High voltage DC breakdown initiation of cleaned vs. non-cleaned 304 LMC and 304 L stainless steel electrodes

The effect of surface contamination, material grade and surface finish on high voltage DC breakdown has been investigated. A simplified parallel plane gap test geometry has been used to model the electron gun structure in the VA-889F klystron. This klystron has exhibited arcing between the stainless steel focus electrode and copper anode during in-process high-pot testing to 50 kV DC. The anode of the test geometry consisted of a 1.5" diameter OFHC copper plate machined to a 63 surface finish (R/sub a/ = 1.6 /spl mu/m) The cathode consisted of various test coupons of 0.25" in diameter with a 0.05" radius applied to the edge to minimize field enhancement.