The electron–ion collision frequency in a strong laser field is calculated in the framework of the quantum Vlasov theory in first-order Born approximation. Using a Wigner representation of the density matrix, the collision frequency can be expressed in terms of the Lindhard dielectric function and a close correspondence between classical and quantum-mechanical approaches can be obtained. Asymptotic formulas for the high-frequency collision frequency in weak and strong electric fields are obtained and compared with complete numerical calculations. The basic strong-field behavior can be explained in terms of the cold plasma model.

We describe the dynamics of electrons during and after the collision at large impact parameters between a highly charged ion and a cluster of from a few ten up to several hundred alkali-metal atoms. The theoretical model gives the time evolution of the electronic one-body phase-space density as the solution of the selfconsistent Vlasov equation. It allows us to predict the ionization state and the excitation energy of the cluster after collision. We demonstrate that with sufficiently charged ions it is possible to ionize metal clusters close to their Rayleigh charge limit without significant heating, thus providing a unique method to investigate charge instabilities in clusters.

High-fidelity nuclear power plant core simulations require solving the Boltzmann transport equation. In discrete ordinates methods, the most computationally demanding operation of this equation is the sweep operation. Considering the evolution of computer architectures, we propose in this paper, as a first step toward heterogeneous distributed architectures, a hybrid parallel implementation of the sweep operation on top of the generic task-based runtime system: PARSEC. Such an implementation targets three nested levels of parallelism: message passing, multi-threading, and vectorization. A theoretical performance model was designed to validate the approach and help the tuning of the multiple parameters involved in such an approach. The proposed parallel implementation of the Sweep achieves a sustained performance of 6.1 Tflop/s, corresponding to 33.9% of the peak performance of the targeted supercomputer. This implementation compares favorably with state-ofart solvers such as PARTISN; and it can therefore serve as a building block for a massively parallel version of the neutron transport solver DOMINO developed at EDF.

No abstract