This thesis examines novel Vacuum Electronic Devices (VEDs) and explores energy exchange between sub 30 keV electron beams and ElectroMagnetic (EM) waves. Beam-wave interaction is mediated via dispersion engineered artificial materials generating EM waves below 10 GHz. A low-loss artificial material was designed using concentric Complementary Split Ring Resonators (CSRRs) and the dispersion relation tailored to fit a specific set of requirements. Using effective medium theory and a Nicolson-Ross-Weir based constitutive parameter retrieval approach the EM characteristics of the artificial material were determined using Finite Element (FE) simulations. Finite-Difference Time-Domain (FDTD) Particle-In-Cell (PIC) simulations were used to investigate new device concepts. Several beam-wave interaction regimes were predicted, numerically verified, and experimentally validated. In this thesis two systems were considered, one comprising a rectangular waveguide loaded with four planar CSRR arrays, and a second comprising a novel cylindrical CSRR array loaded into a cylindrical waveguide. In the rectangular case, a 20 keV Direct Current (DC) beam was used to validate the predicted response producing a narrow-band signal at 8.46 GHz. FE eigenmode analysis of the rectangular system revealed a Transverse Magnetic (TM) mode similar to a TM14 mode around the predicted interaction frequency. In the cylindrical case, both 10 keV and 20 keV DC electron beams were used to experimentally validate the predicted response of the system. Measurements show the production of EM signals at 392.60 MHz and 1.76 GHz utilising 20 keV and 10 keV DC electron beams respectively. Numerical eigenmode analysis indicates the system supports a hybrid TM-like mode. The novelty of the results presented is the generation of a signal with a wavelength of 763.6 mm using a system 35 mm long and the frequency of the signal generated can be varied between 0.4 - 2.0 GHz by changing the beam voltage. This thesis presents theoretical, numerical, and experimental results that confirm that it is possible to mediate novel energy exchange from a low-energy DC electron beam to generate an EM wave using dispersion-engineered artificial materials. Results suggest that the conceptual VEDs presented can operate over a very large bandwidth (0.4 - 2.0 GHz for the cylindrical system), far greater than what is currently achievable with conventional VEDs. The potential power-handling capabilities of the novel VEDs presented was investigated, and results indicate that the artificial material could withstand relatively high power in a continuous mode of operation.
| Date of Award | 2 May 2024 |
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| Original language | English |
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| Supervisor | Rebecca Seviour (Main Supervisor) & Ian Glover (Co-Supervisor) |
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