3-D simulation of klystrons

Summary form only given, as follows. The last couple years have seen a large increase in the use of 3-D electromagnetic-PIC simulation. Klystrons are typically some of the most difficult vacuum electron devices to model in electromagnetic PIC, because of the close tolerances on geometry, bandwidth, and power loading, and because of the inherently long run times in terms of RF cycles. The need for 3-D modeling, rather than 2-D, is driven by inherently 3-D devices such as multiple beam klystrons, sheet beam klystrons, and relativistic annular beam klystrons. However, there is also interest in modeling the 3-D output coupling geometry in conventional round-beam klystrons, especially when multiple cavity output circuits are employed. Several new modeling capabilities have been developed to facilitate the 3-D simulation of klystrons, in addition to the continual upward march of CPU speed. These include a 3-D resonant-port model capable of proper handling of space-charge, and progress on finite-element type metal boundary conditions. The former can dramatically reduce the cavity fill time, while the latter can help ease the demand for small cell size, since it provides accurate modeling of curved surfaces with moderate resolution. Also, the realistic modeling of periodic permanent magnet focusing in 3-D is also now commonplace. The application of these new modeling capabilities will be illustrated for the devices listed above.