Cyclotron Emission from a Finite Thickness Neutralized Electron Beam

Abstract

Cyclotron emission from a neutralized, large orbit (LO), and finite thickness monochromatic electron beam in the presence of a right hand circularly polarized field of a plane electromagnetic wave is studied. Trajectories of N=50000 electrons whose gyration centers are randomly distributed within a circle of radius △, as well as their initial position that too are randomly located on their LOs, are followed. A restoring force caused by neutralizing ions is effective for electrons leaving the outer or the inner radii of the finite thickness beam. This force is introduced by a phenomenological potential well in the radial directions as was done previously for an infinitesimally thick beam [J. Plasma Phys., 73, 523{541, (2006)]. It is shown that for the beams having high density, the Cherenkov instability in the azimuthal direction (CIAD) with ω＜Ω+kzVz causes the excitation of microwaves. With an increase in the beam thickness, the CIAD decreases and finally stops. Beyond this thickness, the cyclotron maser instability for ω＜Ω+kzVz causes the generation of microwaves.