Space-charge limited magnetron injection guns for high-power gyrotrons

In this paper, we present the results of a space-charge-limited (SCL) magnetron injection gun (MIG) design, which is intended for use with a 500 kV, 500 A gyroklystron. The design performance is compared with that of a temperature-limited (TL) gun that was constructed for the same application. Both designs yield similar values for beam quality, namely, an axial velocity spread under 7% for an average perpendicular-to-parallel velocity ratio of 1.5. The peak electric field is 7% higher for the SCL design and the average cathode loading, at 7.6 A/cm², is about 27% higher than for the TL design. A disadvantage of the TL design is that realistic variations in emitter temperature or work function translate into azimuthal current variations that hinder the operation of the device. The SCL design should have a quite uniform azimuthal distribution of cathode loading and, therefore, should be a better electron beam source for many high-power gyrotrons.