3.5: Sheet beam EIK sensitivity to multimoding and circuit imperfections

A sheet-beam Extended Interaction Klystron (EIK) is an attractive MMW amplifier because of its enhanced power capability, compactness, and relatively high gain per unit length. However, an intrinsic problem with a sheet beam amplifier is its susceptibility to multimoding, which results because the width of the device is typically larger than a wavelength. Even in its ideal configuration, a sheet beam slow wave structure can support a number of closely spaced modes. Furthermore, small imperfections or asymmetries can excite a fundamental TE₁₀ mode in the rectangular beam tunnel, which can cause oscillation or otherwise degrade performance. We have performed 3D PIC simulations (using MAGIC and ICEPIC) to study these effects in several different EIK structures. We will describe methods for minimizing the deleterious effects of multimoding and imperfections, present results of the simulations, and compare the two PIC codes.