The Regime of the Efficiency Increase by Use of Long Circuits in the THz Cherenkov Oscillator

The self-consistent problem of electromagnetic (EM) field excitation by a rectilinear electron beam moving along either uniform grating Smith–Purcell radiation (SPR) or bi-periodic grating (leaky wave radiation of spoof surface plasmon polariton) and the influence of the excited EM field on the electron beam has been considered. It is shown that a deceleration of electrons (energy transfer from electrons to EM wave) in both the Smith–Purcell radiation and the leaky wave radiation of the spoof surface plasmon polariton regimes may occur for essentially increased slow wave circuit length in comparison with conventional backward wave oscillator (BWO) and orotrons. This allows either to enhance the output power or to reduce the beam current density of the THz oscillator. The simulations show the output power of 18 W with the corresponding efficiency of 1.5% at 0.64 THz in the case of the circuit length of 28 mm while the current density is 180 A/cm2. Such operation is based on the hybrid bulk-surface mode (HBSM) excitation in the THz oscillator cavity with bi-periodic grating and the top reflector for leaky waves. This is promising for the increase of the output efficiency higher than 1% and providing the Watt level of output power in the THz oscillator based on hybrid bulk-surface modes.