Radiation at 100 and 200 GHz From a Compact Planar Smith–Purcell Free-Electron Laser

In a recent experiment at 5 GHz, a Smith-Purcell free-electron laser equipped with lateral sidewalls emitted copious radiation at the fundamental frequency of the evanescent surface wave with 10% interaction efficiency. This was estimated using only the useful beam power, not the full beam power delivered by the generator. Theory shows that a rescaling of all grating parameters at constant energy leads to a rescaled wavelength for the emitted radiation. In this paper, we present the results of an experiment performed at CESTA at 100 GHz with a 1-mm period planar grating. The beam energy was 60 keV, beam current from 2 to 5 A. We estimated the output power at 100 GHz of about 200 W (for a 4-A beam), corresponding to an efficiency of 0.08%. Comparisons with the predictions from simulations are also included. The results of simulations to extend these results to higher frequencies are presented. This paper follows previous studies recently published in this journal with a cylindrical grating operating in the same range of frequency.