EFFECT OF ALUMINA INCLUSIONS ON THE BREAKDOWN AND EMISSION PROPERTIES OF COPPER SURFACES IN VACUUM

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.