Experiment on the vacuum breakdown of hard anodized aluminum electrode under pulsedvoltageof tens of nanoseconds

High breakdown field strength between metal grading rings and vacuum flares is of great benefit to obtain low inductance, high performance stack-MITL system for high current pulsed power facility. Experiments were done to explore the effects of the hard anodized aluminum coating on the breakdown field strength under pulsed voltage. The diameter of the test electrodes were 100 mm. With the gap distance of 4 mm, the breakdown field was $\sim 1.20 \mathrm{MV} / \mathrm{cm}$ for anodized aluminum electrodes with coating thickness of $3-40 \mu \mathrm{m}$, which was 140% higher than that of the mechanically polished aluminum without coating. Tests showed that the breakdown field was insensitive to to the hard anodized film thickness as it ranged from $3 \mu \mathrm{m}$ to $40 \mu \mathrm{m}$. Whereas, if there existed a crack in the film, which is hardly to avoid in the common industrial hard anodized alumina products, the gap breakdown field strength decreased from $1.20 \mathrm{MV} / \mathrm{cm}$ to $0.73 \mathrm{MV} / \mathrm{cm}$. The roughness of the electrode base significantly influenced the breakdown field strength. As the roughness increases from Ra $1.4 \mu \mathrm{m}$ to $2.7 \mu \mathrm{m}$, the breakdown field strength decreases from 1.48 $\mathrm{MV} / \mathrm{cm}$ to $0.93 \mathrm{MV} / \mathrm{cm}$.