New Performance of Far Infrared Waveguide Free Electron Laser Driven by RF Linac

We present a modes expansion method that is used to calculate spontaneous emission radiated by the radio – frequency (RF) modulated short pulse electron beam, which the radiation is confined in the rectangular waveguide. The modes expansion coefficients determine the radiation power into the TE0n modes. Taking the short pulse as an ideal delta function on time scale, we find that the radiation field pattern is just of the 損ure?waveguide modes if the resonance frequency equals as integral times as radio frequency. Finally, evaluating the power of Shanghai RF far infrared waveguide free electron laser which is being designed is performed.