Stability of H(+) beams in the polar wind

The effect of energetic H(+) beams on the stability of the polar wind in the classical model is studied with regard to the excitation of electrostatic waves. Consideration is given to cases covering a wide range of electron-to-background temperature ratios and beam-to-background ion density ratios, assuming a relatively cold beam. The minimum beam drift velocity required to destabilize the plasma is determined by a combination of the Nyquist technique and a direct solution of the plasma dispersion equation. It is found that the plasma can be destabilized for relative drift energies less than about 1 eV. Also, it is shown that the plasma is less stable for large electron temperatures and for comparable ion and beam densities.