Shock Waves from Exploding Wires at Low Ambient Densities
Shock waves from exploding wires at subatmospheric density ρ 0 show considerable deviations from the ρ 0 − 1/4 dependence of shock radius expected on the basis of blast wave theory. The shock trajectory data are consistent with the assumption of time-dependent energy addition, and this fact suggests complexity in the mechanism of shock production. The recently discovered technique of streak interferometry has been applied to study 4-mil Cu wires exploded into argon at reduced pressures. Typical interferograms at 1/16 atm show an intensely luminous, peripheral arc formed in an annulus several millimeters from the wire. When filters are used to diminish the diffuse light from the glow, clear fringes can be reduced in the entire glowing region. Near the tip, measured fringe shifts are negative, indicating the presence of electrons. No shock wave is seen. During an interval of about 1 /µsec fringe shifts near the periphery of the expanding glow change to positive values, and a compressional shock wave can be seen to separate and propagate ahead. Estimates obtained from approximate interferogram reductions indicate electron densities as high as 1018cm−3 in the annular region of the arc. A sequence of interferograms at pressures of 1/16 to 1 atm is presented, and implications for the mechanism of shock production are discussed.
KeywordsShock Wave Shock Production Ambient Density Wire Material Fringe Shift
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