Insepov, Z.Norem, J.Proslier, T.Huang, D.Mahalingam, S.Veitzer, S.2017-09-272017-09-272010Insepov, Z., Norem, J., Proslier, T., Huang, D., Mahalingam, S., & Veitzer, S. (2010). Modeling RF breakdown arcs. arXiv preprint arXiv:1003.1736.http://nur.nu.edu.kz/handle/123456789/2726We describe breakdown in 805 MHz rf accelerator cavities in terms of a number of self-consistent mechanisms. We divide the breakdown process into three stages: (1) we model surface failure using molecular dynamics of fracture caused by electrostatic tensile stress, (2) we model the ionization of neutrals responsible for plasma initiation and plasma growth using a particle-in-cell code, and (3) we model surface damage by assuming a process similar to unipolar arcing. We nd that the cold, dense plasma in contact with the surface produces very small Debye lengths and very high electric fields over a large area, consistent with unipolar arc behavior, although unipolar arcs are strictly de ned with equipotential boundaries. These high elds produce strong erosion mechanisms, primarily self-sputtering, compatible with the crater formation that we see. We use the OOPIC model to estimate very high surface electric elds in the dense plasma and measure these elds using electrohydrodynamic arguments to relate the dimensions of surface damage with the applied electric eld. We also present a geometrical explanation of the large enhancement factors of field emitters.This is consistent with the apparent absence of whiskers on surfaces exposed to high elds. The enhancement factors we derive, when combined with Fowler-Nordheim analysis, produce a consistent picture of breakdown and eld emission from surfaces at local elds of 7{10 GV/m. We show that the plasma growth rates we obtain from OOPIC are consistent with growth rates of the cavity shorting currents using x-ray measurements. We believe the general picture presented here for rf breakdown arcs should be directly applicable to a larger class of vacuum arcs. Results from the plasma simulation are included as a guide to experimental veri cation of this model.enOpen Access - the content is available to the general publicAttribution-NonCommercial-ShareAlike 3.0 United Statesrfrf breakdownvacuum arcArticle