International Journal of

In this paper, we have investigated the effects of self-fields on gain in a helical wiggler free electron laser with axial magnetic field and ion-channel guiding. The self-electric and self-magnetic fields of a relativistic electron beam passing through a helical wiggler are analyzed. The electron trajectories and the small signal gain are derived. Numerical investigation is shown that for group I orbits, gain decrement is obtained relative to the absence of the self-fields, while for group II orbit gain enhancement is obtained.

A relativistic theory for two-stream free electron laser (FEL) with a one-dimensional helical wiggler and ion-channel guiding in the presence of self-fields are presented. A dispersion relation (DR) which includes coupling between the electromagnetic and the electrostatic waves is derived from a fluid model, with all of the relativistic terms related to the transverse wiggler motion. This DR is solved numerically to study many unstable couplings among all possible modes. Numerical calculations are made to illustrate the effects of the self-fields on the unstable couplings. It is shown that the self-fields can produce large effects on the growth rate of the couplings.