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.
