Electrostatic Ion Cyclotron and Ion Acoustic Wave Instavilities Driven by Upgoing Oxygen Ion (O⁺) Beams on Auroral Field Lines

An investigation is made on the instabilities of electrostatic oxygen ion (O⁺) cyclotron and ion acoustic waves in a model plasma consisting of background hot electrons, background cold protons (H⁺), and strongly anisotropic oxygen ion beams. It is shown that the lower frequency and electrostatic O⁺ ion cyclotron and ion acoustic waves may be excited by upgoing O⁺ ion beams on auroral field lines. Upgoing O⁺ ion beams may be an important source of free energy for the lower frequency and electrostatic instabilities on auroral field lines.