Breakdown Characteristics of Oxygen-Free Copper Electrodes in Ultrahigh Vacuum

Abstract

Oxygen-free copper is widely used in such devices as particle acceleraters, satellites, surface analyzers etc. Under ultrahigh vacuum condition electrical breakdown will be influenced by electrode bulk conditions such as gas absorption, impurity contents etc. as well as the electrode surface conditions. Using an in situ electrode surface cleaning system, the vacuum breakdown strength of vacuum degassed oxygen free copper electrodes satisfying ASTM-F-68 specification of Class 1, Class 3 and Class 5 is measured. Breakdown experiments reveal that the conditioning effect of vacuum gap is most significant in Class 1 electrodes. Any Class 1 electrode processings, except for annealing, do not improve the breakdown field at the first voltage application after the processing. The electrode annealing processing in vacuum environment is effective in improving the breakdown field at the first voltage application. It is discussed that the annealing releases the mechanical stresses due to electrode surface shaping.