Improved Power Capacity in a Low-Magnetic Field and High-Efficiency Transit-Time Oscillator by a Double-Gap Extractor.

With an increase in the input power of a low-magnetic field and high-efficiency transit-time oscillator, the deceleration electric field in the single-gap extractor increases sharply to output a higher-power microwave, resulting in radio frequency breakdown on the surface of the single-gap extractor. Thus, a double-gap extractor with an operating mode of pi mode is introduced to reduce the electric field in this type of device. The double-gap extractor can extract electron energy in two stages and lengthen the deceleration distance. Therefore, the electron beam loses less energy at the same deceleration distance in the double-gap extractor, and a weaker deceleration electric field is generated in the double-gap extractor. Additionally, the modulation electric field in the device with a double-gap extractor is stronger for modulating electrons and can further increase the fundamental harmonic current, resulting in higher extraction efficiency. In simulations, the output power is 6.3 GW and the maximum electric field strength is 1.06 MV/cm in the initial model with a single-gap extractor. When the single-gap extractor is replaced by the double-gap extractor, the output power increases to 6.5 GW with a conversion efficiency of 40% and a guiding magnetic field of 0.6 T. The maximum electric field strength decreases to 817 kV/cm, indicating an enhancement in the power capacity of the device.