Effects of electron prebunching on the radiation growth rate of a collective (Raman) free-electron laser amplifier

Abstract

Experiments are reported on the effects of electron prebunching in a mildly relativistic, low-current (200-KV, 1-A) free-electron laser amplifier operating in the collective (Raman) regime at a frequency of approximately 10 GHz. Prebunching 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 radiation 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>