The influence of negatively charged heavy ions on Alfven waves in a cometary environment

Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of Alfven waves in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species has been modeled by drifting distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution is simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies ( and being respectively the Doppler shifted and hydrogen ion gyro-frequencies ), the peak growth rate increases with increasing negatively charged oxygen ion densities. On the other hand, for frequencies (being the oxygen ion gyro-frequencies) the region of wave growth increases with increasing negatively charged oxygen ion densities.