A gridded monotron of high efficiency

On the basis of analytical considerations and numerical simulation, this work demonstrates that the split-cavity monotron can reach an electronic efficiency of 40 percent. Following the design parameters provided by one-dimensional analysis, a 9.2 GHz monotron has been synthesized by properly selecting the radius (1.0 cm) and thickness (0.1 cm) of the coupling iris so that the resulting field amplitude (in the central shell of the annular beam) might reach the optimum saturation value of 40.0 kV/cm. The simulation with a 0.4-cm thick, 70-A current beam has given overall efficiency of 35.7% relative to 700 kW input beam power, with no self-consistent fields effects having been noticed at the nominal current density of 8.7 A/cm², about four times lower than the space-charge limit of 33.1 A/cm² for a 1.5-cm drift length and 10 keV beam. Although many issues remain to be examined the results achieved here demonstrate the capability of the split-cavity monotron as a high-power microwave tube in light of a newly discovered higher-efficiency regime.