The generation of shock waves by laser plasmas in water
confinement regime consists in irradiating with a pulsed and
focused laser beam a metallic target covered with a few
millimeters depth water layer. Laser energy is absorbed by
the target and produces a high-pressure plasma. The shock
waves induced by these dense plasmas have been investigated
for the first, second and third harmonics of Nd:Glass laser
and 0.6, 3 and 25 ns pulse durations. Shock wave
characterization, in terms of peak pressure and pressure
duration, have been performed using a Velocimetry
Interferometer System for Any Reflector (VISAR),
electromagnetic and piezoelectric PVDF gauges. Experimental
results have been analyzed using 1D simulation code taking
into account water confined interaction and shock wave
behavior in target material. The comparison of different
diagnostics shows that the VISAR measurements give more
precise results and allow accurate shock wave calibrations
as a function of irradiation conditions. Above a laser
intensity threshold depending on laser parameters, the peak
pressure is saturated to 6 GPa and pulse duration is reduced
due to breakdown plasma occurring in the confining water.
However, the pressure levels induced by confined plasmas are
high enough for surface processing and the technique is well
suited for investigating material properties under very high
deformation rate.
[C2.02] Electrical Conductivity of Water at 70-220 GPa
R. Chau, A. C. Mitchell, W. J. Nellis, R. Minich (Lawrence Livermore National Laboratory)
Electrical conductivities of water were measured in the pressure range 70-220 GPa using a reverberating shock wave obtained by the impact of a planar projectile onto a sample held between two stiff anvils. The planar projectile was accerlerated to velocities up to 7 km/s using a two-stage light gas gun. The conductivity of water varies from 40 to 200 Ømega^-1 cm^-1 between 70 GPa and 220 GPa. Our results are consistent with a purely protonic conduction mechanism at these conditions and are in agreement with recent ab-initio molecular dynamics calculations(C. Cavazzoni, G. L. Chiarotti, S. Scandolo, E. Tosatti, M. Bernasconi, and M. Parrinello, Science (in press)). The data will be compared to recent results for fluid hydrogen which undergoes a transition from a semiconducting to metallic fluid in the same pressure range and CH_2 which is an insulator.
[C2.03] Water shock Hugoniot measurement up to less than 1 GPa
Kunihito Nagayama, Yasuhito Mori, Katsuya Shimada (Kyushu University), Motonao Nakahara (Fukuoka Institute of Technology)
A sensitive detection of water shock front was realized by
using the difference in the pressure dependence of
refractive index of water and glass prism. Due to the
drastic increase in the refractive index of water by shock
compression, it is possible to design the target assembly
with an optical prism at the bottom of which the illuminated
light is totally reflected. Shock impedance mismatch method
was used to measure the shock Hugoniot in pure water by a
high-pressure gas gun up to less than 1 GPa. It is confirmed
by the experiment that the above-mentioned mechanism of
shock detection works very well down to the shock pressure
of 0.2 GPa. By using this method, shock compression curve
was measured up to about 1 GPa. Results were discussed by
comparing them with the previous data, which are found to be
scattered around the obtained data. It should be stressed
that the slope of the shock velocity particle velocity
Hugoniot in this region is very large, and the exact value
of it is of essential importance in evaluating the shock
state of water. Shock Hugoniot loci on pressure temperature
plane were calculated by using the present data.
[C2.04] Electrical conductivity and electrochemical phenomena in water shocked to the 110 GPa pressure range
V.V. Yakushev, V.E. Fortov, N.A. Kovalchuk, V.I. Postnov, T.I. Yakusheva (Institute for Chemical Physics Research RAS, Chernogolovka, 142432 Russia)
Electrical conductivities of water were measured during multiple shock compression in the pressure range 13 - 110 GPa. In the experiments two identical 4-points manganin gauges were Polyethylene (PE) encapsulated and placed between stainless steel anvils. Water specimen was formed by a small cavity inside the PE. It has electrical contacts with two coppered outlets of one of the gauges. The bridge of this gauge played the role of the shunt resistor for the water specimen. As a rule in the experiments we could resolve 3-4 individual shock reflections and measure water resistivity in each of them. The value of water resistivity was changed from 0.6 ohm cm at 13 GPa to approximately 0.012 ohm cm at 100 GPa. Insulation properties of PE under the multiple shocks were checked in separated experiments. In electrochemical experiments galvanic cells with electrodes of different metals and water as electrolyte were subjected to multiple shock loading and their electrical responses were measured. The ionic nature of the water conductivity was confirmed by these experiments.
[C2.05] A Reinterpretation of Reflected Wave N_2 Data.
J.D. Johnson (LANL, Los Alamos NM 87545.)
In a single second-shock modeling for the reflected wave N_2 data,(W.J. Nellis et al.,J. Chem. Phys. 94, 2244(1991)) one must invoke a, thermodynamically allowed but strongly anomalous, negative Grüneisen parameter through the dissociation region with standard positive values to either side. This causes the reflected Hugoniot to steepen sharply, then soften quite enough at higher pressures that for the higher data points the assumption of a stable second shock is incorrect. This analysis is thus contradictory. We reanalyze N_2 allowing for a multishock/adiabatic compression reflected wave. We find that the data is fully consistent with such a picture, including a more standard small, but positive, Grüneisen parameter for dissociation. The reflected wave is more accurately described by an adiabat rather than a single shock Hugoniot, thus explaining the low temperatures seen behind the wave. Although the dissociation softening responsible for the composite reflected wave is smaller for H_2, it is quite likely that a similar description applies. This complex wave interpretation is a more natural and consistent picture than that offered by the single second shock/negative Grüneisen parameter. The experimental observation of composite waves is quite interesting.
[C2.06] Liquid nitrogen thermodynamic and conductivity properties under multiple shock compression.
Alexandr Filimonov, Sergei Kvitov, Dmitry Nikolaev (), Vladimir Ternovoi (Institute for Chemical Physics Research, Chernogolovka, 142432 Russia)
A serie of experiments was performed to investigate nitrogen thermodynamic and conductivity properties, in which nitrogen was shock compressed between steel driver and sapphire window. Manganin pressure gauge, fast optical pyrometry and electrical resistance measuring systems were used to registrate nitrogen thermodynamic properties and conductivity simultaneously. The states of nitrogen with pressure up to 160 GPa and density about 5g/cm^3 were achived. Experimental results were compared with 1D hydrocode simulation using semiempirical EOS and conductivity models.