Search

Collisional and transport parameters for Cu are computed using the average atom model. Transition metals such as copper are difficult to model within the framework of the average atom model due to the presence of a narrow band of 3d electrons that mix and hybridize with the broad 4s band of nearly-free electrons. With electron temperature increasing, the 3d electrons play a key role in the thermodynamics and transport properties of Cu (Lin et al 2008 Phys. Rev. B 77 075133), as well as the stability of the lattice (Loboda et al 2011 High Energy Density Phys. 7 361). In this work, the average atom model was used to track the average energy of the 3d band and its evolution with electron temperature. At room temperature, its center is at ∼6 electron volts (eV), a few electron-volts below the Fermi energy, and with electron temperature increasing it sinks relative to it. At electron temperature of about 8 eV the 3d electrons leave the conduction band and become bound. A long-standing problem related to the average ion charge observed by conduction band electrons is addressed and successfully resolved. A work-around has been found that predicts the correct average ion charge, Z ˉ , by formally introducing a third group of electrons: quasi-bound electrons. Benchmarking with published data is made that shows good agreement.

We present a practical analysis of the fermion sign problem in fermionic path integral Monte Carlo (PIMC) simulations in the grand-canonical ensemble (GCE). As a representative model system, we consider electrons in a 2D harmonic trap. We find that the sign problem in the GCE is even more severe than in the canonical ensemble at the same conditions, which, in general, makes the latter the preferred option. Despite these difficulties, we show that fermionic PIMC simulations in the GCE are still feasible in many cases, which potentially gives access to important quantities like the compressibility or the Matsubara Greens function. This has important implications for contemporary fields of research such as warm dense matter, ultracold atoms, and electrons in quantum dots.

Extreme ultraviolet radiation from a high harmonic source has been used to measure the free-free attenuation coefficient and real refractive index of warm dense aluminium, with sample conditions of near solid density and temperature of 0.9 ± 0.23 eV. These were compared to results from the literature, where the measured attenuation coefficients showed some consistency with the modelling and existing data from a previous experiment. The absolute values of the attenuation coefficient were found to reside between the different sets of models for the warm dense matter (WDM) attenuation coefficient, and were found to be more in line with modelling and measurements of the cold opacity from the literature. Novel measurements of the real refractive index of WDM were also achieved—while ambiguity makes these measurements consistent with all the models, they prove useful as a proof-of-concept for future WDM studies.

The experimental data from investigations of optical properties of a strongly correlated plasma is an important cornerstone to construct theoretical models for the description of warm dense matter. The analysis of the response of a dense plasma to electromagnetic waves of moderate intensity can be used as a tool to investigate the validity of the physical models describing the behavior of matter under extreme conditions, high temperatures and pressures. The plasma created has transitive surfaces with a density profile. The research of the transitive layer of a explosively driven dense plasma can be carried out using the technique of inclined probing by polarized electromagnetic waves. Angular dependence of Sand P-polarized reflectivities at several wavelengths can be used in the integration of Maxwell equations to construct the spatial profile of the density of charge carriers. In this paper, we report new results of Sand P-polarized reflectivity measurements of a non-ideal plasma at νlas = 2.83·10 s (λlas = 1064 nm), νlas = 4.33·10 s (λlas = 694 nm) and νlas = 5.66·10 s (λlas = 532 nm). To generate the non-ideal plasma, we used explosively driven shock waves which lead to compression and irreversible heating of xenon and to measure the dense xenon plasma polarized reflectivity index, a pulsed RUBY and YAG+KTP system with a four-channel pulse high-speed device for determination of the Stokes vector components was used [1]. The device allowes to measure the intensity of the reflected laser beam for four azimuthal angles and was equipped with filters for selection of probing frequency. In order to determine the thermodynamic parameters and composition of plasma suitable calculations have been carried out. Working with a grand canonical ensemble, virial corrections have been taken into account due to charge-charge interactions (Debye approximation). Shortrange repulsion of heavy particles was considered within the framework of a soft sphere model [2-3]. In Figure 1, the experimental data and results of solving of Maxwell equations using the generalized Drude formula and the dynamical collision frequency in Born approximation [4] are shown. Results of calculations with layer temperature profile and ea-collisions as factor are shown in Figure 1 too.

