Breakdown processes in large-area cold-cathode vacuum triodes
Preionization of large-aperture high-pressure discharge-pumped gas lasers requires uniform 250 to 500 keV 10 to 100 mA cm/sup -2/ electron beams of typically 1 to 10 x 10/sup 3/ cm/sup 2/ in area. Impedance collapse due to cathode plasma expansion renders diode electron guns inefficient in this application. Introduction of a control grid limits gun current to low, controllable values until plasma closure of the cathode-grid gap occurs. However, field enhancement at the grid can cause cathode-grid or grid-anode arcs resulting in current runaway. An experimental study of impedance collapse was conducted by measuring element I-V characteristics in a 20 x 200 cm cold-cathode triode electron gun. Impedance collapse of closure of the cathode-grid gap and (2) grid-anode arcs. Plasma closure rate was -2 x 10/sup 6/ cm sec/sup -1/ independent of configuration or interelectrode potential. Arc thresholds were found to depend (after conditioning) exclusively on local electric field strength at the grid which is, in turn, a function of grid bias and, more importantly, grid geometry. Streamers and arcs were occassionally observed in the cathode-grid region, phenomenon deserving of further investigation.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 6823677
- Report Number(s):
- LA-UR-84-2037; CONF-840981-3; ON: DE84014026
- Resource Relation:
- Journal Volume: EI-20; Journal Issue: 4; Conference: 11. international symposium on discharges and electrical insulation in vacuum, Berlin, F.R. Germany, 24 Sep 1984; Other Information: Portions are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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