Theory and design of terahertz-range second harmonic gyrotron with a two-mirror echelette-type cavity and transverse energy extraction

We propose a gyrotron scheme with a two-mirror echelette-type resonator to obtain high-power continuous wave terahertz (THz) radiation, in which a corrugated profile applied to one of the mirrors is specified in the transverse plane (with respect to an electron's translation velocity). The gyrotron has been driven by a sheet helical electron beam (2 A/20 keV) with a pitch-factor of 1.2 and acceptable velocity spread formed by a planar magnetron-injection gun. The theoretical analysis was carried out both within the framework of a self-consistent theory and on the basis of 3D particle-in-cell simulations. The linear and nonlinear stages of electron–wave interaction were analyzed. Simulations demonstrate the operability of the proposed gyrotron circuit in the frequency range of 0.79 THz, operating at the second cyclotron harmonic with a magnetic field strength of 15 T at the high-order TE0,50,1 mode. The output power level in the steady-state single-mode oscillation regime reached several kilowatts with an Ohmic loss value of less than 20%. Proof-of-principle experiment was carried out to study the selective characteristics of a two-mirror echelette-type resonator in the G-band, demonstrating the feasibility of the proposed gyrotron design.