Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The state and the evolution of planetary cores, drown dwarfs and neutron star crusts is determined by microscopic properties, such as viscosity and thermal conductivity, of the dense and compressed matter of which such system are made of. Due to the inherent diffculties in modelling strongly coupled plasmas, where classical long-range Coulomb forces dominate interactions between ions while electrons are partially to fully degenerate, current predictions of transport coeffcients differ by many orders of magnitude. This not only affects our ability to understand the evolution of planets and evolved stars, but also impacts our ability to accurately predict the implosion material characteristics in inertial confinement fusion experiments. The response of the compressed matter to density perturbations gives rise to collective modes, either electrostatic or acoustic waves, that serve as an important tool to validate theoretical predictions. Until recently, only electron modes could be measured experimentally. With the recent advances in free electron laser technology, x-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter as well. Here, we present numerical predictions for these ion modes and demonstrate signifcant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. In particular, a strong diffusive mode around zero frequency arises which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.