Design and Experiment of a Compact Magnetron Injection Gun for a Coil Magnet X-Band Gyro-TWT

To achieve miniaturization and quick startup of the system, an investigation is carried out on a room-temperature coil magnet (CM) for the $\textit{X}$ -band TE(11 )mode continuous wave (CW) gyrotron traveling wave tube (gyro-TWT). The CM is capable of generating a maximum axial magnetic field of 0.4 T with a corresponding coil operating current of 90.2 A and power consumption of 23.5 kW. Then, a novel compact diode magnetron injection gun (MIG) based on the CM is designed, and its electronic characteristics are analyzed and discussed. The compact, curved-shaped MIG with a low magnetic compression ratio has a smooth rear electrode, nose front electrode, and curved emitter, which improve the electric field distribution to match the rapid variation of magnetic fields. A pitch factor of 1.28 and transverse velocity spread of 2.03% are obtained for an electron beam of 60 kV-10 A in the simulation. The radius of the cathode and anode are 5.8 and 24.4 mm, which is decreased by 42% and 50% compared to the previous MIG. A prototype cathode is fabricated and thermal analysis and experiments are performed. The test results show good agreement with the simulation, and the MIG exhibits good thermal stability after considering the thermal expansion.