Breakdown of the vacuum gaps at the presence of tungsten dispenser cathodes

Summary form only given. Breakdown of the vacuum gaps in the presence of tungsten dispenser cathodes in the experimental diodes and triodes with external copper anodes was investigated. Investigations were carried out on the diodes with negative anode voltage up to 60 kV. Maximum breakdown field in the gap between the cathode and anode was determined by spasmodic increase of discharge number. Diodes were made with a smoothly changing distance between anode and cathode. On the results of the investigations with increasing length of the gap from 2 mm to 3.7 mm maximum breakdown field decreased from 1.9/spl times/10/sup 7/ V/m to 1.6/spl times/10/sup 7/ V/m. While increasing area of the electrodes by several times, maximum breakdown field did not decrease more than 5%. The surface of anode was investigated by means of the scanning electron microscope (SEM) and X-ray Microanalyzer (XMA). The SEM and XMA observations showed that anode surface was coated by separate fractions with dimensions of sides near 3 /spl mu/m and by compact cracked layer with the zones with dimensions near 6-12 /spl mu/m. The fractions and compact layers were on a base of barium. Triodes with tungsten dispenser cathodes were made with use of graphite grid in form of a disk with round holes and with the smoothly changing distance between the anode and grid. Investigations were carried out with positive anode voltage up to 40 kV and negative cut-off voltage on the grid. Maximum breakdown field in the anode-grid gap was determined by spasmodic increase of the discharge number.