Recent Results on Development of Sub-GW Long-pulse THz-band FEL

Project of high-power long-pulse sub-THz to THz-band FEL is under development in collaboration between BINP (Novosibirsk) and IAP RAS (Nizhny Novgorod) driven by the linac “LIU” of the new generation forming 5-20MeV/2kA/200 ns electron beam. The aim of this project is to achieve a record sub-GW power level and pulse energy content up to 10-100J at the specified frequency ranges. In the present paper, results of electron-optical experiments on the formation of an electron beam with parameters acceptable to drive the FEL are discussed. Helical pulse undulators were elaborated for pumping operating transverse oscillations of the beam electrons. As a key component of the electrodynamic system of the FEL-oscillator, the possibility of using advanced Bragg resonators based on the coupling of propagating and quasi-cutoff waves, which are capable to provide stable narrow-band generation under conditions of substantial oversize of the interaction space, is analyzed. Results of simulations and “cold” tests of resonators of this type for operation in the sub-THz range with a diameter of more than 20 wavelengths are presented.