As electronic structure simulations continue to grow in size, the system-size scaling of computational costs increases in importance relative to cost prefactors. Presently, linear-scaling costs for three-dimensional systems are only attained by localized or randomized algorithms that have large cost prefactors in the difficult regime of low-temperature metals. Using large copper clusters in a minimal-basis semiempirical model as our reference system, we study the costs of these algorithms relative to a conventional cubic-scaling algorithm using matrix diagonalization and a recent quadratic-scaling algorithm using sparse matrix factorization and rational function approximation. The linear-scaling algorithms are competitive at the high temperatures relevant for warm dense matter, but their cost prefactors are prohibitive near ambient temperatures. To further reduce costs, we consider hybridized algorithms that combine localized and randomized algorithms. While simple hybridized algorithms do not improve performance, more sophisticated algorithms using recent concepts from structured linear algebra show promising initial performance results on a simple-cubic orthogonal tight-binding model., 19 pages, 7 figures

To accelerate intense, short pulsed heavy ion beams to the energies of interest for studies of high energy density physics and warm dense matter, the Pulse Line Ion Accelerator (PLIA), of which the axial acceleration gradient can achieve several MeV per meter with realistic helix parameters at very low cost, was developed in recent years. A simple prototype of PLIA for a proof-of-principle experiment called the Lanzhou Test PLIA was designed and constructed at the Institute of Modern Physics in Lanzhou, and the test result matches the calculated result well. The pattern of the axial electric field Ez and the velocity of the traveling wave were simulated by CST.

The study of laser compressed matter, both warm dense matter (WDM) and hot dense matter (HDM), is relevant to several research areas, including materials science, astrophysics, inertial confinement fusion. X-ray absorption radiography is a unique tool to diagnose compressed WDM and HDM. The application of radiography to shock-wave studies is presented and discussed. In addition to the standard Abel inversion to recover a density map from a transmission map, a procedure has been developed to generate synthetic radiographs using density maps produced by the hydrodynamics code DUED. This procedure takes into account both source-target geometry and source size (which plays a non negligible role in the interpretation of the data), and allows to reproduce transmission data with a good degree of accuracy.

In this paper I discuss the subject of warm dense matter (WDM), which, apart from being of academic interest and relevant to inertial fusion capsules, is a subject of importance to those who wish to understand the formation and structure of planetary interiors and other astrophysical bodies. I broadly outline some key properties of WDM and go on to discuss various methods of generating samples in the laboratory using large laser facilities and outline some common techniques of diagnosis. It is not intended as a comprehensive review but rather a brief outline for scientists new to the field and those with an interest but not working in the field directly.

Over the past two years noteworthy experimental and theoretical progress has been made towards the top-level scientific question for the US programme on heavy-ion-fusion-science and high energy density physics: ‘How can heavy-ion beams be compressed to the high intensity required to create high energy density matter and fusion conditions?’ New results in transverse and longitudinal beam compression, high-brightness transport and beam acceleration will be reported. Central to this campaign is final beam compression. With a neutralizing plasma, we demonstrated transverse beam compression by an areal factor of over 100 and longitudinal compression by a factor of >50. We also report on the first demonstration of simultaneous transverse and longitudinal beam compression in plasma. High beam brightness is key to high intensity on target, and detailed experimental and theoretical studies on the effect of secondary electrons on beam brightness degradation are reported. A new accelerator concept for nearterm low-cost target heating experiments was invented, and the predicted beam dynamics validated experimentally. We show how these scientific campaigns have created new opportunities for interesting target experiments in the warm dense matter regime. Finally, we summarize progress towards heavy-ion fusion, including the demonstration of a compact driver-size high-brightness ion injector. For all components of our high intensity campaign, the new results have been obtained via tightly coupled efforts in experiments, simulations and theory.

