Novel HPM source topologies for high power microwave and millimeter wave generation
Abstract
APPROVED FOR PUBLIC RELEASETraditional high power microwave (HPM) vacuum electronic devices (VEDs) tend to follow a power-frequencyscaling relation, such as Pf = const. or Pf2 = const. (where P is the power of the HPM source, and f is the HPM frequency). These scaling relations lead to serious challenges for the realization of VED sources at higher frequencies (X-band and above) with power levels approaching 1 GW. In an effort to realize a simple VED, free of these scaling relations, this study will experimentally explore and characterize the operational space of a novel VED topology, a triaxial split cavity oscillator (TSCO).As was previously observed in relativistic klystron studies, the utilization of a triaxial configuration is anticipated to allow for significantly larger device dimensions for a given frequency, thus allowing for higher total beam current and ultimately higher achievable output power. Toovercome issues associated with grid outgassing and damage, characteristic to previous split cavity oscillators, this work will employ thin layers of pyrolytic graphite (and similar novel materials) to serve as the electron transparent, electrically conductive grid in the split cavity assembly. While earlier works have demonstrated the successful application of thin layers of pyrolytic graphite as an electron transparent media in high power vircators, prior studies have not demonstrated the ability of pyrolytic graphite to pass a high energy electron beam while also supporting the surface currents necessary to establish a resonant electromagnetic modein a cavity.Year 1 of the proposed research will include theoretical modeling and particle-in-cell simulation of TSCOs over a wide parameter space, before completing the in-depth design of an X-band device. Year 1 will also include the design and fabrication of anovel, moderate time-averaged power, square pulse marx generator experimental test stand. Year 2 of this effort will include the fabrication and experimental test of the X-band (10 GHz) TSCO, beginning with the characterization of single-pulse HPM performance (output power, frequency, radiation pattern, etc.). This will be followed by the experimental test of HPM performance at moderate time-averaged power (~few Hz pulse repetition rate and ~few kW of time-averaged power), again focusing primarily on HPM performance. Thiswill be followed by the design of a K-band TSCO (18 GHz), while additional experiments on the X-band TSCO will include residual gasanalyzer measurements and SEM characterization of cathode and anode materials. Year 3 of this effort will continue experiments on the X-band TSCO to include optical emission spectroscopy measurements of plasmas generated at the beam-grid interface and laser beam deflection measurements of absolute gas density. As in year 2, in year 3, experiments on the K-band TSCO will begin with single-pulse characterization followed by moderate time-averaged power testing. Again, experiments will continue on the K-band TSCO to include residual gas analyzer measurements, optical emission spectroscopy measurements, and laser deflection measurements. During this same period, utilizing theoretical models and the particle-in-cell model validated by experimental data collected in this effort, the design of a Ka-band TSCO will be completed.In total, this research would be a new look at a novel version of a classical VED topology that has historically received only limited attention. By exploiting advances in modern materials capability, and the reconfigurationof the device to a triaxial structure, this approach aims to realize a low-complexity VED for the production of HPMs at frequenciesranging X-band to K-band. By testing the proposed device at both X-band and K-band, far above the traditional frequency range of traditional split cavity oscillators, this study will provide critical insight regarding the power-frequency performance characteristics of this new VED topology.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 12, 2023
- Source ID
- N000142312305
Entities
People
- Jacob C Stephens
Organizations
- Office of Naval Research
- Texas Tech University System
- United States Navy