EFFECTS OF ELECTRON PREBUNCHING ON THE RADIATION GROWTH RATE OF A COLLECTIVE (RAMAN) FREE ELECTRON LASER AMPLIFIER

Experiments are reported on the effects of electron prebunching in a mildly relativistic, low current (200kV, 1A) free electron laser amplifier operating in the collective (Raman) regime at a frequency of %1OGHz. Pre-bunching is established by injecting an electromagnetic wave into a bifilar. helical wiggler and then transporting the bunched beam into a second magnetic wiggler region. The wave growth rate is deduced from measurements of the ra-diation intensity as a function of interaction length. Observations show that prebunching can increase the radiation growth rate manyfold as compared with a system without prebunching. Studies are presented both in the small signal (linear) regime, and in the nonlinear (saturated) regime