Structural transitions in solids induced by intense femtosecond pulses from X-ray
free-electron laser are in the focus of this talk. Depending on the dose absorbed, the
irradiation can trigger an ultrafast electronic or structural transition in these materials. For very
high doses, transition from the solid to warm-dense-matter or to plasma state follows.
Dedicated theoretical modeling...
K-shell x-ray emission spectroscopy is a standard tool used to diagnose the plasma conditions created in high-energy-density physics experiments such as short-pulse heated buried microdot targets. In the simplest approach, the emissivity-weighted average temperature of the plasma can be extracted by fitting an emission spectrum to a single temperature condition. Recent work has shown that...
Laser-driven shock compression coupled to brilliant X-rays probes opens new research opportunities in the field of matter at extreme conditions allowing to answer questions relevant for planetary science. At beamline ID24 at ESRF (Grenoble, France) a High-Power laser was coupled to time-resolved X-ray Absorption Spectroscopy (XAS)[1]. The unique advantage represented by coupling XAS together...
Atomic structure profoundly impacts the material and radiative properties of dense plasmas. Accurate atomic models are critical to understanding the structure and evolution of stellar interiors, inertial fusion plasmas, and traditional and nuclear explosives. Even at a few times solid density, however, interactions between neighboring ions in a plasma may substantially modify the atomic...
This talk describes how the steady state atomic kinetics approximation can underestimate the electron temperature determined from K-shell lines in ps-time-scale transient plasmas. In particular we model the inferred temperature evolution of solid FeS targets used in opacity experiments at the Orion laser facility determined from the ratio of the sulfur He-alpha to Ly-alpha lines. Initially we...
When an ultra-intense (>10$^{18}$ W/cm$^2$) laser pulse interacts with a suitable target in the plasma state, relativistic electrons are accelerated. These electrons can emit high-energy photons (keV-MeV energy range) mainly through bremsstrahlung [1,2], mediated by the atoms and ions inside the target, and through synchrotron-like emission [3]. These emission processes can be exploited for...
The ultrafast absorption of laser energy in condensed matter results in strongly out-of-equilibrium material conditions, which evolve into warm dense matter (WDM). Understanding the fundamental processes of ultrafast energy relaxation and structural evolution in these extreme systems is crucial for a wide range of fields, from laser nano-surgery to laser-fusion research.
The generally...
Quantum degeneracy and thermal effects challenge atomic models of warm dense matter (WDM), a regime where partial ionization, interatomic bonding, and band structure can modify plasma response properties. We use real-time time-dependent density functional theory (TDDFT), a multi-center first-principles approach, to benchmark the predictions of an improved average-atom (AA) framework for WDM....
We propose a consistent approach to determine the screening potential in dense plasmas with inhomogenous free electron micro-space distribution. Based on a local density and temperature-dependent ion-sphere model, the Saha equation approach is extended to the regime of strongly coupled plasmas by taking the free-electron-ion interaction, free-free-electron-interaction, inhomogenous...
Matter under extreme high-energy-density (HED) conditions (e.g., at superhigh pressures from billions to trillions of atmospheres) are often encountered in stars and inertial confinement fusion targets. Such extreme HED matter can now be created on energetic laser/XFEL facilities and pulsed-power machines in laboratories. Accurate knowledge of extreme HED matter is essential to better...
We show data and first analysis of a recent (Feb 2022) experiment on the spectroscopic investigation of XFEL-heated Cu foil targets. Cu foils were irradiated by the tightly focused XFEL beam (~1μm focus, up till 300μJ in energy, European XFEL), which heats the target to approximately 100 eV during its duration (~25 fs). The XFEL photon energy was varied in the range 8.8-9.8 keV to scan...
The radiative properties of an atom or an ion surrounded by a plasma, are modified through various mechanisms. Depending on plasma conditions the electrons supposedly occupying the upper quantum levels of radiators no longer exist as they belong to the plasma free electron population. All the charges present in the radiator environment, electrons and ions, contribute to the lowering of the...
The collective behavior of a plasma is favored by the long range of electric and magnetic fields, and is well known to be able to excite waves with an oscillating electric field. For example, Langmuir waves are ubiquitous in many types of laboratory, fusion, and astrophysical plasmas. By using a classical equipartition theorem for a plasma in equilibrium, one can attribute half of the energy...
Standard atomic physics models in PIC simulation either neglect excited states, predict atomic state population in post processing only, or assume quasi-thermal plasma conditions.
This is no longer sufficient for high-intensity short-pulse laser generated plasmas, due to their non-equilibrium, transient and non-thermal plasma conditions, which are now becoming accessible in XFEL experiments...
The Linear Response Method (LRM) uses tabulated data obtained with a small number of radiation fields to replace inline steady-state non-local thermodynamic equilibrium (NLTE) collisional-radiative calculations for (nearly-) arbitrary radiation fields. The tabulated data includes first-order derivatives with respect to the frequency-dependent radiation, i.e. linear response coefficients. ...
The advent of x-ray free-electron lasers (XFELs) has enabled a range of new experimental investigations into the properties of matter driven to extreme conditions via intense x-ray-matter interactions. The femtosecond timescales of these interactions lead to the creation of transient high-energy-density plasmas, where both electrons and ions may be far from local thermodynamic equilibrium...
We propose a model of ion-electron plasma (or nucleus-electron plasma) that accounts for the electronic structure around nuclei (i.e. ion structure) as well as for ion-ion correlations. The model equations are obtained through the minimization of an approximate free-energy functional, and it is shown that the model fulfills the virial theorem. The main hypotheses of this model are 1) nuclei...
The spectrometer calibration station at LLNL is used to characterize and calibrate the many crystals used in the various geometries of the x-ray spectrometers regularly used at the National Ignition Facility (NIF). Such absolute calibration is essential for every experiment in order to extract meaningful results and properly diagnose the plasmas. We present the calibration of three NIF...
K-shell transitions of He-like species have been widely used to diagnose high-energy-density plasmas, including those in the inertial-confinement fusion experiments. Recently, Stark broadening of the krypton He-beta line was used for inferring the electron density in NIF compressed capsules [1,2] and suggested for diagnostics in Laser MegaJoule experiments [3]. Here, we report on the Stark...
The discrepancies between theoretically calculated and experimentally measured Iron opacities at the Sandia National Laboratory Z-pinch machine are hitherto still unexplained even after nearly a decade of effort. Theoretical opacities have neglected higher-order processes such as two-photon processes, i.e., two-photon ionization or Raleigh and Raman scattering and thus could be a potential...
X-ray free electron lasers (XFEL) provide some unique capabilities in high energy density physics due to their ability to create solid density plasmas on very short time scales. The plasmas produced from these systems are typically far from LTE due to the large radiation field and short time scales. In recent years, collisional-radiative (CR) atomic kinetics codes have been adapted to handle...
