Study of 1-THz 4th-Harmonic Gyrotron

A preliminary design of a 1-THz gyrotron based on the forth harmonic operation is presented. The cylindrical-waveguide TE
_4,8
mode is selected as the operating mode. Considering the weak beam-wave coupling strength in a 4
^th
-harmonic open-cavity interaction circuit at the frequency of 1 THz, this paper proposes applying low-temperature cooling, for example applying liquid nitrogen, to increase the limit of the Q factor and extend the effective length of the cavity resulting in a significant enhancement of the interaction efficiency and suppression of ohmic losses. Applying multi-mode time-domain theory in the simulation, it was found that although the competing third-harmonic TE
_3,6
mode was excited first, the fourth-harmonic TE
_4,8
mode finally dominates in the steady state regime.