The effect of alumina inclusions on the breakdown and emission properties of copper surfaces in vacuum

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Abstract
We have studied electrical breakdown in vacuum for copper electrodes which have been intentionally contaminated by adding 1/2% by weight of alumina powder having a size of 500, 50, or 5 μm. Electron emission, pulse breakdown, and scanning electron microscopy have been used to evaluate the dielectric characteristics of the surfaces. Comparison of these results with those obtained using a zone-refined copper surface indicate an initial degradation of about 30% for the surface containing 50-μm particles and little effect for the surface containing 500-μm particles. All surfaces conditioned to about the same voltage. Breakdown to all samples containing particles was clearly associated with metal-insulator boundaries.