Excitation of electrostatic ion-cyclotron waves by an ion beam in a two-ion component plasma

Abstract

An ion beam propagating through a magnetized plasma cylinder containing electrons, light positive potassium ions (K+), and heavy positive cesium ions (Cs+) drives electrostatic ion cyclotron (EIC) waves to instability via Cerenkov interaction. Two EIC wave modes are present, the K+ and Cs+ modes. The unstable wave frequencies and the growth rate of both the light positive ion and heavy positive ion modes increase with an increase in their relative ion concentrations. The growth rate of both the unstable modes (K+ and Cs+) scales one-third power of the beam density. The real part of the frequency of both the unstable modes (K+ and Cs+) increases with the beam energy and scales as almost one-half power of the beam energy. Numerical calculations of the growth rate and mode frequencies have been carried out for the parameters of the experiment of Suszcynsky et al. [J. Geophys. Res. 94, 8966 (1989)]. It is found that the unstable wave frequencies of both the light positive ion and heavy positive ion modes increase with the magnetic fields in accordance with the experimental observations.