In order to describe dielectric properties in dense plasmas, a consistent calculation of the collision frequency is required. We present new calculations for an electron gas at parameters which are relevant for warm dense matter. In particular, we focus on the influence of the different approximations for the collision frequency in the Gould–DeWitt scheme. We use the dynamic collision frequency in the Born, Lenard–Balescu and ladder approximation. The inclusion of collisions in a consistent manner modifies, e.g., the dielectric function significantly in the warm dense matter regime.

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.

Profiles of the H-alpha line calculated using the full computer simulation method (FCSM) and the standard theory (ST) agree excellently with a measured profile (at an electron density of Ne = 9.0 × 1016 cm−3 and temperature T = 12 600 K) in an argon–hydrogen (minority) arc plasma. Calculated widths (FCSM) and shifts (ST) also agree well with experimental data from flash-tube plasmas and gas-linear pinch plasmas. Some discrepancies are probably caused by experimental flaws. Our analysis of the so-called generalized theory (GT) shows that this theory is burdened with un-physical approximations, and consequently so are all subsequent modifications based on GT. It is shown that the so-called acceleration of the electron by the ion field (AEIF) effect is no new effect, but only a drastically simplified alternative model involving physical and algebraic errors, compared with traditional theory (ST, FCSM, etc) of the ion–electron interactions. A corrected, but still somewhat faulty, AEIF model yields an up to 15% increase of the half width of the H-alpha line (about 10% being contributed by unavoidable approximations and 3–5% by the pure AEIF effect, and worsening the agreement with experimental data) in contrast to the originally reported 25% decrease of the half width. Finally, we find that for plasma parameters Γ≤ 0.25 there is neither theoretical nor experimental evidence for the existence of the new 'warm dense matter effects' claimed in Escarguel et al (2000 Phys. Rev. E 62 2667), Flih et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 283), Escarguel et al (2000 J. Quant. Spectrosc. Radiat. Transfer 64 353) and Flih and Vitel (2001 Proc. 15th Int. Conf. on Spectral Line Shapes).

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.

We present Stark widths and shifts of the Hα line measured in a flash tube plasma in the electron density range Ne = (1– 4) × 1018 cm−3 and the temperature range T = 1–2 eV. The plasma parameters were measured independently of the width and shift of the Hα line. We found that the Hα widths and shifts, measured at two different plasma sources, producing 'warm dense matter' of similar parameters—the underwater discharge and the flash tube—are consistent with each other. Our experimental results are in a good agreement with Oks' theory of Stark widths and shifts. As a conventional reference, we also compared our experimental results with Griem's theory of Stark widths and shifts. For Griem's shifts we found discrepancies of up to 76%. Griem's widths lie mostly within the experimental error bars; however, their rms deviation from the most probable experimental widths is up to 44% greater than for Oks' widths. Therefore our experiment provides further proof of some new warm-dense-matter effects incorporated in Oks' theory, the most important of which is the acceleration of the perturbing electrons by the ion field.

The screened interaction potential between two compound particles, compound particle and charged particle (ion or electron) in multipole approximation for simulation of nonequilibrium warm dense matter are discussed. The density and temperature range has been considered at which the formalism of compound particles can be used. It is proposed that the presented screened potential can be useful for the simulation of the heavy ions in the presence of streaming electrons. Discussions about the implication of a compound particle picture for consideration of the dynamics of the beam of the charged particles in plasmas are given. The proposed model of interaction between heavy ions consists of dipole terms and the short range repulsion due to the Pauli exclusion principle.

