Diagnosing collisionless energy transfer using field-particle correlations: Alfven-Ion Cyclotron Turbulence

Abstract: We apply field-particle correlations -- a technique that tracks the time-averaged velocity-space structure of the energy density transfer rate between electromagnetic fields and plasma particles -- to data drawn from a hybrid Vlasov-Maxwell simulation of Alfv\'en Ion-Cyclotron turbulence. Energy transfer in this system is expected to include both Landau and cyclotron wave-particle resonances, unlike previous systems to which the field-particle correlation technique has been applied. In this simulation, the energy transfer rate mediated by the parallel electric field $E_\parallel$ comprises approximately $60\%$ of the total rate, with the remainder mediated by the perpendicular electric field $E_\perp$. The parallel electric field resonantly couples to protons, with the canonical bipolar velocity-space signature of Landau damping identified at many points throughout the simulation. The energy transfer mediated by $E_\perp$ preferentially couples to particles with $v_{tp} \lesssim v_\perp \lesssim 3 v_{tp}$ in agreement with the expected formation of a cyclotron diffusion plateau. Our results demonstrate clearly that the field-particle correlation technique can distinguish distinct channels of energy transfer using single-point measurements, even at points in which multiple channels act simultaneously, and can be used to determine quantitatively the rates of particle energization in each channel.