Parallel TREE code for two-component ultracold plasma analysis

The TREE method has been widely used for long-range interaction {\it N}-body problems. We have developed a parallel TREE code for two-component classical plasmas with open boundary conditions and highly non-uniform charge distributions. The program efficiently handles millions of particles evolved over long relaxation times requiring millions of time steps. Appropriate domain decomposition and dynamic data management were employed, and large-scale parallel processing was achieved using an intermediate level of granularity of domain decomposition and ghost TREE communication. Even though the computational load is not fully distributed in fine grains, high parallel efficiency was achieved for ultracold plasma systems of charged particles. As an application, we performed simulations of an ultracold neutral plasma with a half million particles and a half million time steps. For the long temporal trajectories of relaxation between heavy ions and light electrons, large configurations of ultracold plasmas can now be investigated, which was not possible in past studies

Microfield distributions in strongly coupled two-component plasmas

The electric microfield distribution at charged particles is studied for two-component electron-ion plasmas using molecular dynamics simulation and theoretical models. The particles are treated within classical statistical mechanics using an electron-ion Coulomb potential regularized at distances less than the de Broglie length to take into account the quantum-diffraction effects. The potential-of-mean-force (PMF) approximation is deduced from a canonical ensemble formulation. The resulting probability density of the electric microfield satisfies exactly the second-moment sum rule without the use of adjustable parameters. The correlation functions between the charged radiator and the plasma ions and electrons are calculated using molecular dynamics simulations and the hypernetted-chain approximation for a two-component plasma. It is shown that the agreement between the theoretical models for the microfield distributions and the simulations is quite good in general.Comment: 18 figures. Submitted to Phys. Rev.

Molecular dynamics simulations of microfields in strongly correlated plasmas

We use molecular dynamics computer simulations to investigate the fluctuations of the electric microfield in a strongly coupled plasma. For a one-component plasma our results for the probability distribution bridge the gap between expressions obtained by cluster expansions valid for weakly coupled plasmas and those obtained in the simple harmonic oscillator model in the strong coupling regime. In a strongly coupled two-component plasma the dynamics does ceases to separate clearly into a fast electronic and a slow ionic component. Because of the formation of bound states the two-component autocorrelation functions for the electric field cannot be obtained by superposing the autocorrelation function of the electrons and ions. With increased coupling the conditional covariance of the microfield shows an increasing oscillatory behaviour as a function of time. This will influence the line shape of radiative transitions in the ions which is used as a tool for plasma diagnostics

Dense Plasma Dynamic Structure Factor Simulation Data vs. the Method of Moments

The dynamic structure factor of dense two-component plasmas is studied within the method of moments. A new model for the Nevanlinna parameter function is suggested. Our results on the dynamic structure factor satisfy the sum rules and other exact relations automatically, independently of the choice of a mathematically consistent model of the latter. A quantitative agreement is obtained with the molecular dynamics simulation data. Our approach permits to correct and complement the results of alternative approaches.The authors acknowledge the financial support of the Science Committee of the Ministry of Education and Sciences of the Republic of Kazakhstan (Grants numbers 3119/GF4, 3831/GF4), Yu.V. Arkhipov expresses gratitude for the financial support provided by the Ministry by a grant "The Best Professor" and I.M.T. is grateful to the KazNU for its hospitality. We are also grateful to G. Zwicknagel for providing numerical data published in [24].Arkhipov, YV.; Ashikbayeva, AB.; Askaruly, A.; Davletov, AE.; Syzganbaeva, S.; Voronkov, VV.; Tkachenko Gorski, IM. (2015). Dense Plasma Dynamic Structure Factor Simulation Data vs. the Method of Moments. Contributions to Plasma Physics. 55(5):381-389. https://doi.org/10.1002/ctpp.201400096S38138955