Field shaping to improve vacuum diode voltage holdoff
A small vacuum diode which will reliably hold off a pulse voltage in excess of 150 kV is described. These diodes typically have an interelectrode spacing of 6 to 10 mm with a glass insulator length 3 to 4 times the interelectrode spacing. It was found that the overall holdoff voltage for a diode with a fixed insulator and interelectrode gap length was strongly affected by the position of the interelectrode gap. The highest voltage holdoff was obtained when the interelectrode space was at the negative end of the insulator. Experiments were made with two sizes of diodes, varying the location of the interelectrode space from the negative end to the positive end. The large diode high voltage holdoff ranged from 240 kV with the interelectrode space at the negative end to a minimum of 50 kV in the middle and returning to a 180 kV with the interelectrode space at the positive end. The smaller diode high voltage holdoff ranged from a high of 200 kV with the interelectrode space at the negative end to 130 kV with the interelectrode space at the positive end. The minimum at the middle was not as pronounced in this diode. Since most of the HV breakdowns were across the glass insulator, electron avalanching was suspected. Computer-generated field plots confirmed this possibility. With the interelectrode space at the negative end, the field lines direct any field emission electrons from the triple junction or the edge of the negative electrode away from the glass. All other configurations direct the electrons toward the glass. Shaping the field so that any field-emitted electrons are directed away from the insulator improves the HV holdoff by minimizing the probability of an avalanche type surface breakdown.
- Research Organization:
- General Electric Co., St. Petersburg, FL
- OSTI ID:
- 6221493
- Report Number(s):
- CONF-821024-
- Journal Information:
- IEEE Trans. Electr. Insul.; (United States), Vol. EI-18:3; Conference: 10. international symposium on discharges and electrical insulation in vacuum, Columbia, SC, USA, 25 Oct 1982
- Country of Publication:
- United States
- Language:
- English
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