Vacuum breakdown strength of vacuum-degassed oxygen-free copper electrodes

Using an in situ electrode surface cleaning system, the vacuum breakdown strength of vacuum degassed oxygen free copper (VDOFC) electrodes satisfying ASTM-F-68 Class 1, 3, and 5 purity specifications was measured. Breakdown experiments reveal that the breakdown field (breakdown voltage/gap length) depends on the purity of the VDOFC electrodes. The initial breakdown strengths are 1.96×10⁷ V/m for Class 1 copper, 1.89×10⁷ V/m for Class 3, and 1.85×10⁷ V/m for Class 5. After 500 breakdowns, these figures were improved to 18.3×10⁷ V/m for Class 1, 17.5×10⁷ V/m for Class 3, and 11.8×10⁷ V/m for Class 5. It is concluded that the gas content in the electrodes is an important factor relating to the vacuum breakdown strength, provided the electrode surface is properly cleaned