Techniques for the Study of Breakdown between Large-Area Electrodes in Vacuum

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Abstract
From experiments dealing with electrical breakdown phenomena in vacuum, it is clear that at voltages below that level actually required to produce breakdown, there occurs a low-level electron emission from highly localized regions of the cathode surface. This paper illustrates a technique for measuring the dependence of current upon voltage from one such region, utilizing variations in brightness of a phosphor screen. The technique avoids the possible confusion of a total current measurement which can result from the presence of simultaneously emitting areas or which can result from emission from regions of the electrode structure whose contribution to total current is unsuspected. This paper further demonstrates a method for the detailed location of particular emitting areas on the electrode surface. The procedure involves as a first step, the determination of the approximate location of the emitting region of interest using a phosphor screen. Following this, the electrode under study is used as a cathode opposite a lead anode without breakdown. This serves to evaporate lead metal from the anode surface areas lying directly opposite the cathode emitters. It is believed that charged vapor from the anode moves toward the cathode under the influence of the applied field and is deposited in the immediate region of the emitter. Subsequently, this lead can be detected in the scanning electron microscope using solid-state x-ray analysis. This serves to identify the emission region.