Monte Carlo simulation of a finite thickness neutralized electron beam

Abstract

Cyclotron resonance maser (CRM) instability1–2 is characterized by the oscillation condition ω >Ω + k z V z , where the Doppler-shift term k z V z in the fast electron cyclotron mode ω =Ω + k z V z is negligibly small. Here, ω, k z , Ω = eB 0 /mγ 0 and V z are, respectively, angular frequency and wavenumber of oscillation, relativistic cyclotron frequency and beam velocity in the axial direction; whereas -e, B 0 , m, and γ 0 are respectively, the charge on the electron, axial magnetic field, mass of the electron, and the relativistic factor. The CRM instability, however, may not be the unique principle of cyclotron emission near Ω. Another principle of cyclotron emission different from the CRM instability was found to exist theoretically, if high-density electron beams were neutralized by ions3–4. It was named Cherenkov instability in azimuthal direction (CIAD) that was expected to arise at an oscillation frequency ω z > c. Here, c is the velocity of light in vacuum.