Measurements of a Low Impedance, Large Area 100 kV Diode
A 25 cm by 60 cm cathode is used to produce 100 to 200 nsec electron beams of up to 350 kA at voltages less than 150 kV. A 2 to 3 nH tube is driven by a very low inductance dc-charged capacitor circuit whose characteristics are 200 kV, 220 nF and 16 nH. Cold cathodes comprising arrays of metal wires or ribbons have been used. The impedance obeys Child’s Law for space charge limited planar flow at early times. If constant velocity plasma closure between the anode and cathode is assumed, the impedance remains consistent with Child’s Law for times up to 250 nsec and for impedances and voltages as low as 25 milliohms and 3 kV. On this model, the apparent plasma velocity is very constant for most of the pulse duration, extremely uniform and reproducible, and depends mainly on the cathode material. Despite the agreement of impedance with a plane parallel flow model, strong pinching is observed in the diode. A uniform line pinch is formed, 60 cm long by about 1 cm wide. Pinch current has been measured as a function of time. The average electron flow is at a very small angle to the tungsten anode. Tungsten is vaporized and melted on each pulse, but the quantity of material removed is much smaller than expected. It is possible that the pinched beam deposits its energy in a depth of the anode that is much smaller than the electron range.
KeywordsPlasma Spacing Sulfur Hexafluoride Cold Cathode Atmospheric Pressure Sulfur Electron Range
Unable to display preview. Download preview PDF.
- 1.P. Champney, “Some Recent Advances in Three Electrode, Field Enhanced Triggered Gas Switches,” presented at Conference on Energy Storage, Compression, and Switching, Torino, Italy, November 1974.Google Scholar
- 2.C. D. Child, Phys. Rev. 32, 492, (1911).Google Scholar
- 3.P. Spence, Physics International Company, San Leandro, California, private communication.Google Scholar