On the influence of opacity variation on spatial structure of radiative shocks

International audienceWe provide a theoretical analysis of Radiative Shocks, defined as supercritical shocks accompanied by an ionization wave in front of the density jump. In particular, we look at the influence of opacity variation with temperature and photon energy on spatial structure of radiative shocks, with a view to understanding a split precursor feature observed in recent experiments. We show that multigroup processing, a more refined angular description and improved low temperature opacities are needed to explore the radiative precursor structure, at least in some temperature regimes where rapid change of ionization can be found

Measure of precursor electron density profiles of laser launched radiative shocks

We have studied the dynamics of strong radiative shocks generated with the high-energy subnanosecond iodine laser at Prague Asterix Laser System facilityComment: with small correction in Fig.1

Miniature shock tube for laser driven shocks

International audienceWe describe in this paper the design of a miniature shock tube (smaller than 1 cm3) that can be placed in a vacuum vessel and allows transverse optical probing and longitudinal backside XUV emission spectroscopy. Typical application is the study of laser launched radiative shocks, in the framework of what is called "laboratory Astrophysics"

Effect of incoming radiation on the non-LTE spectrum of Xe at Te = 100 eV

The effect of a diluted Planckian radiation field on a Xe gas at the electron temperature of 100 eV is investigated within the framework of a Collisional Radiative Model, using the HULLAC code. The atomic model spans 19 charge states, includes 20 375 configurations and contains more than 2 10^6 levels. We have simulated detailed spectra comprising more than 10^9 transitions with the Mixed UTA model. The radiation temperature Tr is varied from 0 to 1.5 Te. The dilution factor, D, applied to decrease the radiation field, is varied independently from 0 to 3 at fixed Tr = Te. In both cases, the average charge state Z* increases from 15 to 27, but in different ways. It is shown that even a dilution D = 0.01 changes Z* by more than 1.5. Different combinations of Tr and D yielding exactly the same Z*, may give line ratios sufficiently different to be observed. This fact is explained by the interplay of the shape of the radiation field and the atomic structure

Improved analytic fits of collisional cross-sections

International audienceComputing collisional cross-sections sigma( ε), where ε is the energy of the incident electron, is costly. Furthermore, for collisional-radiative models the thermally averaged cross-sections Te integrated over the distribution function of all electron energies is needed, so that one generally fits the collision strength Omega( ε) for 5-20 energies εi before an analytical or numerical integration is performed. However, in multi-charged, multi-electron ions, it is usual to find poor fits, which can lead to negative rates, for about 20% of the excitation transitions when one employs the classical Goett et al. fit (GCS) Omega(u=ε/DeltaE)=A+Dln(u)+c/(C+u)+c/( even when using the Bethe limit, also called Born or Coulomb-Born limit, at high energy as a constraint. From examples, we shall derive the requirement for an adequate fit and propose a tractable and efficient algebra to replace the GCS formula

Simulations of Fe at 156 eV with configuration interaction and mixed UTA

International audienceSimulations of the transmission spectra measured by Bailey et al. (Phys. Rev. Lett. 99 (2007) 265002-265004), obtained with the newest version of the HULLAC, are presented. With this new version one can easily define which group of configurations will be computed to synthesize the spectrum. Moreover, one can now compute mixed UTA (MUTA). These modifications provide an extension of the older HULLAC codes. The aim of this work is to compare spectra with different ranges of configuration interactions and with different thresholds for treating separated lines in the MUTA model