Novel RF waveguides comprised of composite metamaterials with photonic crystal (PC) slabs have been investigated for terahertz (THz) sheet beam device applications such as high gradient accelerators and coherent radiation power sources. Field and dispersion-relation analyses based on numerical EM simulations showed that the designed dielectric PC slabs filter highly overmoded fundamental passband of a sheet beam plasmonic wave structure (staggered grating pair) within a narrow dynamic frequency range of beam-wave synchronism, capable of avoiding various instabilities such as cutoff- and spurious oscillations. Further investigation on the photonic-band-gap (PBG) effect was also extended to the negative index metamaterial (NIM) of split-ring-resonator (SRR) and wire arrays (wire-SRR). It appears that in the composite waveguide a backward plasmonic wave is superimposed with a forward propagating wave, enhancing field intensity at electric and magnetic resonant frequencies. Currently, a beam-wave interaction is being considered with full 3D particle-in-cell (PIC) simulations and RF-test system construction for proof-of-principle (POP) is under way.
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