decreases with increasing collisional frequencies, is larger when u⊥s ＜ vts . In the presence of negatively charged oxygen ions, the phase and group velocities of the IA wave behave in a contrasting manner when u⊥s ＜ vts (and viceversa). We propose that this behaviour be exploited as a diagnostic tool for the detection of these ions and also their thermalization.
Cite this paper
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