3-DIMENSIONAL SIMULATION ANALYSIS OF A 3-CM WAVELENGTH FREE-ELECTRON LASER AFTERBURNER

We have simulated a 3 cm wavelength free-electron laser afterburner (F EL Afterburner) using two sets of parameters: one is for a 3-cm period wiggler and the other is for a 5.4 cm period wiggler. For the 3 cm pe riod wiggler, the input beam energy is 112.5 keV, and for the 5.4 cm p eriod wiggler the beam energy is increased to 290 keV to make the FEL Afterburner operate at the same frequency. It is found, from the simul ations, that the FEL Afterburner with a longer period wiggler has a hi gher power conversion efficiency: larger than 16% $ for the 5.4 cm wig gler while only about 9% for the 3 cm wiggler. It is also shown that t o enhance the interaction efficiency in the slow wave cavity, the slow wave number should be a little larger than the sum of the fast wave n umber and the wiggler wave number.