Design Of A 250 GHZ Photonic Bandgap Extended Interaction Klystron

Production of millimeter wave and near-THz vacuum electron devices is largely limited by the ability to fabricate very small features on the order of tens of micrometers with near micrometer tolerances. This study details the development of a 250 GHz extended interaction klystron (EIK) amplifier design with uncharacteristically large features. The EIK operates at 30 kV with a beam current of 0.3 A. The interaction cavities operate in the $2 \pi -$mode such that their physical period is $389 \mu \mathrm {m}$. The EIK design utilizes an oversized beam tunnel diameter of $300 \mu \mathrm {m}$. Consequently, lower magnetic field is required to confine the beam at a given current. Most importantly, the EIK input and output cavities feature a modified photonic bandgap (PBG) scheme to achieve the optimum coupling coefficient. Ultimately, the $100 \mu \mathrm {m}$ diameter holes for PBG rods are the smallest dimension needed for fabrication of the EIK, whereas more conventional coupling schemes require features on the order of $30 \mu \mathrm {m}$ at these frequencies.