Molecular Dynamics Simulations of Ion-Electron Temperature Relaxation Rates for Strongly Magnetized Antimatter Plasmas*

Antimatter appears in minuscule quantities relative to matter in nature for reasons not yet fully understood. A better understanding of the fundamental physics governing antimatter is needed to aid in addressing this open question.  The ALPHA experiment at CERN is working to improve our understanding of antimatter by trapping antihydrogen. The plasmas used to form the antihydrogen fall into the very strongly magnetized regime, meaning that the gyrofrequency exceeds the plasma frequency and in the moderate Coulomb coupling regime denoting that the potential energy of interaction is on the order of the kinetic energy. The traditional Coulomb collision frequency is modified in these regimes.

A recent theoretical study has shown that the ion-electron temperature relaxation rate of a plasma in this strongly magnetized regime differs from the weakly magnetized regime and that the perpendicular and parallel relaxation rates are no longer equal. In many antimatter plasma experiments at ALPHA, the number density of antiprotons is much smaller than the number density of electrons. This high number density ratio justifies modeling the electrons as a heat bath on which the ions cool. In this scenario, the ion-electron and ion-ion relaxation rates will dominate. We aim to verify the theoretical ion-electron relaxation rates using molecular dynamics simulations. The Nose-Hoover thermostat is applied to the electrons to model them as a heat bath. To study only the effect of the ion-electron relaxation rate, the ion-ion interactions are ignored in the simulation. This work will validate recent theoretical findings on ion-electron temperature relaxation rates that may be studied in in future antimatter plasma experiments in the strongly magnetized regime.