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International audience; We present an experiment performed in 2016 at the LULI2000 laser facility in which X-ray and XUV absorption structures of nickel hot plasmas were measured simultaneously. Such experiments may provide stringent tests of the accuracy of plasma atomic-physics codes used to the modeling of plasmas close to local thermodynamic equilibrium. The experimental setup relies on a symmetric heating of the sample foil by two gold hohlraums in order to reduce the spatial gradients. The plasma conditions are characterized by temperatures between 10 and 20 eV and densities of the order of 10$^{−3}$ g/cm $^3$-10$^{−2}$ g/cm$^3$. For the X-ray part, we investigate the 2p-3d and 2p-4d transitions, and for the XUV part, we recorded the $\Delta$n = 0 (n = 3) transitions, which present a high sensitivity to plasma temperature. These latter transitions are of particular interest because, in mid-Z plasmas, they dominate the Planck and Rosseland mean opacities. Measured spectra are compared to calculations performed using the hybrid opacity code SCO-RCG and the Flexible Atomic Code (FAC). The influence of a spectator electron on the calculated spectra is analyzed using the latter code.

Ultra-high-intensity lasers have opened up a new avenue for the creation and detailed spectral measurements of dense plasmas in extreme thermodynamic conditions. In this paper, we demonstrate the possibility of heating a dense plasma (ρ > 1 gcm−3) to a maximum temperature of 560 ± 40 eV using a few-Joule, relativistic-intensity laser pulse. Particle-in-cell, radiation-hydrodynamic and atomic physics simulation tools are used together for a full description of the plasma dynamics, from laser interaction to late-time expansion and x-ray emission, yielding overall good agreement with the spectral measurements. We discuss the sensitivity of our analysis to space-time gradients, non-equilibrium ionization processes and hot electron effects.

We analyzed the spectra of X-ray transmission through radiatively heated medium-Z plasma (Fe, Ni, Cu and Ge) measured at LULI2000 facility in the wavelength range of 2p–nd transitions. The analysis was performed using the statistical superconfiguration code SCO, two line-by-line opacity codes based on the HULLAC and FAC packages and a new hybrid statistical-detailed code SCORCG. The temperature and mass density of the samples were estimated from hydrodynamic simulations based on the cavity radiative temperature measurements. The theory–experiment agreement is relatively good in the wavelength range corresponding to the 2p–3d transitions except in the germanium case. In the wavelength range of the 2p–2d, n > 3 transitions a relatively good theory–experiment agreement was found in the copper case. As predicted by calculations the separation of the characteristic spin-orbit-split 2p–3d structures, absent in the iron measured spectrum, appears in the nickel spectrum and is visible in the copper and germanium spectra. Comparisons of the experimental transmission with calculations confirm the importance of the relativistic configuration interaction. The absorption strength of the measured germanium 2p–3d transition is much larger than that obtained from the codes. Spatial temperature and density gradients, relatively high in the germanium sample, may be at the origin of this discrepancy.

Opacities of four medium Z element plasmas (iron, nickel, copper and germanium) have been measured at the LULI-2000 facility in similar conditions: temperatures between 15 and 25 eV and densities between 2 and 10 mg/cm3, in a wavelength range (8–18 A) including the strong 2p–3d structures. Two laser beams from the LULI facility were used in the nanosecond-picosecond configuration. The NANO-2000 beam (at λ = 0.53 μm) heated a gold hohlraum with an energy between 30 and 150 J with a duration of 0.6 ns. Samples covering half a hohlraum hole were thus radiatively heated. The picosecond pulse PICO-2000 beam (at λ = 1.053 μm) has been used to produce a short (about 10 ps) X-ray backlighter in order to reduce time variations of temperatures and densities during the measurement. A crystal high-resolution spectrometer was used as the main diagnostic to record at the same time the non-absorbed and the absorbed backlighter spectra. Radiation temperatures were measured using a broadband spectrometer. 1D and 2D simulations have been performed in order to estimate hydrodynamic plasmas parameters. The measured spectra have been compared with theoretical ones obtained using either the superconfiguration code SCO or the detailed term accounting code HULLAC. These comparisons allow us to check the modeling of the statistical broadening and of the spin-orbit splitting of the 2p–3d transitions and related effects such as the interaction between relativistic subconfigurations belonging to the same non-relativistic configuration.

