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Hugoniot, Reverberating Wave, and Mechanical Reshock
Measurements of Liquid Deuterium to 400 GPa Using Plate Impact Techniques
Marcus D. Knudson, Sandia National Laboratories
The high-pressure response of cryogenic liquid deuterium (LD2)
has been studied to pressures of ~400 GPa and densities of ~1.5 g/cm3.
Using intense magnetic pressure produced by the Sandia Z accelerator,
macroscopic aluminum or titanium flyer plates, several mm in lateral
dimensions and a few hundred microns in thickness, have been launched
to velocities in excess of 22 km/s, resulting in constant pressure drive
times of approximately 30 ns in plate impact, shock wave experiments.
This flyer plate technique was used to perform shock wave experiments
on LD2 to examine its high-pressure equation of
state (EOS). Using an impedance matching method, Hugoniot measurements
of LD2 were obtained in the pressure range of ~22–100
GPa. Results of these experiments indicate a peak compression ratio
of approximately 4.3 on the Hugoniot. In contrast, previously reported
Hugoniot measurements inferred from laser-driven experiments indicate
a peak compression ratio of approximately 5.5–6 in this same pressure
range. The stiff Hugoniot response observed in the impedance matching
experiments was confirmed in simultaneous, independent measurements
of the relative transit times of shock waves reverberating within the
sample cell, between the front aluminum drive plate and the rear sapphire
window. The relative timing was found to be sensitive to the density
compression along the principal Hugoniot. In fact, this reverberating
wave technique has proven to be more sensitive than the conventional
method of inferring density from the shock and mass velocity, at least
in this pressure regime. Finally, mechanical reshock measurements of
LD2 using sapphire, aluminum, and a-quartz anvils
were made. These results also indicate a stiff response, in agreement
with the Hugoniot and reverberating wave measurements. Using simple,
model-independent arguments based on wave propagation, the principal
Hugoniot, reverberating wave, and sapphire anvil reshock measurements
are shown to be internally self-consistent, making a strong case for
a Hugoniot response with a maximum compression ratio of ~4.3 to ~4.5.
The trends observed in the present data are in very good agreement with
several ab-initio models and a recent chemical picture model
for LD2, but in disagreement with previously reported
laser results. Due to this disagreement, significant emphasis is placed
on the discussion of uncertainties, and the potential systematic errors
associated with each mechanical measurement.
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