Stimulated emission by E×B drifting electrons grazing a diffraction grating

It has been recently proposed that generation of relativistically upshifted radiation by an E×B drifting electron beam grazing a diffraction grating combines the Smith-Purcel free-electron laser (FEL) merits of short wavelengths at low beam energies, with efficiencies much higher than the 1/2 N_g conventional FEL limit. The small-signal theory is studied here, including the effect of drift velocity shear from the equilibrium (unbunched) space-charge fields. The dependence of the small-signal gain on the device parameters is determined and the startup current is evaluated. The effect of thermal beam spreads is analyzed and found that the oscillation startup current is much less sensitive to thermal spreads than a similar grating FEL