The unwanted emission of secondary electrons from dielectric and metallic surfaces can pose a variety of experimental difficulties. Because of its ability to significantly change the electric potential profiles and fluxes near material surfaces, the phenomenon interferes with charge-based systems, like the defocusing of beams in particle accelerators. New simulations described in the Journal of Applied Physics explore how whiskered foam surfaces might be used to suppress the effective yield of secondary electrons.
Researchers at the Princeton Plasma Physics Laboratory modeled a foam surface with whiskers with an enhanced ability to trap secondary electrons. From Monte Carlo simulations, the authors found that foams were able to capture and significantly reduce the secondary electron yield isotropically, but might be less than ideal for applications in with a known direction of primary electrons.
Secondary electrons result from impacts of primary highly energetic electrons, UV, or X-ray photons. Previous research found that velvet, with its aligned fibers, was well-suited to trap these electrons when traveling in a single direction.
For this work, they simulated a fibrous graphite foam surface that formed a layer of randomly arranged fibers to trap secondary electrons from all directions. This simulated foam was able to reduce secondary electron emission by 70 percent.
The results show that foam-based surfaces would perform better with isotropic distribution than velvet, but would perform worse for certain well defined directions of incident primary electrons.They also help characterize foams that form with some high-temperature plasmas and determine the optimal material for different low-temperature plasma applications.
Source: “Modeling of reduced secondary electron emission yield from a foam or fuzz surface,” by Charles Swanson and Igor D. Kaganovich, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5008261.
