Design and experiment of an inverse magnetron injection gun for a Ka-band gyro-TWT with non-superconducting magnet

A triode inverse magnetron injection gun (IMIG) for a Ka-band gyrotron traveling wave tube (gyro-TWT) with non-superconducting magnet is proposed in this paper. Nowadays, the applications of gyro-TWT are intended to expand to moveable and fast-startup systems, so room-temperature magnet and system miniaturization are necessary. For a Ka-band gyro-TWT, to adapt to a room-temperature magnet with 20 mm bore radius, the IMIG form is adopted. Compared with conventional MIG, the gun maximum radius is reduced by 44%. On one hand, a curved emitter and cathode steps are utilized for better beam quality. On the other hand, isolation gaps and a cooling structure are designed to suppress stray electrons. A velocity ratio of 1.14 and a transverse velocity spread of 2.43% are obtained finally. The stray electrons are analyzed, and the IMIG tolerance is also evaluated. Finally, the cathode is fabricated, and its surface morphology is tested. It is then assembled into a gun shell, and the cathode temperatures are measured under both no cooling and cooling conditions. When the temperature of the emitter reaches 1050 °C, the heat powers are 84 and 115 W, respectively. The temperatures of the inner and outer electrodes are low enough to reduce the proportion of stray electrons.