Short-Time Radiative Processes in Exploding Metal Foil Plasmas

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Abstract
Spacially and temporally resolved spectra are described from explosions of Al foil strips in Ar at 100 and 700 Torr. Spectra were obtained photographically with a time resolution of 0.3 μs using a rotating mirror streaking camera. Measurements were made at 1, 2, 5, 10 and 15 mm above the foil surface with a spacial resolution of 0.1 mm. The early appearance of Ar ion lines for explosions in Ar at 100 Torr implies initial current conduction following foil vaporization via dielectric breakdown of the Ar. At 700 Torr, the complete absence of radiation from Ar ion lines suggests that gas-phase current conduction begins by dielectric breakdown of the metal vapor. The short duration of Ar ion radiation in any observation zone at 100 Torr coupled with the first appearance of radiation from metallic species during the period of decaying Ar intensity implies that the metal vapor is collisionally excited and ionized as it passes through the Ar current sheath. From the results of these studies, a dual-channel, photoelectric, gated integration procedure was used to obtain greater analysis line/background ratios. A two- to four-fold increase in line/background ratios is obtained when radiation from 15 mm above the foil is integrated during the interval from 25 to 125 μs after foil vaporization.