The effect of electrode contamination, cleaning and conditioning on high-energy pulsed-power device performance

Abstract

High-energy pulsed-power devices routinely use field strengths above those at which broad-area, cathode-initiated, HV vacuum-breakdown occur (>10/sup 7/ to 3/spl times/10/sup 7/ V/m). Examples include magnetically-insulated transmission lines and current convolutes, high-current-density 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 also can lead to plasma formation on electrode or insulator surfaces. Device performance is limited above these thresholds, particularly in pulse length and energy, by the formation and expansion of neutral and plasma layers formed primarily from electrode contaminants. In-situ conditioning techniques to modify and eliminate the contaminants through multiple HV 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 from a variety of devices and small scale experiments with a variety of treatment methods are reviewed and recommendations given for future work.