Effect of beam premodulation on excitation of surface plasma waves in a magnetized plasma

A density modulated electron beam propagating through a vacuum magnetized plasma interface drives electromagnetic surface plasma waves (SPWs) to instability via Cerenkov and fast cyclotron interaction. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of the SPWs. The growth rate γ of the unstable wave instability increases with the modulation index (Δ) and is maximized for Δ=1. For Δ=0, γ turns out to be ∼4.32x1010 rad/s for Cerenkov interaction and ∼6.81x1010 rad/s for fast cyclotron interaction. The growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. In addition, the real frequency of the unstable wave increases with the beam-energy and scales as almost one-half power of the beam-energy.