We present a theoretical approach to derive the dc conductivity of warm dense matter (WDM) from x-ray Thomson scattering data. Predictions for the conductivity of aluminum at condensed matter densities are given within a wide temperature range ( eV). Strong correlation effects are taken into account by ionic structure factors. Screening and Pauli blocking are described via a pseudopotential. The results are compared with other theoretical models and simulations as well as with experimental measurements in the liquid metal regime and recent experiments in the WDM regime.

International audience; We present an overview of some recent theoretical and experimental results obtained on the properties of iron and silica at conditions encountered in planetary interiors. The first part is concerned with the development of x-ray absorption near edge spectroscopy in dynamical experiments using high-energy lasers as a tool to investigate phase transitions and structural changes at extreme pressure-temperature conditions for these two key constituents. The second part focuses on the development of a quasi-isentropic compression technique to achieve the pressure-temperature conditions anticipated in planetary interiors (3-10 Mbar, 5000-8000 K). The experiments were performed using the LULI, LLNL and LIL high-energy lasers' facilities. The experimental results are analyzed using first-principle simulations based on density functional theory.

A novel platform to measure the equation of state using a combination of diagnostics, where the spectrally resolved x-ray Thomson scattering (XRTS) is used to obtain accurate temperature measurements of warm dense matter (WDM) was developed for the OMEGA laser facility. OMEGA laser beams have been used to drive strong shocks in carbon targets creating WDM and generating the Ni He-alpha x-ray probe used for XRTS. Additional diagnostics including x-ray radiography, velocity interferometry and streaked optical pyrometry provided complementary measurements of density and pressure. The WDM regime of near solid density and moderate temperatures (1–100 eV) is a challenging yet important area of research in inertial confinement fusion and astrophysics. This platform has been used to study off-Hugoniot states of shock-released diamond and graphite at pressures between 1 and 10 Mbar and temperatures between 5 and 15 eV as well as first x-ray Thomson scattering data from shocked low density CH foams reaching five times compression and temperatures of 20–30 eV.

We provide theoretical analysis of the reflectance of shock compressed plasmas and warm dense matter for normal incidence of laser radiation as well as for the dependence of s- and p-polarized reflectivity on incidence angle. We use density functional theory approach for the calculation of the dielectric function and reflectivity. The Kohn-Sham set of equations with the projector augmented wave (PAW) potential is solved for valent electrons. Due to the nonlocality of the PAW potentials, the longitudinal expression for the imaginary dielectric function is used. The real part is obtained by the Kramers-Kronig transformation. Quantum molecular dynamics simulation and VASP is used. Comparison with the experimental data for shock compressed xenon is performed. Three wavelengths are considered.

Interaction of laser pulses with clusters creates non-equilibrium warm dense matter systems. In this work we deploy wave packets molecular dynamics to study initial stage of aluminum cluster relaxation after irradiation with 25-400 fs pulses.

In order to investigate properties of warm dense matter (WDM) in inertial confinement fusion (ICF), evaluation method for the WDM with isochoric heating on the implosion time-scale using an intense pulsed power generator ETIGO-II (~1 TW, ~50 ns) has been considered. In this study, the history of input energy into the sample is measured from the voltage and the current waveforms. To achieve isochoric heating, a foamed aluminum with pore sizes 600 μm and with 90% porosity was packed into a hollow glass capillary (o 5 mm × 10 mm). The temperature of the sample is calculated from the numerical calculation using the measured input power. According to the above measurements, the input energy into a sample and the achievable temperature are estimated to be 300 J and 6000 K. It indicates that the WDM state is generated using the proposed method with ICF implosion time-scale.

To understand its magnetohydrodynamic behaviors and the electrical properties, we proposed to evaluate both experimental observations and numerical simulations. Electrical conductivity for nickel in warm dense matter (WDM) state has been measured with an exploding wire in a quasi-isochoric vessel. The result shows that the electrical conductivity for nickel in WDM is relatively high from the comparison of the electrical conductivities for several materials in WDM state. However, the skin effect in the capacitor-coil target will be neglected from the estimation. A two-dimensional magnetohydrodynamic simulation for the capacitor-coil target has been demonstrated. The results shows that the distribution of B-field in the capacitor-coil target depends on the electrical conductivity model.

