Phenomena occurring at Electrically Stressed Metallic Surfaces in Vacuum

CERTAIN hypotheses put forward to explain the mechanism of electrical breakdown of high vacuum, between metallic electrodes, rely on the removal from the electrode surfaces of aggregates of material 1,2 . Such aggregates have become known as ‘clumps’. By means of radioactive layers on the electrodes or spectroscopic analysis, material transfer during the pre-breakdown phase has been shown to occur 3–6 . Breakdown has been initiated by the introduction of particles of electrode material in the gap 7 . The occurrence of points and pits on the electrodes has been confirmed by examining the electrodes microscopically before and after voltage stressing, while actual growth and tearing off of small points several μ in length has been photographed during an increase in voltage 8,9 . The latter observations snowed that the points appeared to grow only on the anode, a fact supported by an observation that indicated the breakdown voltage was proportional to the tensile strength of the anode 10 .