Stimulated scattering of waves in microwave generators with high-current relativistic electron beams: simulation of two-stage free-electron lasers

Abstract

Abstract A theory of stimulated scattering of electromagnetic waves by high-current relativistic electron beams is developed, with the transverse inhomogeneity of incident and scattered waves, the presence of a magnetic field focusing the particles and a space-charge field taken into account. The characteristic features of stimulated scattering that occurs directly in the interaction space of a powerful relativistic pump wave oscillator based on Cerenkov radiation of a high-current electron beam are studied. It is shown that the electro dynamicsystem of such an oscillator in the form of a cylindrical waveguide with a periodically corrugated wall can have a high Q-factor for oscillations at wavelengths much shorter than the corrugation period. The relativistic 3 –cm backward wave oscillator (BWO) provided powerful scattered radiation at 3–8 mm with integral power up to 50 MW. The mechanisms competing at the onset of shortwave generation in the electrodynamic system of Cerenkov oscillators are discussed: (i) stimulated Smith-Purcell radiation, and (ii) stimulated undulator radiation of particles in an electrostatic field produced by the high-current beam. The first mechanism was studied experimentally. The FEM oscillator based on stimulated Smith-Purcell radiation was realized in a single-mode regime at a wavelength of 5 mm with a power of 20 MW and efficiency up to 5 per cent.