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.
