Towards high frequency operation with multi-grating_Smith Purcell FELs

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^{1, 2}. This contrasts with the two-dimensional theory for which emission could only occur at harmonics of that frequency. To increase the emitted frequency towards the THz range with a realistic electron beam, we propose to use several gratings with sidewalls in parallel, with adequate scaling of their parameters. Simulations suggest that the reduction in power, due to the reduced grating period and width needed to reach high frequencies, can be compensated in this way. To test this idea, an experiment is under way.