THEORY AND COMPUTER-SIMULATION ON THE CURRENT-DRIVEN AND BEAM-DRIVEN ELECTROSTATIC INSTABILITIES IN THE AURORAL-ZONE

Abstract

According to satellite observations, strong ion acceleration transverse to the magnetic field (ion conics) may be a result of the electrostatic waves frequently observed in the auroral zone. A number of electrostatic waves are considered as possible candidates for perpendicular heating of ions. Both the linear and nonlinear theories of electrostatic instability driven by an electron current or an electron beam along the magnetic field using one- and two-dimensional simulations have been considered. For the current-driven case with T(e)=T(i), a two-stream-type electrostatic instability near the lower hybrid frequency omega approximately omega(pi) develops when the drift speed of the electrons exceeds the electron thermal speed. For the beam-driven case with T(i) approximately T(e) approximately T(b), it is clear that the beam drift speed must be much larger than the electron thermal speed in order for the beam inverse Landau damping to overcome both the electron and ion Landau dampings for the onset of the instability. For T(i) approximately T(e) much greater than T(b), the condition is relaxed because of the enhancement of inverse electron-beam Landau damping. Numerical simulation confirms the presence of both current- and beam-driven instabilities resulting in strong ion perpendicular heating.