Electron cyclotron masing and the force due to net stimulated bremsstrahlung in an electron cyclotron maser using a dilute non-relativistic electron beam

The amplification of an electromagnetic wave by net stimulated bremsstrahlung (the emission by stimulated bremsstrahlung minus the absorption by inverse bremsstrahlung) injected into a non-relativistic dilute electron beam travelling in a uniform magnetic field is considered. The d.c. ponderomotive force by net stimulated emission is calculated by using quantum kinetics. From the calculated ponderomotive force, the amplification of the intensity of the electromagnetic wave by the net stimulated bremsstrahlung is derived as a function of the relevant parameters of the electromagnetic wave and the electron beam. It is found that masing is possible when the perpendicular temperature of the electron beam is greater than its parallel temperature. It is shown that the efficiency of a practical gyrotron cannot be explained by the phase-bunching concept, and that simulated bremsstrahlung has nothing to do with any phase bunching.