COHERENT EMISSION AND GAIN FROM A BUNCHED ELECTRON-BEAM

The radiation from a modulated electron beam, such as that produced in a radio-frequency accelerator, passing through a magnetic undulator i s analyzed. We show that in a waveguide FEL, this may lead to an emiss ion of a significant amount of coherent radiation in the far infrared to millimeter wave range. A simple and powerful method of calculating the spectral distribution of the radiated power is presented along wit h an analysis of the gain and the saturated power. The experimental re sults of spontaneous emission measurements on an RF driven FEL are pre sented and compared to theoretical predictions.