Bulk viscosity of the rigid rotor one-component plasma

TL;DR

This study uses molecular dynamics simulations to explore the bulk viscosity of a model plasma with diatomic ions, revealing that rotational degrees of freedom can significantly influence bulk viscosity, especially in strongly coupled regimes.

Contribution

It introduces the rigid rotor one-component plasma as a new model to analyze the impact of molecular rotation on plasma bulk viscosity.

Findings

Bulk viscosity increases with Coulomb coupling strength.

Long-range Coulomb interactions lead to long rotational relaxation times.

Bulk-to-shear viscosity ratio varies with system parameters.

Abstract

Bulk viscosity of a plasma consisting of strongly coupled diatomic ions is computed using molecular dynamics simulations. The simulations are based on the rigid rotor one-component plasma, which is introduced as a model system that adds two degrees of molecular rotation to the traditional one-component plasma. It is characterized by two parameters: the Coulomb coupling parameter, $\Gamma$, and the bond length parameter, $\Omega$. Results show that the long-range nature of the Coulomb potential can lead to long rotational relaxation times, which in turn yield large values for bulk viscosity. The bulk-to-shear viscosity ratio is found to span from small to large values depending on the values of $\Gamma$ and $\Omega$. Although bulk viscosity is often neglected in plasma modeling, these results motivate that it can be large in molecular plasmas with rotational degrees of freedom.