Three-dimensional particle-in-cell calculations of an over-moded W-band gyrotron

Summary form only given. Standard gyrotron design tools are likely to be taxed to the limits of their utility when pressed into service for the next generation gyrotron required by the Air Force. Alternative and complementary approaches may help to increase the efficacy of the overall modeling and design effort. One such alternative is the electromagnetic particle-in-cell (PIC) code. The gyrotron presents a considerable challenge to the PIC approach due to its high frequency (in the neighborhood of 100 GHz), its disparate spatial scales (ranging from the beam width and electromagnetic wavelength to the scalelength of the device), the time required to reach saturated behavior (tens of thousands of periods), and its inherently three-dimensional nature. Thus, at the outset, it was far from certain that the PIC approach could make headway in modeling the gyrotron. Our initial demonstration is now coming to completion, wherein ICEPIC, the Air Force Research Laboratories´ three-dimensional, electromagnetic, parallel PIC code, has been used to perform calculations based on AFRL´s 100 kW-class gyrotron. These calculations have investigated the influence on performance of various design variables, such as tube geometry and applied magnetic field strength. A single particle tool has been used to guide these calculations. The single particle tool provides beam energy extraction predictions for given gyrotron parameters. Comparisons between these predictions and ICEPIC results have helped us to create ICEPIC calculations that predict tube performance that is consistent with that observed in the laboratory. Details of these calculations were discussed along with how this approach can fit into the standard gyrotron design strategy.