Investigations of a Double-Gap Vircator at Submicrosecond Pulse Durations

The results of investigations of a double-gap vircator driven by a 20 Ω and 500-ns generator operating in the output voltage range 400-600 kV are presented. The vircator generated microwave pulses with a peak power of up to 200 MW at ~5% efficiency and the frequency varied from 2.0 to 2.3 GHz depend...

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Bibliographic Details
Published in:IEEE transactions on plasma science 2012-06, Vol.40 (6), p.1607-1617
Main Authors: Shlapakovski, A. S., Queller, T., Bliokh, Y. P., Krasik, Y. E.
Format: Article
Language:English
Subjects:
Acceleration
Cathodes
Cavity resonators
Delay
Electrodes
Electrons
Generators
Geometry
High-power microwaves
Microwave generation
microwave pulse shortening
Oscillators
Plasma physics
Plasmas
Radio frequency
vircators
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Summary:The results of investigations of a double-gap vircator driven by a 20 Ω and 500-ns generator operating in the output voltage range 400-600 kV are presented. The vircator generated microwave pulses with a peak power of up to 200 MW at ~5% efficiency and the frequency varied from 2.0 to 2.3 GHz depending on the cavity geometry. The limitations on the microwave pulse duration not related to the cathode plasma expansion are addressed. On the one hand, the microwave generation is terminated because of the plasma formation at the foil separating the cavity sections, so that the virtual cathode (VC) electron space charge is neutralized by the plasma ion flux. On the other hand, if the electron beam energy deposition into the foil is reduced, a substantial delay in the start time of the microwave generation appears, which has been studied in detail. With these limiting factors, the microwave pulse full duration varied from 100 to 350 ns; the maximal full width at half maximum duration achieved in the experiments was ~180 ns. Measurements of the current transmitted through the vircator cavity indicated the existence of a VC in spite of the absence of microwave generation during the delay. The experimental dependence of the microwave generation starting current on the diode voltage is presented, and possible mechanisms behind the generation delay are discussed. Simplified numerical simulations emphasize the role of the portion of electrons that are reflected from the VC, the number of which must be sufficient for the microwave generation to occur.
ISSN:0093-3813
1939-9375
DOI:10.1109/TPS.2012.2190104