Classical Bremsstrahlung in Strongly Coupled Electron-Ion Plasmas

Bremsstrahlung emission and inverse bremsstrahlung absorption are radiative processes that are important for energy transport in astrophysical objects, laser-produced plasmas, and nuclear fusion experiments. Importantly, many of these systems include plasmas that are moderately or strongly coupled, where the potential energy in the system is on the order of or exceeds the kinetic energy. Recent work has developed mean force emission theory -which extends theory for classical bremsstrahlung emission to describe strongly coupled plasmas- and tested it against molecular dynamics (MD) simulations of both positron-ion and electron-ion plasmas [1]. First, this talk shows how the Gaunt factor, and thus the emission and absorption coefficients, can be calculated classically from MD simulations using a general Kubo equation. For electron-ion plasmas, the attractive interactions and close quantum mechanical effects are modeled through the improved Kelbg potential (IKP). Attractive interactions generally increase the Gaunt factor relative to repulsive interactions. Strong attractive interactions can also lead to classically orbiting electrons that produce peaks in an emission spectrum. The IKP has the effect of introducing a decay at a frequency associated with the thermal de Broglie wavelength and decreasing the low frequency emission. Then, it is shown that mean force emission theory can be derived from the more general Kubo equation and can be used to describe the MD results. Mean force emission theory uses the potential of mean force to model electron-ion interactions. Finally, comparisons between mean force emission theory and the MD simulations in both repulsively and attractively interacting systems show that strong coupling introduces a large peak in emission and absorption around the electron plasma frequency.