摘要
The gyrotron backward-wave oscillators (gyro-BWOs) feature a continuous frequency tunability in a single transverse mode, while the step-tunable gyrotrons are famous for their ultrawide frequency hopping between various transverse modes. This study proposed a reflective gyro-BWO with a piecewise-continuous and wide tunability. The frequency is tunable in one transverse mode and can be switched to another by changing the applied magnetic field or/and the beam voltage. Meanwhile, the high-order axial modes (HOAMs) inside a cavity with a low-Q factor could broaden the bandwidth of each transverse mode. The interaction structure is optimized for the TE&null and TE&null modes that serve as the principal operating modes. The adjacent TE&null and TE&null modes could be excited to broaden the overall tuning range by adjusting the operating parameters. The measured magnetic tunings show a wide bandwidth of 36 GHz from 182 GHz at 6.6 T up to 218 GHz at 8.0 T, which agrees with the numerical simulation predicted from the Computer Simulation Technology (CST). Besides, the measured voltage tunings exhibit a bandwidth of 2 GHz for the TE&null mode with a low-beam voltage from 12 to 19 kV. This study demonstrated that the reflective gyro-BWO could generate piecewise frequency tuning in four transverse modes and will be an excellent, moderate-power, terahertz source for many applications.