Reaching high frequencies in a Smith-Purcell FEL with a multi-channel grating

Summary form only given. Three-dimensional simulations and experiments have shown that, for a grating equipped with sidewalls, copious emission of coherent Smith-Purcell (SP) radiation at the fundamental frequency of the evanescent surface wave is possible. One may reduce the wavelength by rescaling all the parameters of the grating, but this reduces the radiated power by the square of the scale factor. Both 3D MAGIC simulations and the theory of antenna arrays suggest that by laterally juxtaposing N copies of the N-fold reduced grating, the overall power reduction is only 1/N. Furthermore, the radiation is concentrated into a solid angle of size 1/N compared to that of a single reduced grating. An experiment at 32 GHz partially confirms these predictions for N = 7. Preliminary simulations indicate that with a single 20-fold reduced channel coherent Smith-Purcell radiation at 100 GHz is produced. An experiment to confirm that a 20-channel grating will produce a well-collimated radiation pattern with adequate power levels is being prepared.