Magnetron injection gun design for a Q-band 300 kW 30 A gyrotron traveling wave tube

This paper is intended to present the optimal design of a triode type magnetron injection gun (MIG) for a 300 kW, 30 A gyrotron traveling wave tube (gyro-TWT), which is operated at Q band fundamental TE01 mode. Based on the analysis of velocity ratio (VR) distribution along the emission strip (ES), a further optimization of cathode geometry on the basis of a preliminary optimized gun is performed, and a new cathode structure is proposed. Compared with initial optimal parameters, the new structure demonstrates a decline of transverse velocity spread (TVS) from 3.66% to 0.57% and longitudinal velocity spread (LVS) from 4.11% to 0.72%, while VR is maintained at 1.05. The achieved overall LVS reaches as low as 3.44% when considering cathode surface roughness and thermal temperature effect. The sensitivity study has been carried out by changing the gun parameters like anode voltage, beam current, and cathode magnetic field to ensure the practical operation stability.