High-voltage hold-off of large surface area metal electrodes with dielectric surface layers

Aluminum and stainless steel electrodes with dielectric surface layers have been tested for the avoidance of electron emission and plasma induced arcs that limit high voltage hold-off. The aluminum dielectric coating is a 50-/spl mu/m-thick hard-anodized surface layer. Tests of the layer were made with and without a chemical etch to improve bonding to the machined aluminum. The coating on stainless steel is a 1-/spl mu/m-thick chromium oxide surface layer formed during high humidity hydrogen firing. Tests were performed on 15 and 17-cm-diameter electrodes, with 1.8 to 6 mm gaps. Tests were made with a 150 to 500 kV, 160-ns-FWHM waveform, with 1-cos(/spl omega/)t) shape. The electrodes were cleaned with acetone and installed into the vacuum chamber in a filtered clean air environment with <100 particles/m/sup 3/. Tests were performed with < 3x10/sup -6/ Torr vacuum. Data were obtained for virgin surfaces and as a function of accumulated damage from breakdown arcs. The anodized coatings gave maximum high voltage hold-off of 1.4 MV/cm when new and showed little degradation with 150-/spl mu/m-diameter damage craters in the cathode. Craters larger than 1-mm-diameter sometimes caused a factor of two degradation in hold off. It was less necessary to electrically condition the anodized surfaces to get optimum results. Results from each of the dielectric surface coatings and uncoated machined surfaces will be discussed.