Improved Emission/Ionization Algorithms and Modeling Methodology for Design of High-Brightness Electron Guns

High-brightness electron beams are needed for improved power production and reliability of microwave tubes operating in the 80GHz - 300GHz range. At these frequencies, the beam size becomes sufficiently small that beam emittance begins to play a more significant role in the beam dynamics, intensifying thermal management issues and efficiency constraints. To properly model beam formation off the cathode, the intrinsic emittance of the emission due to effects such as material preparation and surface finishing, must be captured in new models. Secondary generation on gun surfaces, particularly on intercepting grids, can lead to thermal tails on the beam and beam halos. Moreover, impact ionization of background gas can enhance beam halos and lead to cathode erosion or poisoning over time, thereby limiting emission life. We propose to develop validated, improved secondary emission and ionization algorithms within the MICHELLE code for modeling high-brightness beam generation, acceleration, and transport. Specifically, these models will capture the non-ideal effects that could lead to beam brightness degradation in electron beam sources commonly used in millimeter-wave tubes. Support for user-control of the new algorithms will be implemented within the MICHELLE interface module in the Analyst finite-element package. Specializations of the Analyst adaptive mesh refinement and optimization functionality will also be developed to improve the capability to design high-brightness guns.