Stimulated collective scattering from a magnetized relativistic electron beam

Abstract

We analyze stimulated scattering of a right-circularly-polarized electromagnetic pump wave, of frequency ${\omega }_0$, from a cold relativistic magnetized electron beam. The pump wave is chosen to satisfy the dispersion relation associated with the magnetized beam. The scattered waves consist of collective plasma oscillations as well as right- and left-polarized electromagnetic waves, traveling parallel and antiparallel to the beam. The frequency of the forward-scattered electromagnetic wave is Doppler shifted up twice and is of order ${{\gamma }_{0z}}^2{\omega }_0$, where ${\gamma }_{0z}={(1-\frac{v_0^2}{c^2})}^{-\frac{1}{2}}$ and $v_0$ is the beam's speed. Enhanced stimulated scattering results if the frequency of the pump, in the beam frame, is approximately equal to the electron's cyclotron frequency. Enhanced growth rates for the scattering process are obtained for the scattered radiation. This theory describes a mechanism which is a plausible explanation of a recent experiment in which ∼ 100 kW of submillimeter radiation was observed. In view of the large up-conversion in frequency and enhanced growth rates of the scattered radiation, a new high-frequency generative device based on this mechanism seems possible.