X-ray transmission spectra of copper, nickel and aluminum laser produced plasmas were measured at the LULI2000 laser facility with an improved target design of indirect heating. Measurements were performed in plasmas close to local thermodynamic equilibrium at temperatures around 25 eV and densities between 10−3 g/cm3 and 10−2 g/cm3. This improved design provides several advantages, which are discussed in this paper. The sample is a thin foil of mid-Z material inserted between two gold cavities heated by two 300J, 2ω, nanosecond laser beams. A third laser beam irradiates a gold foil to create a spectrally continuous X-ray source (backlight) used to probe the sample. We investigate 2p–3d absorption structures in Ni and Cu plasmas as well as 1s–2p transitions in an additional Al plasma layer to infer the in-situ plasma temperature. Geometric and hydrodynamic calculations indicate that the improved geometry reduces spatial gradients during the transmission measurements. Experimental absorption spectra are in good agreement with calculations from the hybrid atomic physics code SCO-RCG.

The international OPAC consortium consists of astrophysicists, plasma physicists and experimentalists who examine opacity calculations used in stellar physics that appear questionable and perform new calculations and laser experiments to understand the differences and improve the calculations. We report on iron and nickel opacities for envelopes of stars from 2 to 14 M ⊙ and deliver our first conclusions concerning the reliability of the used calculations by illustrating the importance of the configuration interaction and of the completeness of the calculations for temperatures around 15–27 eV.

This paper will present an experimental platform developed on LULI2000 to measure x-ray emission of non-LTE plasmas in well-defined hydrodynamic conditions thanks to implementation of a whole set of diagnostics, including time-resolved electronic and ionic Thomson scattering and self-optical pyrometry. K-, L- and M-shell spectra will be presented and the methodology, that has been developed to analyze them, discussed.

An x-ray grating spectrometer was built in order to measure opacities in the 50 eV to 250 eV spectral range with an average spectral resolution ⟨E/δE⟩ ∼ 50. It has been used at the LULI-2000 laser facility at Ecole Polytechnique (France) to measure the Δn = 0, n = 3 transitions of several elements with neighboring atomic number: Cr, Fe, Ni, and Cu in the same experimental conditions. Hence a spectrometer with a wide spectral range is required. This spectrometer features one line of sight looking through a heated sample at backlighter emission. It is outfitted with one toroidal condensing mirror and several flat mirrors cutting off higher energy photons. The spectral dispersion is obtained with a flatfield grating. Detection consists of a streak camera sensitive to soft x-ray radiation. Some experimental results showing the performance of this spectrometer are presented.

This paper deals with theoretical studies on the $2p\ensuremath{-}3d$ absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004--0.01 ${\mathrm{g}/\mathrm{cm}}^{3}$. The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of $2p\ensuremath{-}3d$ transitions has been studied with the help of the statistical superconfiguration opacity code sco and with the fine-structure atomic physics codes hullac and fac. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code rcg has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by sco. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the $2p\ensuremath{-}3d$ transitions have been investigated as a function of the atomic number $Z$. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code scric. The sensitivity of the $2p\ensuremath{-}3d$ structures with respect to temperature and density in medium-$Z$ plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the $\ensuremath{\Delta}n=0$ absorption in medium-$Z$ plasmas for astrophysical applications.

This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004-0.01 g/cm(3). The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code SCO and with the fine-structure atomic physics codes HULLAC and FAC. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code RCG has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by SCO. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code SCRIC. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the Δn=0 absorption in medium-Z plasmas for astrophysical applications.

The lifetime of solar-like stars, the envelope structure of more massive stars, and stellar acoustic frequencies largely depend on the radiative properties of the stellar plasma. Up to now, these complex quantities have been estimated only theoretically. The development of the powerful tools of helio- and astero- seismology has made it possible to gain insights on the interiors of stars. Consequently, increased emphasis is now placed on knowledge of the monochromatic opacity coefficients. Here we review how these radiative properties play a role, and where they are most important. We then concentrate specifically on the envelopes of $\beta$ Cephei variable stars. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally., Comment: 6 pages, 5 figures, in press (conference HEDLA 2010)

The 2p − nd absorption structures in medium Z elements present a valuable benchmark for atomic models since they exhibit a complex dependence on temperature and density. For these transitions lying in the X-ray range, one observes a competition between the spin-orbit splitting and the broadening associated to the excitation of complex structures. Detailed opacity codes based on the HULLAC or FAC suites agree with the statistical code SCO; but in iron computations predict higher peak absorption than measured. An addition procedure on opacities calculated with detailed codes is proposed and successfully tested.