Selective Photonic-Structure Cavity for High-Cyclotron-Harmonic Gyrotrons

Typically, cavities of sub-terahertz electron cyclotron masers (gyrotrons) have oversized dimensions. That leads to a problem of the dense mode spectrum and, as a result, to a problem of the mode selectivity in the process of realization of gyrotrons operating at high cyclotron harmonics. Open (mirror) type systems have a much sparser mode spectrum than closed-type systems. We suggest a way to further reduce the mode spectrum by implementing a cavity based on a photonic structure formed by two parallel corrugated mirrors, which are considerably offset from being in front of each other so that no mode can be supported by mirror reflection from them. The operating mode is contained by backward reflection from the corrugated mirrors based on the (−1)st order diffraction mechanism. The proposed system has intrinsic dispersion compensation properties which make it usable in a wide (~20%) frequency band. Simulated characteristics of a 2D prototype are presented and possible application for a gyrotron operating at a harmonic of the cyclotron frequency is discussed.