Large-scale parallel numerical simulations of the relativistic klystron oscillator

Summary form only given, as follows. The Phillips Laboratory has a strong research effort in the development of high-power microwave devices. One device of interest to the experimental program is the relativistic klystron oscillator (RKO). Previous numerical simulations of the device predict extracted powers well above those observed experimentally. This discrepancy may be caused by insufficient resolution or overly truncated problem domain due to computational resource restraints or by neglect of the physical phenomena responsible for the power loss. To overcome the obstacle of limiter computational resources, we have developed a 3D parallel particle-in-cell (PIC) code specifically designed to model microwave tubes. We discuss the design issues and implementation techniques specific to parallel codes, and describe our own parallelization, partitioning, and dynamic re-load balancing schemes. A brief overview of the code is given and timing results are presented. The benefits of dynamic load migration are also discussed. To better address phenomena suspected to be responsible for power loss but missing from the basic PIC model, we have implemented a Monte Carlo collisional (MCC) treatment in our code. Large-scale simulations of the RKO are presented both with and without collisional effects. Results from both of these simulations are compared to experimental data, and the necessity of including collisional effects is assessed.