Abstract
Ion cyclotron instabilities in a bounded cold beam-plasma system are considered, with an electron beam injected parallel to an applied uniform magnetic field. The conditions and the growth rates of the instabilities of both of the electromagnetic and the electrostatic ion cyclotron waves due to their interactions with the electron beam are obtained. The surface current created by an azimuthal dc spinning times the radial ac displacement of the beam is found to have a significant role on the electromagnetic growth rate, while the presence of warm plasma electrons is found to be essential for the electrostatic instability. It is shown that if the direction of the dc spinning of the beam is in the same sense as that of the plasma ion gyration, the electromagnetic instability is remarkably enhanced.

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