Development of a 10-kW W-band sheet beam extended interaction klystron (EIK)

Summary form only given. A W-band extended interaction klystron (EIK) driven by a 19.5-kV, 3.5-A sheet beam is being developed. Simulations using the 3-D particle-in-cell codes MAGIC and ICEPIC predict saturated output power levels of 8-10 kW with a saturated gain >;30 dB and small signal gain >;40 dB. A beamstick has been successfully fabricated and tested, transporting 98% of the emitted current through a 0.4-mm x 5-mm x 20-mm-long beam tunnel.3 Performance of the beamstick was in excellent agreement with MICHELLE simulations. We will focus here on critical design issues related to the EIK circuit and its fabrication. The circuit consists of three 5-gap cavities operated in the 2π mode. The gap dimensions and period are optimized for beam-wave interaction. The dimensions of the coupling cavities that connect the gaps and the irises that couple the cavities to standard WR-10 rectangular waveguides strongly impact the field uniformity within the gaps and the interaction impedance. Because sheet-beam EIK cavities are intrinsically over-moded, a design that provides maximum mode separation is critical. Examples of techniques to address these issues will be presented. The 5-gap cavities have relatively high R/Q values -50 Ω, so care has to be taken to avoid oscillation when small perturbations are introduced (e.g., beam and/or beam tunnel displacement relative to the cavity structure, cavity fabrication errors, etc.). Simulations illustrating the sensitivity to such perturbations and methods for limiting their impact will be described. A two-cavity circuit has been fabricated and cold tested, and its performance agrees extremely well with ANALYST electromagnetic simulations. Fabrication of the complete amplifier is in progress, and the status will be presented.