Novel Concepts for Slow Wave Structures used in High Power Backward Wave Oscillators
Advisor:Volakis, John L.
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Series/Report no.:2017 Edward F. Hayes Graduate Research Forum. 31st
This proposal presents novel slow wave structure (SWS) designs and concepts that have been developed to significantly improve the efficiency and performance of high power backward wave oscillators (BWOs). A novel slow wave structure design is presented. The design features a deeply corrugated cylindrical waveguide with cavity recessions and metallic ring insertions. A new technique for mode control in waveguides is also presented. In addition to demonstrating mode control in slow wave structures, the key aspects of the presented design are mode dominance reversal and a 100% improvement in interaction impedance. A novel and cost efficient fabrication technique for the SWS is presented. Fabrication and testing results are also presented to experimentally validate the dispersion properties of the novel SWS. Furthermore, we experimentally demonstrate, for the first time, mode dominance reversal in SWSs. We extend the concepts of inhomogeneous SWSs by designing a 3-section inhomogeneous SWS to further enhance the BWO energy conversion efficiency. Results from commercial particle in cell codes predict an output power of 5.92 MW at 27 GHz with 58% peak power efficiency. Further S band simulations using the concepts outlined above predict 8.25 MW output power at 2.62 GHz with 70% peak power efficiency. These results must be compared to the 20-25% peak power efficiency associated with conventional slow wave structure designs. Future work will be focused on designing and fabricating a full SWS and coupler for a hot test experiment at the M.I.T Plasma Science and Fusion Center. Multi-section (more than 3 sections) inhomogeneous SWS behavior will be investigated and characterized in regards to BWO efficiency enhancement. New methods of efficiently operating BWOs under low magnetic field conditions will also be investigated. High frequency SWS design solutions for high efficiency operation will be investigated.
Engineering: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)