OBSERVATION OF COHERENT SMITH-PURCELL RADIATION USING AN INITIALLY CONTINUOUS FLAT BEAM

A few years ago, a new theory for producing coherent Smith-Purcell (SP) radiation from an initially continuous electron beam was proposed. It was two-dimensional (2D), and it has been supported by 2-D particle-in-code simulations. We report here the results of an experiment using an intense continuous flat beam that confirms the theory. A maximum voltage of 100 kV was supplied by a single-shot pulsed-power source. The beam was typically 10 cm wide and a few mm thick, with a peak current of 150 A. The lamellar grating had twenty 2-cm periods, and radiation was observed at the predicted fundamental grating mode frequency near 4.5 GHz. The second and third harmonics were also observed at the angles predicted by the SP formula. Direct evidence for beam bunching was obtained using both a current monitor and a pick-up loop placed at the end of a groove. In general, good agreement between this experiment and theory is found.