CONTRIBUTIONS TO RESOLVING ISSUES IMPEDING THE OPERATION OF HIGH POWER MICROWAVE AND SUBMILLIMETER DEVICES

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dc.contributor.advisorGranatstein, Victor L.en_US
dc.contributor.advisorNusinovich, Gregory S.en_US
dc.contributor.authorKashyn, Dmytroen_US
dc.contributor.departmentElectrical Engineeringen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2014-10-16T05:37:18Z
dc.date.available2014-10-16T05:37:18Z
dc.date.issued2014en_US
dc.description.abstractThis thesis reports an experimental study aimed at extending high power, high efficiency gyrotron operation to submillimeter wavelengths. A series of experiments carried out both at the University of Maryland and the Institute of Applied Physics of the Russian Academy of Science, succeeded in demonstrating output power at 670 GHz of 180 kilowatts with 20% efficiency (gyrotron voltage was 57 kV and beam current was 16 amperes). The maximum output power achieved in the experiments was 210kW at somewhat higher voltage and current (viz. 58kV and 22A). The achieved output power and efficiency are twice as large as achieved in previous experiments in this frequency range with pulse duration in the range of tens of microseconds. These performance parameters are relevant to a previously proposed application of detecting concealed radioactive materials by air breakdown in a focused beam of sub-millimeter radiation. The 670 GHz gyrotron combined features of two lines of previous experiments: (a) to operate at the required frequency, pulsed solenoids producing 28T magnetic were employed and (b) to obtain high efficiency a very high order mode was used in the gyrotron cavity, as in the experiments with gyrotrons for plasma heating. Evidence of multimode beating was observed in submillimeter output envelope. The excitation of spurious modes, especially during the rise of the gyrotron voltage pulse, was analyzed and the method of avoiding this was proposed which also allows to reduce collector loading in gyrotrons operating in modulated regimes. The present study also includes theoretical analysis of the processes that deepens the understanding of microwave breakdown (arcing) in high power microwave devices. The effect of the dust particles microprotrusions on the device operation was analyzed. These microprotrusions were observed and their negative effects were remedied by careful polishing and machining of the resonator surface. Finally, the generated 670 GHz radiation was focused and used to study breakdown both in argon and in the air. This breakdown volume was theoretically analyzed and the effects of the atmospheric turbulence on the air breakdown were included.en_US
dc.identifierhttps://doi.org/10.13016/M29026
dc.identifier.urihttp://hdl.handle.net/1903/15902
dc.language.isoenen_US
dc.subject.pqcontrolledElectrical engineeringen_US
dc.subject.pqcontrolledElectromagneticsen_US
dc.subject.pquncontrolleddark currenten_US
dc.subject.pquncontrolledgyrotronen_US
dc.subject.pquncontrolledmicroparticlesen_US
dc.subject.pquncontrolledpulsed magneten_US
dc.subject.pquncontrolledradiationen_US
dc.subject.pquncontrolledterahertzen_US
dc.titleCONTRIBUTIONS TO RESOLVING ISSUES IMPEDING THE OPERATION OF HIGH POWER MICROWAVE AND SUBMILLIMETER DEVICESen_US
dc.typeDissertationen_US

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