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

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

A new algorithm for the solution and analysis of the Collisional Radiative Model equations

International audienceA new general algorithm for the solution of the Collisional Radiative Model (CRM) for large atomic models is presented. It is based on the separation of total population, and reduced populations for the individual states of each charge state. The sum of the latter is unity. This leads to a double linearized coupled iterative system, including cycling on all charge states. This algorithm is robust. It gives insight into the quality of the atomic model by allowing the follow up of the charge states populations, the global rates and the average charge Z* as a function of the iteration index. We show results on Xe with 39,683 configuration states

Improvements to the RADIOM non-LTE model

International audienceIn 1993, we proposed the RADIOM model [M. Busquet, Phys. Fluids 85 (1993) 4191] where an ionization temperature T z is used to derive non-LTE properties from LTE data. T z is obtained from an "extended Saha equation" where unbalanced transitions, like radiative decay, give the non-LTE behavior. Since then, major improvements have been made. T z has been shown to be more than a heuristic value, but describes the actual distribution of excited and ionized states and can be understood as an "effective temperature". Therefore we complement the extended Saha equation by introducing explicitly the auto-ionization/dielectronic capture. Also we use the SCROLL model to benchmark the computed values of T z