REPORT ON FIRST MASING AND SINGLE-MODE LOCKING IN A PREBUNCHED BEAM FEM OSCILLATOR

The effects of electron beam prebunching on the radiation buildup proc ess in a free electron maser oscillator operating in a collective-Rama n regime and oscillating in the frequency range of 4 to 5 GHz are stud ied. An electron beam is prebunched, accelerated to 70 keV, transporte d through a drift region, and injected into a linearly polarized wiggl er in which FEL interaction takes place. Single-frequency selection an d locking due to electron beam prebunching is demonstrated; we show th at the electron beam prebunching can be used to force the oscillator t o achieve steady-state single-mode operation and to select the oscilla tor frequency to be any of the resonator natural frequencies of the ca vity in net gain bandwidth. An appreciable speed-up of the oscillation buildup due to prebunching was also observed.