Linear and nonlinear analysis of the cyclotron two-stream instability

A two‐dimensional, self‐consistent, nonlinear model is used to determine the growth rate and saturation level of the cyclotron two‐stream instability for two weakly relativistic electron beams copropagating along a uniform magnetic field with an inverted population in the perpendicular momentum. This instability has been proposed recently as the basis for a double‐stream cyclotron maser. Good agreement is found between the dispersion analysis and computer simulations in the linear regime. The effect of axial momentum spread on the instability is investigated. It is shown that the cyclotron two‐stream instability is primarily electrostatic, which calls for further exploration of an effective input and output coupling scheme for the maser.