A. Poquerusse

Observation of ion-ion correlation effects on emissivity and opacity of hot ultra-dense low Z plasmas

The transmission function and the resulting emissivity and opacity of bound-bound transitions in hot ultra-dense, low Z (aluminum or fluorine) plasmas are investigated in this paper. It is shown that the treatment of both the area-normalized line profiles and the absorption oscillator strengths involved are crucial. Taking account, self-consistently, of all the interactions inside a radiating transient molecule, as proposed in the dicenter code IDEFIX, we computed the photo-excitation cross-sections, the emissivities, the opacities, and then compare the results with those from standard codes. We emphasize the strong dependence of the above quantities with the ionic correlations. A first experiment, devoted to measure opacities and emissivities of hot and ultra-dense aluminum plasmas, has been designed. The interpretation of the results shows the adaptability of the dicenter model for these extreme conditions

Spectral line shapes using the dicenter approach for dense, hot plasmas: hydrogen and helium-like lines

Abstract This paper reports on the spectral line shape of hydrogen and helium-like lines relevant to the quasi-static dicenter model. This treatment is justified for hot dense, moderate Z plasmas. The code IDEFIX developed for the quasi-static dicenter model involves a self-consistent description of the interactions and of the radiative properties. Strong dependence of the transition energies and of the dipole moments on the interionic separation are pointed out and novel density-dependent spectroscopic features such as asymmetries, satellite-like features, molecular transitions are exhibited. The theoretical spectra presented here are discussed in connection with experimental results where these exist.

Access to Spectrally Resolved Ultra‐Dense Hot Low Z Emissivities and Opacities

We present here experimental studies of broadened bound‐bound emissivities and opacities of low Z plasmas that are the best candidates for exhibiting ion and electron correlations. First we report on an emission experiment where a new target design is used to access the highest densities. Such targets irradiated by an intense long laser pulse generate plasmas well adapted to model and extract opacities. The measurements are compared to theoretical results obtained from simulations involving new atomic/molecular physics models that take into account detailed line profiles. We end up with the description of an absorption experiment in progress, this experiment using the same targets.

Low Z opacities at high densities

Abstract We present an experimental study devoted to measuring the opacity of bound–bound transitions in ultra-dense, hot, low Z plasmas, which are at the extreme limit for conditions of both emission spectroscopy and absorption spectroscopy. In this work, we develop an absorption spectroscopy experiment specially adapted to high-density diagnostics, using newly designed structured targets and an ultra-high resolution spectrograph. An aluminum plasma is chosen as the first candidate and the opacity of the He-like 1s 2 –1s2p (He β ) and 1s 2 –1s3p (He γ ) transitions are measured.

Alternative treatment of line broadening in dense and hot plasmas

A spectral line shape code using the “quasimolecular model” has been developed for dense and hot plasmas. First this alternative treatment is justified. Then the importance of using a two-center basis and the effects of the plasma screening are discriminated. Specific hydrogen-like and helium-like transitions are studied for the exhibition of dense plasma effects (PPS, asymmetries, satellite features) and for a comparison with experimental results. It is shown that satellites due to extrema are enhanced by the ion dynamics correction.

Generation of hot and dense plasmas in laser accelerated colliding foil systems

We create hot ( T e > 200 eV) and dense ( N e > 10 23 cm −3 ) plasmas in the colliding zone of two thin foils accelerated by two laser beams of the LULI facilities. Three spectroscopic diagnostics (two 1D space-resolved spectrographs and a 2D monochromatic imaging) are used to drive the efficiency of the compression. We show that 2D effects are important. Realistic simulations of these experiments must be done, taking into account the inhomogeneity of the laser intensity in the focal spot, the foil distorsion, the plasma lateral expansion, and the lateral thermal conduction. Two-dimensional LASNEX code results are in good agreement with our experimental results. The optimized compressed plasmas generated are favorable for the exhibition of dense plasma effects due to molecular formations, and they reproduce in laboratory some astrophysical situations.

Advanced Simulations for Signatures of Charge Exchange in Heterogeneous Plasma Emission

We present an advanced theory of x‐dips in spectral lines emitted from laser‐produced plasmas. We compare predictions of this theory with our previous experimental results where, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two dips in the Lyγ aluminum line perturbed by fully stripped carbon. Our theory gives a reasonable agreement with our experimental results. The results are of importance for the diagnostics of fundamental processes as it opens up a way to experimentally produce not‐yet‐available fundamental data on charge exchange between multi‐charged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the x‐dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasi‐molecular phenomenon that could be observed at relatively “low” densities of laser‐produced plasmas, all those aspects emphasize the interest for studying heterogeneous plasma emission.

Time resolved FLy β spectroscopic measurements in colliding foil experiments

The experimental results we present here concern the time evolution of the main plasma parameters in the region between two thin laser accelerated Teflon foils as deduced from fluorine H-like and recombination continuum emission, as well as the time evolution of Fluorine Lyβ line profile. Two X-ray streak cameras with a time resolution of 10 ps have then been used, recording the emission of a 25 μm sized plasma slice between the foils, to be compared to the initial distance (≈100 μm). To obtain a well resolved spectrum despite of the low streak camera photocathode spatial resolution, a high dispersive TlAP spectrometer has been used to record the Lyβ line profile. In this way we can associate any particular line profile we record to the plasma conditions producing it. In conclusion this experiment allows quantitative comparison with hydrodynamics code results, post-processed by atomic physics and spectra codes.

Recent advances in spectroscopy of strongly correlated plasmas

The Quasimolecular Model using a Two Centre basis to describe the electronic emitting structure gives an alternative treatment of line broadening in dense and hot plasmas. Two codes are developed: IDEFIX for the radiative properties, QMSPECTRA (postprocessed to the first one) for the spectral line shapes. The observability of dense plasma effects (PPS, asymmetries and satellite features) in spectroscopic measurements is analysed within the proposed model and taking care of the eventual integrations over density gradients.

Spectroscopic diagnostics of 2D effects in dense plasmas. Comparison with 2D simulations

A space resolved spectrography and monochromatic imaging have been used for the laser-produced hot dense plasma diagnostics. Results are compared with 2-D plasma simulations. (AIP)