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Home > Research Topics > Atomic and Molecular Physics in Plasmas

Atomic physics in hot and dense plasmas

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AVERROES code development

The treatment of arbitrary complex ions involves a myriad of energy levels and rates, thus requiring a proper averaging. Within that framework, the development of the AVERROES NLTE superconfiguration code has been pursued. In particular, by allowing for a partial splitting of the superconfigurations into simple configurations, it is possible to find a good convergence for the , the populations as well as the radiation power losses. Independently of this global convergence, a refinement procedure allowing for a more precise convergence on the spectrum itself (in emission or absorption) has been implemented.
Also, strong density effects are now taken into account in the code by including a density of free electrons in the ion cell in which all the structural quantities (energy levels and wavefunctions) are calculated. This density of the free electrons is calculated within the Thomas-Fermi approximation.
In parallel with the development of AVERROES, specific studies on fast reduced NLTE atomic models involving effective temperatures have been pursued.

Line broadening calculations

Spectral line shapes in hot plasmas submitted to a strong oscillating electric field have been theoretically studied by applying the standard hypotheses of plasma line broadening together with a nonpertubative Floquet treatment of the external oscillating field. The formulation has been applied to the lines of nonhydrogenic emitters like He-like and Ne-like ions. It is found that the simultaneous action of a strong oscillating field and plasma particle fields can lead to dramatic changes in the spectral emission. In particular, a laser-induced broadening of x-ray spectral lines allows one to imagine possible laser-controlled broadband ultra-fast X-ray sources.

Quantum trajectory theory of primary laser-atom interaction

We have performed a thorough comparison of classical and quantum pictures of laser-atom interaction to implement the Bohmian formalism with the aim to merge the qualitative and quantitative qualities of respective classical and quantum treatments. Bohmian mechanics are based on an hydrodynamic formulation of the time-dependent Schrödinger equation (TDSE) where the electronic flow is described in terms of fluid particles whose temporal evolution yields the so-called quantum trajectories. These trajectories do not evolve independently as in a classical framework, but are entangled through the action of a quantum potential that depends on the whole electronic density. Up to now, applications concern a model one-dimensional H atom imbedded in a strong and short laser pulse, and related Above-Threshold Ionization (ATI) and High-Order Harmonic Generation (HOHG).