UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Author: search.filters.author.Larsen, Paul BenjaminSubject: search.filters.subject.instabilities

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    Design of an Overmoded Ka-Band Sheet-Beam Coupled-Cavity Traveling-Wave Tube Amplifier
    (2011) Larsen, Paul Benjamin; Antonsen, Thomas M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis develops a qualified design for a sheet-beam coupled-cavity slow-wave structure for use in a high-power millimeter wave traveling wave tube amplifier. The main advance realized in the design is the roughly ten-fold increase in power gained by utilizing a sheet, rather than cylindrical, beam while at the same time employing mode-suppression techniques to suppress competing modes that are introduced by the sheet geometry. This design addresses considerations relevant to high-power tubes in general, as well as points specific to the design of a sheet-beam structure. The coupled-cavity structure is designed with the following general characteristics: center frequency of 35 GHz with greater than a 10% bandwidth, and capabilities of 5 kW pulsed output power. The device operating parameters are as follows: a moderate gain of 18 dB, and an experimentally demonstrated sheet electron beam with 3.5 A, 19.5 kV, and 0.3 mm x 4.0 mm beam cross-section. The final design goal has been to limit the interaction length as much as possible to reduce magnet weight and complications. A final design structure is proposed, which produces in excess of 5 kW peak power in simulation with safeguards from instabilities. The structure geometry is based on a novel design for a sheet-beam coupled-cavity slow-wave structure that has been characterized through various analyses, simulations, and experiments. This thesis outlines and details the various techniques used to probe the structure and thus form a full characterization of the structure and proposed amplifier device. The concept espoused by much of this work is to adapt the analyses from cylindrical beam devices for the sheet-beam geometry. Then we make comparisons between the new sheet-beam structure and conventional devices. From these comparisons we draw conclusions on the operation of sheet-beam amplifiers and make design choices accordingly. The final design is validated with fully three-dimensional particle simulations and predicts stable amplification across the range of operation.