Investigation of a Magnetron Injection Gun With an External Anode for Ka-Band Gyro-TWT

In this article, a diode magnetron injection gun (MIG) with an external anode for Ka-band gyrotron traveling wave tubes (gyro-TWTs) is designed, whose anode is demountable. The magnet bore radius constrains the maximum radius of an MIG. To adapt to a magnet with smaller bore radius, a compact MIG with smaller radial size is necessary. Compared to the previous conventional Ka-band MIG, the gun effective radius constrained by the magnet bore is reduced from 35 to 19.5 mm, which is a 44% reduction. For a better high-voltage insulation performance of the MIG, studies are conducted on its three-layer dielectric separately: corrugated ceramic is used between the cathode and the anode, and the external anode is immersed in insulating oil. Additionally, a capture structure is designed to suppress backflow electrons. The velocity ratio and transverse velocity spread of the final MIG are 1.36% and 2.19%, respectively. Due to the replaceability of its anode, the MIG has potential for application in multiband or pulsed-continuous wave gyro-TWT operations. To verify the high-voltage stability of the MIG with an external anode, a high-voltage insulation experiment is carried out. The experiment reveals that no breakdown occurs at the operating voltage of 48 kV in the MIG.