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An 0.22 THz sheet beam TWT amplifier is under development in the DARPA HiFIVE program. In our prior work, FDTD-PIC simulation predicted that the plasmonic band circuit of a staggered double grating array produces 150 to 275 W, corresponding to 3-5.5% efficiency, at 0.22 THz over ~30% bandwidth with greater than 12 dB/cm growth rate, assuming a beam power of 5 kW. Subsequent Ka-band dispersion and attenuation measurements for proof-of-concept have shown excellent agreement with both a theoretical model and simulation analysis, showing a 25% active bandwidth and 0.15 dB/cm attenuation. A scandate nano-powder (Sc2O3-W) cathode developed at UCD has successfully demonstrated 80 A/cm2 space charge limited emission current at 1150degC and currently it is planned to incorporate it in the electron gun and PCM magnet design. The 0.22 THz circuit has been fabricated by both UV LIGA and high precision CNC machining with ~2-3 mum dimensional tolerance and ~50-100 nm surface roughness and its cold-test setup has been completed. The MEMS-fabricated THz plasmonic wave circuit will be tested for its dispersion and attenuation measurement.