INVESTIGATION OF THE MECHANISMS ASSOCIATED WITH GAS BREAKDOWN UNDER INTENSE OPTICAL ILLUMINATION

Studies were made of the breakdown threshold of mixtures of the inert gases to determine the effects of controlled impurity levels on the breakdown process. In these experiments it was found that at 50,000 mm Hg the breakdown threshold of a 1 per cent neon, 99 per cent argon gas mixture was lower than that for pure argon, even though at any given pressure the breakdown threshold of neon alone is greater than that for argon. Measurements of the pressure dependence of the breakdown threshold of the gas mixture show the importance of gas collisions in the development of breakdown at high pressures and suggest that radiation energy transport may be the diffusion-like loss reported earlier. To examine further the growth of the breakdown region, studies have been made of the expansion of the breakdown plasma using a high-speed image converter camera. These studies show an initial rapid growth of the luminosity region followed by a contraction and a slower reexpansion of the luminous plasma. Further studies of the expansion are being carried out to determine the role of radiation energy transport in the plasma growth. (Author) See also AD-619 825.