Influence of self-electric and self-magnetic fields on coupling of waves in free electron laser with background plasma

In this study, waves instability in free electron laser with background plasma, under the influence of self-electric and self-magnetic fields, are analyzed. A dispersion relation in the Raman regime for free electron laser with a helical wiggler magnetic field and an axial magnetic field derived in which all possible wave modes can have unstable couplings with each other. This dispersion relation is solved numerically to investigate the influence of self-fields on unstable couplings. It was found that self-fields reduce the growth rate of the group I orbits and increase it in the group II orbits