Gain Enhancement in Electromagnetically Pumped Free Electron Laser with a Guide Magnetic Field

An electromagnetic wiggler field is used as a pump in this work. A guide magnetic field is added to this configuration, since it is necessary in order to confine the beam against the effects of self field. A small amplitude backward electromagnetic wave is introduced as an additional perturbed electromagnetic wave, and first order perturbation analysis is applied. A small signal gain formula is derived for this system. Numerical calculations shows that this backward radiation field contributes for gain enhancement of the system when it approaches orbital instability. This enhancement of the gain is found within a new range of both the wiggler field amplitude and the perturbed frequency.