The effects of self-fields on the electron trajectory and gain in a two-stream electromagnetically pumped free-electronlaser with axial guiding field

A theory of a two-stream free-electron laser in a combinedelectromagnetic wiggler (EMW) is developed, in which we use anaxial-guide magnetic field and take into account the effects of theself-fields. The electron trajectories and the small signal gain arederived. The stability of the trajectories, the characteristics ofthe linear-gain, and the normalised maximum gain are studiednumerically. The results show that there are nine stable groups oforbits in the presence of self-fields instead of seven groupsreported in the absence of the self-field. It is also shown thatthe normalised gains of four groups of the orbits are decreasing andthose for the rest of them are increasing with growing $bar{varOmega }_0 $. Furthermore, it is found that the two-streamlaser with self-field enhances the maximum gain in comparison withthe single stream case.