Heating of Magnetically Dominated Plasma by Alfv\'en-Wave Turbulence

Magnetic energy around astrophysical compact objects can strongly dominate over plasma rest mass. Emission observed from these systems may be fed by dissipation of Alfv\'en wave turbulence, which cascades to small damping scales, energizing the plasma. We use 3D kinetic simulations to investigate this process. When the cascade is excited naturally, by colliding large-scale Alfv\'en waves, we observe quasithermal heating with no nonthermal particle acceleration. We also find that the particles are energized along the magnetic field lines and so are poor producers of synchrotron radiation. At low plasma densities, our simulations show the transition to "charge-starved" cascades, with a distinct damping mechanism.