Analysis Of Experimental Multipactor Observation Signals Using Spark3D Software

Multipactor is a resonant nonlinear electron multiplication effect that may occur in high power microwave devices at very low pressures, such as those operating in particle accelerators and satellite subsystems. Its effects range from signal degradation to the damage and destruction of microwave components. Thus, multipactor physics has been studied through theoretical analysis, numerical simulation, and experiment. Previously, we developed a direct electron observation system using an Electron Multiplier Tube (EMT) and succeeded to directly detect multipactoring electrons in the center of the broadwall of rectangular waveguides
^{1, 2}
. Here, we provide a method for evaluating the electric charge density and secondary emission yield (SEY) in waveguides. The experimentally obtained EMT signal is analyzed with the extensive usage of the numerical simulation software Spark3D. The software was utilized to analyze multipactor onset in waveguide structures, where the electric field distribution without multipactor was carefully simulated, employing high-frequency solvers. The EMT signal and the charge density were simulated for the same conditions as the experiment. As a result, a calibration line indicating the proportional relation between the EMT voltage and the charge density, which is independent of some conditions, i.e., input power and gap size, was obtained. Further, after adjusting the SEY curve imported to Spark3D, the rising shape of the experimental EMT signal pulses fit with the simulated one, and the experimental threshold power for the EMT signal generation was consistent with the simulated multipactor threshold power. Since the simulation matches the experiment in threshold power and signal shape, one expects that the charge density and SEY curve deduced from the simulation are accurate.