Investigation on Thermal Efficiency Enhancement and Sideband Emission Suppression for Magnetron Injection Gun

At low-power operation, an approach with a capture structure is employed to absorb the trapped electrons for the $\textit {Ka}$ -band gyro-traveling wave tube (Gyro-TWT). When the power is further increased, the capture structure cannot play a role and the working current fluctuates. In subsequent experiments, the capture structure was found to have severe traces of melting. According to the position characteristics of the capture structure, the main reason for its melting is the phenomenon of sideband emission from the cathode of magnetron injection gun (MIG). In heat transfer systems of the conventional cathode, the rear electrode emits trapped electrons, which are accelerated by an electric field and bombard the capture structure. We adopted the scheme of adjusting the cathode heat transfer system. The enhanced cathode is called the isolated cathode (ISO-cathode). The test experiment proved that sideband emission is suppressed and thermal efficiency is improved. In the experiment, the cathode power decreased from 85 to 42 W when the operating temperature is at 1050 °C. In the end, the absorbed power of the capture structure is less than about 1/10 of the original power by simulation. The life and reliability of MIG are increased by ISO-cathode. The foundation is laid for further improvement on the average power by ISO-cathode.