Published online by Cambridge University Press: 13 March 2009
Electrostatic instabilities excited by an energetic ion beam injected at an arbitrary angle with respect to the magnetic field in a collisionless plasma are discussed. Threshold conditions on the angle of injection and on the beam density are derived for the cross-field ion-ion mode, the modified two-stream mode and the ion-acoustic modes. The time evolution of the momentum and the thermal energy of each plasma component in the presence of the instabilities is calculated from moments of the quasi-linear equation. The background ions are significantly heated by most of the waves, exceptions being the modified two-stream mode and the resonant ion-acoustic mode. A wave with phase velocity close to the slow ion-acoustic wave has been found when the beam has a small density and a velocity greater than the acoustic speed by approximately a factor of five.