For development of high-voltage equipment such as vacuum circuit breakers, it is very important to improve their dielectric breakdown characteristics in a vacuum. It is thus necessary to clarify the breakdown mechanism in a vacuum. It is well-known that these characteristics are influenced by the electrode material and its surface condition and the breakdown voltage is increased by current conditioning and electron beam irradiation [1] [2] [3] . This paper presents breakdown characteristics and observations of a cross-section after electron beam treatment and current conditioning treatment. The results are compared with those for only electron beam treatment and only current conditioning treatment. It is shown that the breakdown voltage of a CuCr electrode both treatments is higher than that achieved by only one of them. Treatment combining electron beam and current conditioning forms a CuCr layer with small Cr grains. The breakdown voltage after both these treatments is increased by the formation of this layer.
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