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Paper IPM / P / 7761  


Abstract:  
A relativistic theory for Raman backscattering in the beam frame of electrons is presented and is used to find the growth rate of a freeelectron laser (FEL), in the Raman regime. A one dimensional helical wiggler and an axial magnetic field are considered. The effects of static selfelectric and selfmagnetic fields, induced by the steadystate charge density and currents of the nonneutral electron beam, are taken into account to find the steadystate trajectories. The wiggler effects on the linear dispersion relations of the spacecharge wave and radiation are included in the analysis. A numerical computation is conducted to compare the growth rate of the excited waves with nonrelativistic treatment. It was found that selffield effects increase the growth rate in the group II orbits and decrease it in the group I orbits. However, the wiggler effects on growth rate are stronger and increase the growth rate on both group I and group II orbits. Next, the growth rate under an ionchannel guiding, instead of an axial magnetic field, under similar condition is calculated and is studied numerically.
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