We have commenced experiments with intense short pulses of ion beams on the Neutralized Drift Compression Experiment (NDCX-II) at Lawrence Berkeley National Laboratory, with 1-mm beam spot size within 2.5 ns full-width at half maximum. The ion kinetic energy is 1.2 MeV. To enable the short pulse duration and mm-scale focal spot radius, the beam is neutralized in a 1.5-meter-long drift compression section following the last accelerator cell. A short-focal-length solenoid focuses the beam in the presence of the volumetric plasma that is near the target. In the accelerator, the line-charge density increases due to the velocity ramp imparted on the beam bunch. The scientific topics to be explored are warm dense matter, the dynamics of radiation damage in materials, and intense beam and beam-plasma physics including select topics of relevance to the development of heavy-ion drivers for inertial fusion energy. Below the transition to melting, the short beam pulses offer an opportunity to study the multi-scale dynamics of radiation-induced damage in materials with pump-probe experiments, and to stabilize novel metastable phases of materials when short-pulse heating is followed by rapid quenching. First experiments used a lithium ion source; a new plasma-based helium ion source shows much greater charge delivered to the target., Comment: 4 pages, 2 figures, 1 table. Submitted to the proceedings for the Ninth International Conference on Inertial Fusion Sciences and Applications, IFSA 2015

The matter in extreme conditions end station at the Linac Coherent Light Source (LCLS) is a new tool enabling accurate pump-probe measurements for studying the physical properties of matter in the high-energy density (HED) physics regime. This instrument combines the world's brightest x-ray source, the LCLS x-ray beam, with high-power lasers consisting of two nanosecond Nd:glass laser beams and one short-pulse Ti:sapphire laser. These lasers produce short-lived states of matter with high pressures, high temperatures or high densities with properties that are important for applications in nuclear fusion research, laboratory astrophysics and the development of intense radiation sources. In the first experiments, we have performed highly accurate x-ray diffraction and x-ray Thomson scattering measurements on shock-compressed matter resolving the transition from compressed solid matter to a co-existence regime and into the warm dense matter state. These complex charged-particle systems are dominated by strong correlations and quantum effects. They exist in planetary interiors and laboratory experiments, e.g., during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions. Applying record peak brightness x-rays resolves the ionic interactions at atomic (Angstrom) scale lengths and measure the static structure factor, which is a key quantity for determining equation of state data and important transport coefficients. Simultaneously, spectrally resolved measurements of plasmon features provide dynamic structure factor information that yield temperature and density with unprecedented precision at micron-scale resolution in dynamic compression experiments. These studies have demonstrated our ability to measure fundamental thermodynamic properties that determine the state of matter in the HED physics regime.

We have proposed a concept for generation method of warm dense matter (WDM) by using flyer impact accelerated by intense electron beams. To generate the warm dense matter by using flyer impact, the output current of electron beams generated by the intense pulsed-power generator as ETIGO-II is evaluated. The results denote that the beam current and the pulse duration are 11 kA and 50 ns, respectively. The achievable parameters of WDM by using flyer impact are estimated by the simplified model. It indicated that the sample temperature achieves the provided electron beams with lower conversion efficiency.

To improve a coupling efficiency for the fast ignition scheme of the inertial confinement fusion, fast electron behaviors as a function of an electrical conductivity are required. To evaluate the electrical conductivity for low-Z materials as a diamond-like-carbon (DLC), we have proposed a concept to investigate the properties of warm dense matter (WDM) by using pulsed-power discharges. The concept of the evaluation of DLC for WDM is a shock compression driven by an exploding wire discharge with confined by a rigid capillary. The qualitatively evaluation of the electrical conductivity for the WDM DLC requires a small electrical conductivity of the exploding wire. To analyze the electrical conductivity of exploding wire, we have demonstrated an exploding wire discharge in water for gold. The results indicated that the electrical conductivity of WDM gold for 5000 K of temperature has an insulator regime. It means that the shock compression driven by the exploding wire discharge with confined by the rigid capillary is applied for the evaluation of electrical conductivity for WDM DLC.

