Nonlinear development of the ion-cyclotron electromagnetic instability

Cornwall et al. (1970) suggested that if the ring current protons penetrated the plasmapause, intense resonant electromagnetic ion cyclotron turbulence would lead to their rapid precipitation loss. In this paper we present a computer simulation study of the electromagnetic iow-cyclotron instability in a homogeneous plasma consisting of protons and electrons embedded in a static magnetic field, BOx. The plasma parameters used are KTpA = 25 keV, /3p<l = 8nnpKTPJIBlx = 1 and TPiJTPJ = 5. Effects such as sources and losses or space non-uniformities are not considered here. The predictions of the linear theory for the fast build-up of unstable left-hand (proton-like) electromagnetic ion-cyclotron waves are fully confirmed. The quasi-linear and nonlinear developments of the instability are followed in time to a state of quasi-equilibrium (from a collective point of view) in which Tp±ITPJ ~ 1-3. The nonlinear analysis includes the correlation between the relative energy density in the electromagnetic waves, thermal anisotropy, parallel and perpendicular velocity distribution functions and the pitch-angle distribution function.