Bremsstrahlung Emission in Strongly Coupled Plasmas

Bremsstrahlung is an important mechanism for radiation transport in astrophysical, fusion, and industrial plasmas. These plasmas are often 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. This work presents mean force emission theory, which extends the classical theory of bremsstrahlung emission to strongly coupling. The theory utilizes a classical framework where only electron-ion interactions contribute to the emission spectrum. For emission much greater than the plasma frequency, the radiation spectrum can be described by solving for the electron trajectory during a binary collision where the electron-ion interactions occur through the potential of mean force. For emission near and lower than the plasma frequency, the spectrum can be described using autocorrelation functions that capture the effect of multiple collisions. First, we benchmark the theory using classical molecular dynamics (MD) simulations of a repulsively interacting two-component plasma. Next, we extend the theory to attractively interacting systems by using a pseudopotential to model the electron-ion interaction. At high frequencies, the pseudopotential leads to a decay of the spectrum in a qualitatively similar way as the repulsive case. The pseudopotential also allows for classically bound states to form in the MD simulations, leading to a peak in the emission spectrum that is absent in the repulsive case.