  In the development of high efficiency and high gradient RF-accelerators, RF
waveguides and cavities have been designed with Photonic Band Gap (PBG) and
fishnet- metamaterial structures. The designed structures are comprised of a
periodically corrugated channel sandwiched between two photonic crystal slabs
with alternating high to low dielectric constants and a multi-cell
cavity-resonator designed with fishnet-metamaterial apertures. The structural
designs of our interest are intended to only allow an operating-mode or -band
within a narrow frequency range to propagate. The simulation analysis shows
that trapped non-PBG modes are effectively suppressed down to ~ -14.3 dB/cm,
while PBG modes propagated with ~2 dB of insertion loss, corresponding to ~1.14
dB/cm attenuation. The pre- liminary modeling analysis on the fishnet-embedded
cavity shows noticeable improvement of Q-factor and field gradient of the
operating mode (TM010) compared to those of typical pillbox- or PBG-cavities.
Fabrication of the Ka-band PBG-waveguide and S-band fishnet cavity structures
is currently underway and they will be tested with a microwave test bench/8510C
Network Analyzer and 5.5 MW S-band klystron. These structures can be applied to
stable short-bunch formation and mono chromatic radiation in high frequency
accelerators.
