Studies on secondary electron yield and multipactor mitigation in rectangular waveguides based on Monte Carlo methods



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Mitigation of multipactor in waveguides is of great importance, and strategies have included the addition of external fields, materials engineering, or surface modifications to reduce the secondary electron yield (SEY), which is the underlying mechanism of multipactor. Both the SEY and multipactor are investigated in this study. Secondary electron emission from copper is probed utilizing Monte Carlo simulations that take account of elastic scattering based on the Mott theory, and inelastic collisions based on energy-dependent energy loss functions. The loss function and stopping power were obtained through first-principles Density Functional Theory. Angular assignment of electrons following elastic scattering, or the creation of secondaries is shown to affect the energy-dependent secondary electron yield (SEY). A good match of the simulation results (with a peak SEY of ~180% at around 300 eV, and less than 10% deviation over the 0 to 1000 eV energy range) to available experimental data is shown based on an energy and momentum conservation scheme. Geometry modifications of rectangular waveguide surfaces and application of an axial magnetic field are investigated for multipactor suppression. A Monte Carlo approach has been used to simulate electron dynamics. The empirical secondary electrons yield (SEY) is modeled based on a modified Vaughan approach. The electric fields driving electron transport were derived from separate, electromagnetic calculations to adequately include field perturbations due to the presence of surface patterns in the rectangular waveguide structure. Combinations of grooves and a DC magnetic field are shown to effectively mitigate multipactor growth at field strengths up to ~105 V/m. Finding optimal combinations for an arbitrary field and operating frequency requires further work.

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Secondary electron yield (SEY), Multipactor, Monte Carlo, Mitigation