Measurement of the adiabatic index in be compressed by counterpropagating shocks.
We report on the first direct measurement of the adiabatic index γ through x-ray Thomson scattering from shock-compressed beryllium. 9 keV x-ray photons probe the bulk properties of matter during the collision of two counterpropagating shocks. This novel experimental technique determines γ by using only the measured mass densities and vanishing particle velocity at the point of shock collision to close the Rankine-Hugoniot equations. We find γ>5/3 at 3× compression, clearly different from ideal gas behavior. At 6× compression, γ shows the convergence to the ideal gas limit, in agreement with linear scaling laws.
Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
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C
Fortmann
H J
HJ
Lee
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Döppner
R W
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Falcone
A L
AL
Kritcher
O L
OL
Landen
S H
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Glenzer