SURVEY OF PULSE SHORTENING IN HIGH-POWER MICROWAVE SOURCES

Observations show that the ubiquitous pulse shortening in high-power m icrowave (HPM) devices arises from the formation of plasma, electron s treaming, high-E-field breakdown, and beam disruption. We review recen t experiments in terms of these causes, Linear beam devices exhibit al l of these mechanisms; in particular, beam disruption by E x B drifts in the strong microwave fields and diffusion in turbulent electric fie lds appear common, In relativistic magnetrons, the dominant effect is resonance destruction by cathode plasma motion, possibly from water co ntamination of the surface, Wall plasma effects shorten pulses inmost sources. We call for the introduction of improved surface conditioning , cathodes which do not produce plasmas, and increased effort on the m easurements of the high-field and plasma properties of HPM sources. Be cause of the broad nature of the phenomena in pulse shortening, we app eal for increased participation of the plasma, intense particle beam, and traditional microwave tube communities in pulse-shortening researc h.