Effects of oxygen on the formation of rabbit-like PD pattern in a void between metal surfaces

In a void between two metal surfaces, the φ-q-n pattern usually shows a band-like shape, but a quasi-rabbit-like shape often appeared for some time. After the voltage was applied for an hour, we opened the void to the air, and then re-applied the voltage on the sample. The transition from band-like to rabbit-like then to bandlike patterns was observed again. This suggests that the transition of the PD pattern may be due to the change of gas content in the void. By reducing the oxygen content in the void, the rabbit-like pattern became to appear earlier. This indicates the formation of the rabbit-like pattern is due to the oxygen content. These results may be useful in disclosing the mechanism of PD pattern transition in a usual void