Influence of μm-level profile slopes on vacuum DC flashover: a model guided design optimization

Surface microstructures (<1 mm) have important influences on the surface insulation strength of insulating materials, which are typically quantified by surface roughness. However, conventional roughness parameters, such as the arithmetic mean height of profile (R_a), cannot distinguish complex microstructures, potentially resulting in different insulation performances of materials with the same roughness. This study proposes a parameter, the sum of unit-length profile slopes (denoted as R_k), which is suitable for characterizing the surface roughness, especially the surface with a structure of regular grooves. Alumina ceramic samples with the same R_a and different R_k are obtained by laser surface grooving, and the effect of R_k on surface insulation performance is studied systematically. It is found that as R_k increased, the surface conductivity showed an upward trend, the surface potential decay of the samples accelerated, the secondary electron yield decreased, and the vacuum flashover voltage increased. Properly adjusting R_k can effectively enhance the strength of the surface insulation of alumina ceramic. The combination of R_a and R_k can serve as a useful tool for the design of surface structures on insulating materials.