In megabar shock waves, materials compress and undergo a phase transition to a dense charged-particle system that is dominated by strong correlations and quantum effects. This complex state, known as warm dense matter, exists in planetary interiors and many laboratory experiments (for example, during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions). Here, we apply record peak brightness X-rays at the Linac Coherent Light Source to resolve ionic interactions at atomic (ångström) scale lengths and to determine their physical properties. Our in situ measurements characterize the compressed lattice and resolve the transition to warm dense matter, demonstrating that short-range repulsion between ions must be accounted for to obtain accurate structure factor and equation of state data. In addition, the unique properties of the X-ray laser provide plasmon spectra that yield the temperature and density with unprecedented precision at micrometre-scale resolution in dynamic compression experiments. M aterials exposed to high pressures of 1 Mbar and above have recently been the subject of increased attention due to their importance for the physics of planetary formation 1-3 , for material science 4 and for inertial confinement fusion research 5 . The behaviour of shock-compressed aluminium is of particular interest because it has been proposed as a standard for shock-wave experiments 6 and is widely used for equation-of-state 7,8 and warm dense matter (WDM) 9,10 studies. At room temperature, aluminium has three delocalized electrons, so it provides a prototype for an ideal electron fluid. As temperatures and pressures increase, compressing and breaking ionic lattice bonds, strong ionic forces remain, resulting in significant deviations from a simple fluid.Simulations using density functional theory coupled to manyparticle molecular dynamics (DFT-MD) have evolved into an ab initio tool to explore this regime of high-pressure physics 11,12 . To date, these simulations have been used to predict physical properties derived from optical observations of particle and shock velocities. Studies of structural properties that are sensitive to many-particle electron-ion and ion-ion interaction physics 13 have been challenging 14 , although recent progress has been made using X-ray absorption spectroscopy 15,16 . Early experiments on fourth-generation light sources 17 have made use of X-ray diffraction and measured the structural evolution from elastic to plastic states 18 . However, pressures in the Mbar regime, as required for melting many solids, have only recently become available at the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS).Here we visualize, for the first time, the evolution of compressed matter across the melting line and the coexistence regime into a WDM state. The combination of high-power optical lasers and the X-ray beam at MEC provides high-resolution X-ray scattering at multi-Mbar pressures. Our data provide the io...

Indirect-drive hohlraum experiments at the National Ignition Facility have demonstrated symmetric capsule implosions at unprecedented laser drive energies of 0.7 MJ. 192 simultaneously fired laser beams heat ignition emulate hohlraums to radiation temperatures of 3.3 million Kelvin compressing 1.8-millimeter capsules by the soft x rays produced by the hohlraum. Self-generated plasma-optics gratings on either end of the hohlraum tune the laser power distribution in the hohlraum producing symmetric x-ray drive as inferred from the shape of the capsule self-emission. These experiments indicate conditions suitable for compressing deuterium-tritium filled capsules with the goal to achieve burning fusion plasmas and energy gain in the laboratory.With completion (1) and commissioning (2) of the National Ignition Facility (NIF) the quest for producing a burning fusion plasma has begun (3, 4). The goal of these experiments is to compress matter to densities and temperatures higher than the interior of the sun (5-7) which will initiate nuclear fusion and burn of hydrogen isotopes (8-10). This technique holds promise to demonstrate a highly efficient carbon-free process that will burn milligram quantities of nuclear fuel on each laser shot for producing energy gain in the laboratory.The NIF (11) consists of 192 laser beams that have been arranged into cones of beams to irradiate a target from the top and bottom hemispheres. This "indirect-drive" laser geometry has been chosen for the first experiments to heat the interior of centimeter-scale cylindrical gold hohlraums (8,(12)(13)(14)(15) through laser entrance holes (LEH) on the top and bottom end of the cylinder (Fig. 1). Hohlraums act as radiation enclosures that convert the optical laser light into soft x-rays that are characterized by the radiation temperature T RAD . Present ignition designs operate at temperatures of 270 to 305 eV or 3.1 to 3.5 million K. The radiation field compresses a spherical fusion capsule mounted in the center of the hohlraum by x-ray ablation of the outer shell. The ablation process compresses the cryogenically prepared solid deuterium-tritium fuel layer in a spherical rocket implosion. In the final stages, the fuel reaches densities 1000-times solid and the central hot spot temperatures will approach 100 million K to initiate the nuclear burn process.We have symmetrically imploded 1.8-mm diameter fusion capsules in cryogenically fielded centimeter-scale hohlraums at 20 K. These experiments show efficient hohlraum heating to radiation temperatures of 3.3 million K. In addition, the large scale-length plasmas encountered in these experiments have allowed us to use self-generated plasma optics gratings (16) to control the radiation symmetry (17) and to achieve symmetric fusion capsule implosions.Figure 2 A shows the laser power at the frequency-tripled wavelength of 351 nm versus time for two different pulse shapes. These 11-ns and 16-ns long pulses heat 8.4-mm long, 4.6-mm diameter hohlraums with 20% helium, 80% hydrogen (atomic) mixtures and ...

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.