Self-Fields Effects on Gain in A Helical Wiggler Free Electron Laser With Ion-Channel Guiding and Axial Magnetic Field

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