Controllable Thermal-Frequency Tuning of a Terahertz Gyrotron.

Gyrotron performance is sensitive to cavity structure parameters, and the cavity shape is temperature dependent due to thermal deformation induced by temperature rise fromohmic loss power on finite-conductivitycavity wall. Accordingly, this paper studies a frequency-tuning scheme for terahertz gyrotron by properly controlling the cavity thermal deformation. By combining gyrotron nonlinear theory and finite-elementmethod software, controllable thermal-frequency-tuning capability of a continuous-wave 263-GHz gyrotron is systematically investigated, toward maintaining gyrotron operating under gyromonotron condition in frequency-tuning band, and achieving high effi- ciency in broadband frequency-tuning range. After studying cavity thermal distribution, structure deformation, and electron beam--wave interaction, an optimized cavity structure with transition sections on both ends is proposed. Simulation predicts that with the two-transition-section cavity, via additional thermal tuning, the continuous-frequency-tuning band is capable of reaching 1.75 GHz, which is 5 times of the initial bandwidth. Furthermore, using the thermalfrequency- tuning technology, impressive high efficiency above 17% is obtainable in the whole frequency-tuning range. [ABSTRACT FROM AUTHOR]