A. Benuzzi-Mounaix

Proton radiography as an electromagnetic field and density perturbation diagnostic (invited)

Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with million electron volt protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter.

Progress in the study of Warm Dense Matter

In the last few years, high power lasers have demonstrated the possibility to explore a new state of matter, the so-called warm dense matter. Among the possible techniques utilized to generate this state, we present the dynamic compression technique using high power lasers. Applications to planetary cores material (iron) will be discussed. Finally new diagnostics such as proton and hard-x-ray radiography of a shock propagating in a solid target will be presented.

Inhibition of fast electron energy deposition due to preplasma filling of cone-attached targets

We present experimental and numerical results on the propagation and energy deposition of laser-generated fast electrons into conical targets. The first part reports on experimental measurements performed in various configurations in order to assess the predicted benefit of conical targets over standard planar ones. For the conditions investigated here, the fast electron-induced heating is found to be much weaker in cone-guided targets irradiated at a laser wavelength of 1.057μm, whereas frequency doubling of the laser pulse permits us to bridge the disparity between conical and planar targets. This result underscores the prejudicial role of the prepulse-generated plasma, whose confinement is enhanced in conical geometry. The second part is mostly devoted to the particle-in-cell modeling of the laser-cone interaction. In qualitative agreement with the experimental data, the calculations show that the presence of a large preplasma leads to a significant decrease in the fast electron density and energy flux...

Electronic conduction in shock-compressed water

The optical reflectance of a strong shock front in water increases continuously with pressure above 100 GPa and saturates at ∼45% reflectance above 250 GPa. This is the first evidence of electronic conduction in high pressure water. In addition, the water Hugoniot equation of state up to 790 GPa (7.9 Mbar) is determined from shock velocity measurements made by detecting the Doppler shift of reflected light. From a fit to the reflectance data we find that an electronic mobility gap ∼2.5 eV controls thermal activation of electronic carriers at pressures in the range of 100–150 GPa. This suggests that electronic conduction contributes significantly to the total conductivity along the Neptune isentrope above 150 GPa.

COUPLING STATIC AND DYNAMIC COMPRESSIONS: FIRST MEASUREMENTS IN DENSE HYDROGEN

We demonstrate here a laser-driven shock wave in a hydrogen sample, pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P–T phase diagram of fluid hydrogen to high density. In this first-of-its-kind experiment, two hydrogen Hugoniot curves have been partially followed starting from pre-compression at pressures of 0.7 GPa and 1.2 GPa. Optical reflectance probing at two wavelengths reveals the onset of the conducting fluid state. The boundary line to conducting fluid hydrogen is suggested.

Absolute equation of state measurements of iron using laser driven shocks

First absolute equation of state measurements obtained for iron with laser driven shock waves are presented. The shock velocity and the free surface velocity of compressed iron have been simultaneously measured by using a VISAR diagnostic, and step targets. The pressure range 1–8 Mbar has been investigated, which is directly relevant to planetary physics. The experiments have been performed at the Laboratoire pour l’Utilisation des Lasers Intenses of the Ecole Polytechnique.

A laser experiment for studying radiative shocks in astrophysics

In this article, we present a laboratory astrophysics experiment on radiative shocks and its interpretation using simple modelization.The experiment is performed with a 100-J laser ~pulse duration of about 0.5 ns! which irradiates a 1-mm 3 xenon gas-filled cell. Descriptions of both the experiment and the associated diagnostics are given. The apparition of a radiationprecursorintheunshockedmaterialisevidencedfrominterferometrydiagrams.Amodelincludingself-similar solutions and numerical ones is derived and fairly good agreements are obtained between the theoretical and the experimental results.

Temperature and melting of laser-shocked iron releasing into an LiF window

Absolute reflectivity and self-emission diagnostics are used to determine the gray-body equivalent temperature of laser-shocked iron partially releasing into a lithium fluoride window. Pressure and reflectivity are measured simultaneously by means of velocity interferometer system for any reflector interferometers. In the temperature-pressure plane, a temperature plateau in the release is observed which is attributed to iron’s melting line. Extrapolation of data leads to a melting temperature at Earth’s inner-outer core boundary of 7800±1200K, in good agreement with previous works based on dynamic compression. Shock temperatures were calculated and found to be in the liquid phase.

X-ray source studies for radiography of dense matter

Studies of short-pulse laser-generated hard x-ray (18–60 keV) sources, suitable for radiographs of large samples of dense matter, are presented. The spatial and dynamic resolutions for different target types and laser parameters have been investigated. A high quality radiograph with good spatial resolution in two dimensions was demonstrated by irradiating freestanding thin W wires. The influence of the geometry for the quality of the radiograph, which is crucial for the design of experiments probing laser-compressed matter, is reported.

High pressures generated by laser driven shocks: applications to planetary physics

High power lasers are a tool that can be used to determine important parameters in the context of Warm Dense Matter, i.e. at the convergence of low-temperature plasma physics and finite-temperature condensed matter physics. Recent results concerning planet inner core materials such as water and iron are presented. We determined the equation of state, temperature and index of refraction of water for pressures up to 7 Mbar. The release state of iron in a LiF window allowed us to investigate the melting temperature near the inner core boundary conditions. Finally, the first application of proton radiography to the study of shocked material is also discussed.