Property data in warm dense matter (WDM) are important to optimize implosion dynamics in a fuel pellet of inertial confinement fusion (ICF). A table-top pulsed power discharge device with isochoric heating using a sapphire hollow capillary was proposed, and was used to generate the extreme state of matter with a well-defined condition. We investigated numerically to generate the WDM by using the pulsed power discharge device. The numerical model was developed by time-dependent one-dimensional thermal diffusion with radiative transfer of multi-group approximation, and the numerical simulation was carried out according with the experimental condition. The achieved temperature of the numerical simulation result was confirmed by the previous experimental result. Also, the radiation energy density was shown at each group of the wavelength of emission.

To observe AC and DC electrical conductivity in warm dense matter (WDM), we have demonstrated to apply the spectroscopic ellipsometry for a pulsed-power discharge with isochoric vessel. At 10 μs from the beginning of discharge, the generated parameters by using pulsed-power discharge with isochoric vessel are 0.1 ρ s (ρ s: solid density) of density and 4000 K of temperature, respectively. The DC electrical conductivity for above parameters is estimated to be 104 S/m. In order to measure the AC electrical conductivity, we have developed a four-detector spectroscopic ellipsometer with a multichannel spectrometer. The multichannel spectrometer, in which consists of a 16-channel photodiode array, a two-stages voltage adder, and a flat diffraction grating, has 10 MHz of the frequency response with covered visible spectrum. For applying the four-detector spectroscopic ellipsometer, we observe the each observation signal evolves the polarized behavior compared to the ratio as I 1/I 2.

We have proposed a concept of experimentally estimating thermal conductivity in warm dense matter from the ruby fluorescence. To reduce the dimension of the system, a cylindrically arranged sample tamped by the ruby capillary has been considered. From the estimated ruby temperature, in which is simulated by the time-dependent thermal diffusion in equation, the ruby fluorescence can be obtained from 0.5 mm to 0.6 mm. The results indicated that the low density regime as ρ/ρs < 0.004 is possible to evaluate the ruby fluorescence.

An evaluation method for warm dense matter (WDM) with similar timescale in inertial confinement fusion (ICF) by isochoric heating using intense pulsed power generator ETIGO-II is considered for evaluating target behavior. The temperature increase of the sample is estimated from the numerical calculation using the measured current. As a result, in the case that the shape of sample is 2 mm x 10 mm and the density is 0.01 times solid density of copper, the temperature of sample increases up to 30000 K. It is expected that the WDM is generated using the proposed method with ICF implosion timescale.

The uniform electron gas (UEG) at finite temperature has recently attracted substantial interest due to the experimental progress in the field of warm dense matter. To explain the experimental data accurate theoretical models for high density plasmas are needed which crucially depend on treatment of quantum effects in electron-electron interaction as well as in the interaction of electrons with uniform positive background. To comply with these requirements we have developed the new quantum path integral model of the UEG and present the results of related direct path integral Monte-Carlo (DPIMC) simulations. Contrary to the known in literature approaches treating the electron-background interaction classically our simulations take into account the quantum effects in this interaction. We have observed very good agreement with known in literature results only up to moderate densities when the ratio of the average interparticle distance to the Bohr radius is of order four (rs ≥ 4) and observe deviations for higher densities. At very high electron density (rs ≈ 1) presented in literature approaches as well as our simulations are problematic due to the strong degeneracy of electrons and increasing fermion sign problem.

