Ion beam driven ion-cyclotron waves in a plasma cylinder with negative ions

Abstract

An ion beam propagating through a magnetized plasma cylinder containing K+ positive ions, electrons and SF6− negative ions drives electrostatic ion-cyclotron (EIC) waves to instability via Cerenkov interaction. Two EIC wave modes are present, the SF6− and K+ modes. The frequencies and the growth rate of both the unstable negative ion and the positive ion modes increase, with increasing ε (=nSF6−/nK+), the relative density of negative ions. The frequencies of both the unstable modes (SF6− and K+) increase, with the magnetic field. The growth rate of both the unstable modes (SF6− and K+) scales as the one-third power of the beam density. The real frequency of both the unstable modes increases as almost the square root of the beam energy. Numerical calculations of the growth rate and modes frequencies have been carried out for the parameters of the experiment of Song et al. [Phys. Fluids B 1, 2316 (1989)] and the results are in good agreement with the experimental observations.