Accepted Wednesday Oct 21, 2009
A few years ago a new theory for producing coherent Smith-Purcell (SP) radiation from an initially continuous beam was proposed. This experiment confirms that two-dimensional theory. The beam was typically 10 cm wide, a few mm thick, with a peak current of 200 A and beam energy of 85 keV. The 10 cm-wide grating had twenty 2-cm periods, and radiation was produced at the fundamental frequency near 4.5 GHz. Second and third harmonics were observed at the expected angles. Beam bunching was measured using a Bdot probe placed at the end of a groove. Generally good agreement between this experiment and the 2-D theory is found.