Electron and proton energization in relativistic plasma turbulence

Particle energization is a fundamental, but poorly understood, consequence of plasma turbulence in high-energy astrophysical systems such as black-hole accretion flows. To study this process, we use particle-in-cell simulations of driven turbulence in collisionless, relativistic electron-proton plasmas. We focus on temperatures between the electron and proton rest mass energies, where the plasma consists of sub-relativistic protons and ultra-relativistic electrons. In most of the explored parameter space, we find that protons are preferentially heated, sufficient to establish a two-temperature plasma. We characterize the electron-proton energy partition as a function of plasma parameters, finding that it can be well described as a simple function of the ratio of electron-to-proton characteristic gyroradii. Both particle species exhibit nonthermal acceleration that forms a power-law energy distribution, but the electron acceleration becomes inefficient as the temperature is decreased. Thus, protons generally have a more substantial nonthermal population. Our empirical results have important implications for the establishment of two-temperature plasmas in black-hole accretion flows.