INFLUENCE OF SURFACE-ROUGHNESS ON SECONDARY-ELECTRON EMISSION AND ELECTRON BACKSCATTERING FROM METAL-SURFACE

Because of its acute importance in the understanding of low-energy (less than or equal to 1 keV) electron-material interactions in thermonuclear fusion devices, the effect of surface roughness on the secondary electron yield and backscattering coefficient, as well as on the energy and angular distributions of emitted electrons, is investigated using a Monte Carlo simulation combined with a model of ripple structure for the roughness. Two different effects of surface roughness are demonstrated. One is that low-energy and obliquely oriented electrons, which cannot escape from a flat surface, can escape from an inclined plane of the rough surface. The other is that electrons emitted near the bottom of the rough area re-enter into the surface. The former effect, which is dominant for small roughness, causes an increase in the secondary electron yield and an increase of the low-energy component in the energy distribution. The latter effect, which is dominant for large roughness, causes a decrease in the secondary electron yield and backscattering coefficient, as well as angular distributions of the over-cosine type.