This paper describes the design of a triode magnetron injection gun for use in a 200 kW, 300 GHzgyrotron. As power and frequency increase, the performance of the gyrotron becomes quitesensitive to the quality of the electron beam. Formation of a laminar electron flow is essential forthe realization of a high quality beam with a small velocity spread. In this study, a new method isdeveloped for a quantitative evaluation of the laminarity and is applied to optimize the electrodedesign. The laminarity depends not only on conventional design parameters such as the cathodeslant angle but also on the spatial distribution of the electric field along the beam trajectory. Inthe optimized design, the velocity pitch factors, a, larger than 1.2 are obtained at 65 kV, 10Awith spreads, Da, less than 5%.
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