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P: Fachverband Plasmaphysik

P 14: Plasma Wall Interaction II / HEPP III

P 14.2: Vortrag

Mittwoch, 30. März 2022, 16:15–16:30, P-H12

Secondary electron emission from metals at low impact energies — •Franz Xaver Bronold and Holger Fehske — Institut für Physik, Universität Greifswald, 17489 Greifswald, Germany

The interaction of electrons with the walls of discharges is an important surface process in low-temperature plasmas. It affects, for instance, the operation modii of barrier discharges, Hall thrusters, and divertor plasmas in fusion devices. Little is known quantitatively about the process because it typically occurs at energies below 50  eV which are hard to access experimentally. There are thus only a few attempts to measure secondary emission yields in this energy range. A few years ago, we presented therefore an approach, based on an embedding principle, for calculating the complement of the emission yield, the absorption probability, from a microscopic model and applied it to dielectric walls at impact energies below the band gap, where backscattering due to electron-electron collisions is absent. We now generalized the approach to account for it. In addition, we developed a scheme to solve numerically the full nonlinear embedding equation (not only its linearized version), and included–depending on the crystallinity of the surface–Bragg gaps due to coherent scattering on the crystal planes parallel to the interface or incoherent scattering on the ion cores of the bulk. Applying this approach to metal surfaces, we find for impact energies up to 20 eV good agreement with measured emission yields. Depending on the metal and surface quality, the yields are around 10-30 %. Hence, even metal surfaces turn out to be not perfect absorber for electrons.