Experimental Study of Condensation in Expanding Metal Vapors and Implications for ICF Target Chambers

Condensation within rapidly expanding metal vapors has been experimentally investigated by exploding wires in a test chamber filled with helium or argon at various pressures (10 millitorr to 760 torr). Lead and silver wires were vaporized using a 5.0 kV, 15.4 - 500 µF capacitor discharge system. It was observed that the metal vapor prefers to condense as droplets with a resulting fog or aerosol cloud as opposed to surface condensation. The debris analysis showed that the resulting aerosol particles were spherical and the size ranged from 0.02 to 0.2 microns, suggesting the vapor condensed by homogeneous nucleation. The time-dependent conditions of the expanding vapor were simulated using a 1-D hydrodynamics code. The calculations indicate that the vapor quickly becomes super-saturated due to expansion cooling. The implications of our results for nucleate condensation in ICF target chambers are also discussed.