Design criteria for high-density hollow-beam electron guns

Over the past few years there has been an ever increasing interest in microwave tubes of higher average power capability. At an average power level of roughly 5 to 10 kW (at X-band), even a well -focused, solid electron beam becomes of marginal utility for use in a traveling-wave tube because of the problem of circuit heating due to electron interception. Above this level of power, therefore, we must consider either a multiplicity of solid beams of preferably a large hollow beam. Despite the increased interest in high power, and therefore in hollow beams, there appears to have been relatively little work done on the design of electron guns which are suitable for generating high-density, hollow electron beams, at least in comparison with the effort which has been expended in research and development of guns for solid beams.