Bremsstrahlung Emission in Strongly Coupled Plasmas

The bremsstrahlung process is an important mechanism for radiation transport in astrophysical, fusion, and industrial plasmas. Furthermore, plasmas created in these systems can often be in an intermediate coupling regime, where the average kinetic energy of particles is on the order of the potential energy at the average interparticle spacing. In this work we extend the classical theory of bremsstrahlung emission to strongly coupled plasmas. For emission greater than the plasma frequency, we find that the radiation spectrum can be described using binary collisions occurring through the potential of mean force. For emission lower than the plasma frequency, we show that the classical spectrum can be described using a force autocorrelation formalism that captures the effect of multiple collisions in sequence. This low-frequency limit gives a radiation spectrum that is dependent on the interspecies collision frequency calculated using a generalized Coulomb logarithm. In order to benchmark our theories, we consider a two-component plasma with repulsively interacting species and calculate the emission spectrum from classical molecular dynamics (MD) simulations for coupling strengths between 0.01-100. The theoretical predictions agree well with the MD simulations. We also compare the results to common classical approaches used for weakly coupled plasmas.