27 марта наши гости из СЕА выступят на объединенном семинаре теор. отдела и нашей лаборатории

Post date: Mar 14, 2014 8:34:57 AM

Конференц-зал ул. Красноказарменная, 17-а.

11.00 – 11.30

Докладчик: Jean Clerouin

Название доклада: Self-organization in dense plasmas: the Gamma-plateau

When heated at constant volume (isochoric heating) a hot and dense plasma (10-5000 eV, 1-50 g/cm3) exhibits the same persistent microscopic structure (same static structure factor) over a wide range of temperatures [1]. In this steady-state regime, which depends on the chosen density and on the atomic number, the ionic thermal motion is essentially independent of the temperature and results in the subtle balance between ionization and temperature. This behavior, suggested by recent simulations, is confirmed by an analysis in the framework of the Thomas-Fermi scaling laws and was indirectly predicted years ago by I. P. Raizer and later by R. M. More. A simple analytical model is derived allowing for predicting the occurrence of this self-organized regime: the Γ-plateau [2]. This regime could be used to obtain well defined experimental conditions in electron heated isochoric experiments on buried layers.

[1] J. Clérouin, P. Arnault et al. Phys. Rev. E 87:061101, (2013).

[2] P. Arnault, J. Clerouin et al. Phys. Rev. E 88: 063106 (2013).

11.30 – 12.00

Докладчик: Pierre Noiret

Название доклада: SHOCK COMPRESSION OF DENSE PLASMA IN THE MNM TRANSITION SUPERCRITICAL DOMAIN

The Joint Institute for High Temperatures and the CEA-DAM are collaborating to prepare a hypervelocity launcher driven shock experiment on dense aluminum plasma. This experiment will be precursor to future laser driven shock experiments at higher pressure with the French “Laser Méga Joule” facility in Bordeaux [1]. This collaboration is focused on the investigation of the pressure metallization in dense plasma, in a range of temperature of 1 - 5 eV, of specific volume of 1 - 4 times larger than that of ambient solid, and of pressure of 10 – 40 GPa. The plasma target for the experiments will be produced using the pulse Joule heating technique developed at the JIHT [2,3]. This plasma target technique is being installed at the CEA-DAM in Arpajon. The hypervelocity launcher will be installed and operate by the CEA-DAM in its laboratories. In this presentation, we report on the progress of the CEA-DAM experimental contribution.

[1]. http://www-lmj.cea.fr/index.htm

[2]. V. N. Korobenko, A. D. Rakhel, A. I. Savvatimski , V.E. Fortov, Phys. Rev. B 71, 014208 (2005).

[3]. V. N. Korobenko and A. D. Rakhel, Phys. Rev. B 75, 064208 (2007).

12.15 – 12.45

Докладчик: Olivier Durand

Название доклада: Large scale molecular dynamics simulations of ejection at the free surface of shocked-loaded Cu and Sn metals under melt conditions

When a metal is shock-loaded, the reflection of the shock wave onto its free surface can lead to the ejection of a great amount of small (micron-scale) particles (ejecta). The development of hydrodynamic codes capable to predict the formation of these ejecta and in particular their size or mass distribution is a very complex task. Indeed, the mechanisms and physical properties involved in these extreme conditions are still far from being perfectly identified and modelled.

For a few years, we develop at CEA an original approach which consists in simulating ejection at atomistic scale by performing large scale molecular dynamics (MD) simulations (> 10⁸ atoms) on long time scales (typically 1 ns) [1-2]. Although such simulations are least 3 or 4 orders of magnitude smaller than usual scales of ejection, they bring a lot to the understanding and modeling of the phenomenon and they may provide a basis of comparison for further experimental and/or numerical studies in the macroscopic world. In particular, they show that the size distributions of the ejecta exhibit a generic behavior with the sum of two distinct terms (a power law dependence in the small size limit and an exponential dependence in the large size limit) that correspond to two distinct basic mechanisms of fragmentation. The power law strongly suggests the existence, whatever the scale at which the phenomenon is studied, of a 2D fractal fragmentation process within the framework of a percolation model, and the exponential dependence suggests the competition between internal and surface energies in the system.

[1] O. Durand and L. Soulard, J. Appl. Phys. 111, 044901 (2012)

[2] O. Durand and L. Soulard, J. Appl. Phys. 114, 194902 (2013)