Improving the dicenter model for hot dense plasmas: molecular stark effect

International audienceIn previous work of the dicenter model, used to take into account the ionic correlation effects in hot dense plasmas, only considered a single perturbing ion (i.e., the nearest neighbor ion) thus limiting its range of applicability. The improvement proposed in the present work includes the effect of all perturbing ions through a quasistatic external microfield acting on a ``quasi-molecule''. This enlarges the domain of validity of the dicenter model. For low densities this new alternative model gives line widths in agreement with standard ``monocenter'' profiles without artificially reducing the electron screening inside the dicenter emitting cell. This reduced screening, which had been employed to treat the repulsive interactions between the quasi-molecule and the other perturbing ions, is removed in the present work. (C) 2001 Elsevier Science Ltd. All rights reserved

Advanced simulations of spectroscopic signatures of charge exchange in laser-produced plasmas

We present an advanced theory of charge-exchange-caused dips (also called X-dips) in spectral lines from laser-produced plasmas. We compare predictions of this advanced theory with our previously published experimental results where, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two X-dips in the $L_{\gamma}$ line of Al XIII perturbed by fully stripped carbon. We show that our advanced theory is in excellent agreement with our experimental results. From the practical point of view, our results open up a way to experimentally produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the results are important because 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 quasimolecular phenomenon that could be observed at relatively “low” densities of laser-produced plasmas

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

International audienceThe 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. (C) 2001 Elsevier Science Ltd. All rights reserved

Modeling the radiative properties of dense plasmas

International audienceA model aimed at describing the electronic structure of hot dense plasmas is presented. This model is first used to study the effect of the nearest neighbor interaction on the photoabsorption K-edge position in a dense fluorine plasma. Changes to the ionization potential lowering from the well-known ion sphere model [H. Nguyen er al., Phys, Rev, A 33, 1279 (1986)] are obtained by the present approach for plasma density above solid. We believe that this effect could be of importance in the calculation of the opacity of dense materials. The present model also provides an alternative to the treatment of line broadening in very dense plasmas where the average interionic spacing can be of the order of the spatial extent of the excited-state orbitals. To illustrate this point, we present F Lyman-beta line shapes for various density conditions

Aspects of plasma spectroscopy: Recent advances

Meeting on Radiative Properties of Hot Dense Matter III, LAWRENCE LIVERMORE NATL LAB, LIVERMORE, CALIFORNIA, 1996International audienceTwo important recent developments in Stark broadening are presented in this work: The first describes the Frequency Separation Technique (FST), which is motivated by the standard electron-ion separation and has important applications in that, coupled to any of a variety of methods capable of treating the intermediate ion-dynamical regime: (but not capable of treating ion impact), presents a unified and practical solution to the ion-dynamical problem. That is, this technique allows the relaxation of the quasistatic approximation. The second describes recent improvements that allow the accurate calculation of electron impact widths. (C) 1997 Published by Elsevier Science Ltd. All rights reserved

Two-centre bound states in hot dense plasmas

24th European Conference on Laser Interaction with Matter (ECLIM 96), MADRID, SPAIN, JUN 03-07, 1996International audienceA model for describing the transient molecular behavior in hot dense plasmas is presented and applied to the case of a transient F8+/F9+ molecular ion embedded in a dense (N-e approximate to 10(23) cm(-3)) fluorine plasma. Electron screening effects on molecular energy levels and on dipolar matrix elements are investigated for specific plasma conditions. The accuracy of the calculations is tested comparing values of the polarization shift of the FLy beta line as calculated from the present model to the ones determined in the framework of the Ion Sphere Model (ISM)

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

International audienceThis 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. (C) 2000 Published by Elsevier Science Ltd. All rights reserved