Theoretical Investigation on Down-Taper-Type Frequency-Tunable Reflective Gyro-BWO

The effect of an upstream steep down taper added onto an interaction circuit with a single smooth down taper is investigated. Explorations of the physical mechanism reveal a twofold effect: enhancement of efficiency due to better electron bunching, and a shift in the optimal interaction phase. With the adoption of an additional down taper, the optimal phase for the highest peak efficiency shifts from 0° to 180°, suggesting the potential of efficiency-enhanced double down-taper circuits. Based on the elucidated mechanism, a piecewise frequency-tunable gyrotron is proposed, where a series of TE<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{0}{n}}$ </tex-math></inline-formula> modes tuning is expected to provide a wide tunable band across 320–480 GHz. This study contributes to the comprehension of reflective gyro-BWOs and facilitates further exploration of gyrotron oscillators toward the terahertz (THz) regime.