Free electron laser theoretical study

This is the final report of the Free Electron Laser Theoretical Study carried out by TRW for the AFOSR during the period July 80 to September 81. Four distinct but interrelated problems that play an important role in the characteristics of a Free Electron Laser oscillator were investigated: (1) Transverse Effects: The effect of wiggler field inhomogeneity as well as the influence of different transverse profiles of the signal field and the electron beam on the FEL characteristics were studied in detail. A dramatic decrease in gain and efficiency is found with increasing value of the ratio of electron beam radius to photon beam radius. (2) Small Signal (SS) Gain: A1-D investigation of the small signal gain for a Tapered Wiggler Free Electron Laser was performed analytically for cold electron beams and numerically for cold and warm electron beams. It was found that the small signal gain spectrum shifts and decreases in amplitude as a function of increasing wiggler taper. (3) Multicomponent Wiggler Free Electron Laser (MCWFEL): The results from (1) and (2) motivated the development of a new FEL configuration that could have high small signal gain and sufficiently high efficiency at high powers with nearly the same output frequency. The new FEL is a combination of several wiggler components. (4) Finite Pulse Length Simulations and Kinetic Effects of Trapped Particle Instabilities in Free Electron Lasers: A 1-D finite pulse code was developed and the effects of pulse slippage detrapping of electrons at the beam edge and parasitic instabilities investigated for a tapered wiggler Free Electron Laser.