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Proceedings Paper

Progress toward steady-state high-efficiency vircators
Author(s): Peter Poulsen; Phillip A. Pincosy; Jasper Jim Morrison
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Paper Abstract

The resonance at which high-efficiency operation of virtual cathode oscillators is obtained occurs when the beam frequency equals the reflex frequency to within 2%. This tolerance limit in the frequency ratio implies that cathode closure in the anode-cathode gap is not acceptable. The authors have developed and tested a 6-cm2 cathode that will operate longer than 1 microsecond(s) at 300 A/cm2 without significant closure. As yet, the full-scale (>80 cm2) cathode has not worked quite as well. In many tests, the cathode will operate in the emission-limited temperature/field (T/F) mode for approximately 300 ns, and then transition into explosive emission with a relatively slow ($OM0.5 cm/microsecond(s) ) closure rate. The current density was 45 to 90 A/cm2. High-power rf-emission tests have not been run under conditions where the diode stays open and in resonance for the duration of the rf pulse at a current density of 250 A/cm2, which is required for 3-GHz operation; that test remains the focus of continuing research. Long (600-ns) duration rf pulses have been obtained at low power. The data base on microwave generation at lower power also has been extended and has shown that high-efficiency resonances will occur when a multiple of the reflex frequency equals the beam frequency. This allows greater flexibility in the design and scaling of microwave device.

Paper Details

Date Published: 1 April 1991
PDF: 11 pages
Proc. SPIE 1407, Intense Microwave and Particle Beams II, (1 April 1991); doi: 10.1117/12.43493
Show Author Affiliations
Peter Poulsen, Lawrence Livermore National Lab. (United States)
Phillip A. Pincosy, Lawrence Livermore National Lab. (United States)
Jasper Jim Morrison, Lawrence Livermore National Lab. (United States)

Published in SPIE Proceedings Vol. 1407:
Intense Microwave and Particle Beams II
Howard E. Brandt, Editor(s)

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