The permittivity of Lorentz plasmas and wide-range expression for effective frequency of collisions of electrons are considered in wide temperature range. The proposed expression fulfills all limiting cases (high- and low-frequency skin effect, degenerate and nondegenerate plasmas) and permits one to incorporate different physical phenomena in warm dense matter like contribution of electron-phonon collisions and umklamp process to permittivity. For the case of aluminum plasmas, the model takes into account both intraband and interband contributions to permittivity via semi-empirical Huttner model modified in such a way to ensure proper description of optical properties of aluminum at room temperatures.

An approach based on the chemical picture of plasma is proposed for the description of thermodynamics and the equation of the state of warm dense matter. Corresponding to this approach, the effects of Coulomb interaction, the short range repulsion of atoms and molecules, free electron degeneracy, and radiation pressure contributions are taken into account. A family of models based upon this approach is presented and discussed. The possibilities of these models for the description of strongly coupled plasma of hydrogen isotopes and noble gases under megabar and terapascal pressures under shock and isentropic compression are demonstrated. The asymptotic properties of the models at high temperatures are demonstrated, showing their application to the very accurate description of solar plasma.

We describe experiments designed to produce a bright M-L band x-ray source in the 3-3.5 keV region. Palladium targets irradiated with a 10(15) W cm(-2) laser pulse have previously been shown to convert up to similar to 2% of the laser energy into M-L band x-rays with similar pulse duration to that of the incident laser. This x-ray emission is further characterized here, including pulse duration and source size measurements, and a higher conversion efficiency than previously achieved is demonstrated (similar to 4%) using more energetic and longer duration laser pulses (200 ps). The emission near the aluminium K-edge (1.465-1.550 keV) is also reported for similar conditions, along with the successful suppression of such lower band x-rays using a CH coating on the rear side of the target. The possibility of using the source to radiatively heat a thin aluminium foil sample to uniform warm dense matter conditions is discussed.

International audience; Clusters excited by intense laser pulses are a unique source of warm dense matter, that has been the subject of intensive experimental studies. The majority of these investigations concern atomic clusters, whereas the evolution of molecular clusters excited by intense laser pulses is less explored. In this work we trace the dynamics of ${\rm C}{{{\rm O}}_{2}}$ clusters triggered by a few-cycle $1.45\;\mu {\rm m}$ driving pulse through the detection of XUV fluorescence induced by a delayed 800 nm ignition pulse. Striking differences among fluorescence dynamics from different ionic species are observed.

There is a range of thresholds in loading for the response of condensed phase matter, starting with inelastic deformation at the yield stress. Beyond this point compression continues until the material bond strength is overcome and becomes so-called warm dense matter. In this regime formulations of solid mechanics derived in the ambient state no longer apply. Between these two limits lies a boundary that differentiates weak- from strong-shock dynamic loading. This work examines these thresholds and shows a correlation between the theoretical strength of the material and this weak shock limit for a range of metals.

Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.

Experiments on the Z accelerator have demonstrated the ability to produce warm dense matter (WDM) states with unprecedented uniformity, duration, and size. Significant progress to combine x-ray Thomson scattering (XRTS), a powerful diagnostic for WDM, with the unique environments created at Z has been accomplished. The large current of Z is used to magnetically launch Al flyers to impact CH2 foam (0.12 g/cm3) samples. The uniformly-shocked CH2 foam volume is about 10 mm3 and the steady shock state lasts up to about 100 ns, which are approximately 1000 & 100 times larger, respectively, than typical laser shocked samples. The Z-Beamlet laser irradiates a 5 μm thick Mn foil near the load to generate 6.181 keV Mn-He-α x-rays that penetrate into the CH2 foam and scatter from it. A high sensitivity x-ray scattering spherical spectrometer with both high spatial and spectral resolution is fielded, which enables benchmark quality data by simultaneously measuring x-rays scattered from shocked and ambient regions of the CH2 foam, and the Mn x-ray source. Experimental efforts have achieved low x-ray background and mitigation of load debris, and measured high quality XRTS data of ambient CH2 foam have validated the technique.

