RF amplifier design using 3D EM-PIC

Summary form only given. The 3D Electromagnetic Particle-in-Cell (EM-PIC) algorithm provides a powerful method to predict performance of RF amplifiers based on actual device geometry and defined operating parameters. Until recently its utility as a primary design tool has been restricted by long simulation times or limited accuracy, due to computational and/or algorithmic constraints of available implementations. Advances in the representation of geometry using conformal techniques, coupled with highly parallel implementations of the EM-PIC algorithm, have made EM-PIC viable as a primary design tool. The EM-PIC code Neptune^{1, 2} exploits highly parallel GPU hardware in conjunction with conformal geometry representation to perform fast, accurate amplifier simulations. It is now a primary tool at NRL for the design and simulation of single- and multi-stage TWT amplifiers (serpentine waveguide, folded waveguide, helix, transverse TWT), klystrons and EIK amplifiers, and has enabled new research into advanced device concepts including cascaded multi-beam TWTs and transverse-interaction TWT amplifiers. We report on recent additions to Neptune´s algorithms that directly support the needs of RF amplifier design. First, a new method to improve the discretization accuracy for dielectric regions will be demonstrated, based on a novel subcell averaging scheme. Second, we report on a range of new features supporting device design. New particle beam and magnetic field import facilities allow interfacing with complementary design tools, including the gun/collector code MICHELLE3, while new diagnostics for RF current and beam interception allow detailed monitoring of device operation.