Time filter

Source Type

Arpajon, France

Larroche O.,CEA DAM Ile-de-France
Physics of Plasmas | Year: 2012

Recently performed inertial confinement fusion implosion experiments involving D-3He gas-filled microballoons have shown discrepancies between expected and measured nuclear fusion yields as the relative abundances of D and 3He are varied. The latter have been tentatively attributed to a sedimentation, or stratification phenomenon occurring in the target core. This work investigates the possibility of ion species sedimentation in a detailed way through multi-species ion-kinetic Vlasov-Fokker-Planck simulations of the implosion process. A noticeable amount of sedimentation is found to build up during the main shock propagation to the target center, but then disappears as the implosion proceeds. As a result, only the yield of the first burst of neutrons, associated with shock convergence, is appreciably modified, leaving the main neutron production phase during fuel compression and stagnation unaffected. The sedimentation of fuel ion species found, thus, cannot explain the experimental discrepancies. © 2012 American Institute of Physics.

An analytic model is presented that predicts viscosity and diffusion of plasma for pure elements and multicomponent mixtures, from the high-temperature low-density weakly coupled regime to the low-temperature high-density strongly coupled regime. It relies on a pseudo-ion in jellium modeling that incorporates the effect of electron screening on the ion-ion interaction in the pseudo-ionization. Mixtures are treated using approximate kinetic expressions and mixing laws applied to the excess viscosity and self-diffusion of pure elements. Comparisons are made with classical and quantum molecular dynamics results to assess its accuracy. The mean deviations are in the range 20-40% with almost no predictions further than a factor of 2 over many decades of variation. Applications of this model in the inertial confinement fusion context could help in predicting the appearance and the growth of hydrodynamic instabilities. © 2013 Elsevier B.V.

Pellegrini Y.-P.,CEA DAM Ile-de-France
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

A theoretical framework is proposed to derive a dynamic equation motion for rectilinear dislocations within isotropic continuum elastodynamics. The theory relies on a recent dynamic extension of the Peierls-Nabarro equation, so as to account for core-width generalized stacking-fault energy effects. The degrees of freedom of the solution of the latter equation are reduced by means of the collective-variable method, well known in soliton theory, which we reformulate in a way suitable to the problem at hand. Through these means, two coupled governing equations for the dislocation position and core width are obtained, which are combined into one single complex-valued equation of motion, of compact form. The latter equation embodies the history dependence of dislocation inertia. It is employed to investigate the motion of an edge dislocation under uniform time-dependent loading, with focus on the subsonic/transonic transition. Except in the steady-state supersonic range of velocities - which the equation does not address - our results are in good agreement with atomistic simulations on tungsten. In particular, we provide an explanation for the transition, showing that it is governed by a loading-dependent dynamic critical stress. The transition has the character of a delayed bifurcation. Moreover, various quantitative predictions are made, that could be tested in atomistic simulations. Overall, this work demonstrates the crucial role played by core-width variations in dynamic dislocation motion. © 2014 American Physical Society.

Gaudefroy L.,CEA DAM Ile-de-France
Physical Review C - Nuclear Physics | Year: 2010

A systematic study of the low-lying structure of N=27, 28, and 29 isotones is performed within the shell model framework using the SDPF-U interaction. For each isotonic chain, correlation energy is found to increase while moving away from the stability line. Spherical shapes as well as small values of correlation energy are associated with the isotopes of 20Ca and 19K discussed in this study. Neutron intruder states appear at low excitation energy in the 18Ar and 17Cl studied isotopes. Coexistence between spherical and prolate deformed states is a systematic feature in 16S isotopes. Below Z=16 most of the studied nuclei are characterized by intruder ground states. The major role played by protons in determining the structure of N 28 nuclei is shown. © 2010 The American Physical Society.

An implementation of full self-consistency over the electronic density in the DFT+DMFT framework on the basis of a plane waveprojector augmented wave (PAW) DFT code is presented. It allows for an accurate calculation of the total energy in DFT+DMFT within a plane wave approach. In contrast to frameworks based on the maximally localized Wannier function, the method is easily applied to f electron systems, such as cerium, cerium oxide (Ce 2O 3) and plutonium oxide (Pu 2O 3). In order to have a correct and physical calculation of the energy terms, we find that the calculation of the self-consistent density is mandatory. The formalism is general and does not depend on the method used to solve the impurity model. Calculations are carried out within the Hubbard I approximation, which is fast to solve, and gives a good description of strongly correlated insulators. We compare the DFT+DMFT and DFT+U solutions, and underline the qualitative differences of their converged densities. We emphasize that in contrast to DFT+U, DFT+DMFT does not break the spin and orbital symmetry. As a consequence, DFT+DMFT implies, on top of a better physical description of correlated metals and insulators, a reduced occurrence of unphysical metastable solutions in correlated insulators in comparison to DFT+U. © 2012 IOP Publishing Ltd.

Discover hidden collaborations