Confined microexplosion produced by a tightly focused fs-laser pulse inside transparent material proved to be an efficient and inexpensive method for achieving high energy density up to several MJ per cm3 in the laboratory table-top experiments. First studies already confirmed the generation of TPa-range pressure, the formation of novel super-dense material phases and revealed an unexpected phenomenon of spatial separation of ions with different masses in hot non-equilibrium plasma of confined microexplosion. In this paper, we show that the intense focused pulse propagation accompanied by a gradual increase of ionization nonlinearity changes the profile and spectrum of the pulse. We demonstrate that the motion of the ionization front in the direction opposite to the pulse propagation reduces the absorbed energy density. The voids in our experiments with fused silica produced by the microexplosion-generated pressure above Young's modulus indicate, however, that laser fluence up to 50 times above the ionization threshold is effectively absorbed in the bulk of the material. The analysis shows that the ion separation is enhanced in the non-ideal plasma of microexplosion. These findings open new avenues for the studies of high-pressure material transformations and warm dense matter conditions by confined microexplosion produced by intense fs-laser.

We calculate the dynamic structure factor (DSF) in warm dense beryllium by means of ab initio molecular dynamics simulations. The dynamic conductivity is derived from the Kubo-Greenwood formula, and a Drude- like behaviour is observed. The corresponding dielectric function is used to determine the DSF. Since the ab initio approach is so far only applicable for wavenumbers k = 0, the k-dependence of the dielectric function is modelled via the Mermin ansatz. We present the results for the dielectric function and DSF of warm dense beryllium and compare these with perturbative treatments such as the Born-Mermin approximation. We found considerable differences between the results of these approaches; this underlines the need for a first-principles determination of the DSF of warm dense matter.

Using a linear mixture rule in which electron–electron, electron–atom and electron–ion interactions are considered, we calculate the electrical conductivity of iron and nickel plasmas from the expanded fluid domain to the warm dense matter regime. The plasma composition is obtained by the nonideal Saha equation. A nonmetal–metal transition predicted by the present model takes places in a moderate-density region and a relatively lower-temperature region. The effect of electron–atom electrical conductivity on the total electrical conductivity is evaluated and the average electron–atom momentum transport cross-section is calculated with density and temperature.

A study of isochoric heating of Al foil by laser-accelerated proton beam is presented. The proton source that induces the heating has been characterized in details. The heated sample conditions at different times during heating were inferred by coupling a time-and space- resolved interferometry diagnostic with a 1-dimensional hydrodynamic code (that includes proton stopping) that uses the previously characterized proton source as input. In this way, we have minimized the number of free parameters in the modeling of the heating. We have shown that heating was isochoric and almost uniform along the target thickness with a maximum temperature of ~ 18 eV. Finally, a X-ray Near Edge Absorption Spectroscopy (XANES) diagnostic has been used to study the structural modification of the warm dense aluminum sample. We have observed a progressive loss, within ~ 10 ps, of lattice ordering within solid density Al samples as the temperature rises from 300 K to > 104 K.

As a technique for heating matter to high energy density, intense beams of heavy ions are capable of delivering precise and uniform beam energy deposition to a relatively large sample. The US heavy ion fusion science program has developed techniques for heating and diagnosing warm dense matter (WDM) targets. We have developed a WDM target chamber and a suite of target diagnostics including a fast multi-channel optical pyrometer, optical streak camera, VISAR, and high-speed gated cameras. Initial WDM experiments heat targets by both the compressed and uncompressed parts of the NDCX-I beam, and explore measurement of temperature, droplet formation and other target parameters. Continued improvements in beam tuning, bunch compression, and other upgrades are expected to yield higher temperature and pressure in the WDM targets. Future experiments are planned in areas such as dense electronegative targets, porous target homogenization and two-phase equation of state.