The effects of electrode cleaning and conditioning on the performance of high-energy, pulsed-power devices

Abstract

-High-energy pulsed-power devices routinely access field strengths above those at which broad-area, cathode-initiated, high-voltage vacuum-breakdown occur (> le7 -3e7 V/m). Examples include magnetically-insulatedtransmission-lines and current convolutes, high-currentdensity electron and ion diodes, high-power microwave devices, and cavities and other structures for electrostatic and RF accelerators. Energy deposited in anode surfaces may exceed anode plasma thermal-desorption creation thresholds on the time-scale of the pulse. Stimulated desorption by electron or photon bombardment can also lead to plasma formation on electrode or insulator surfaces. Device performance is limited above these thrFsholds, particularly in pulselength and energy, by the formation and expansion d plasmas formed primarily fiom electrode contaminants. Insitu conditioning techniques to modify and eliminate the contaminants through multiple high-voltage pulses, low base pressures, RF discharge cleaning, heating, surface coatings, and ion-and electron-beam surface treatment allow access to new regimes of performance through control of plasma formation and modification of the plasma properties. Experimental and theoretical progress h m a variety of devices and small scale experiments with a variety of treatment methods will be reviewed and recommendations given for future work.

Stochastic Nature of Electrical Breakdown in Vacuum

“…Gas multiplicative mechanism cannot act either, because electron mean free path is much larger than the interelectrode gap. The increase of the avalanche mechanism contribution to breakdown initiation with the rise of pressure can be attributed to the fact that high pressure enlarges the adsorbed gas layer on the electrodes, which leads to a higher probability of avalanche charge exchange between the electrodes, and consequently of breakdown [12][13][14]. Figure 11 shows the dependence of vacuum diode breakdown voltage mean, maximum and minimum values on the inter-electrode gap width at p = 10 -4 Pa (10 -9 bar) (types 1, 2 and 3 vacuum diodes).…”