Diagnosing collisionless energy transfer using field–particle correlations: Alfvén-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 Alfven-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 to comprises approximately 60% of the total rate, with the remainder mediated by the perpendicular electric field E-perpendicular to. 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-perpendicular to preferentially couples to particles with v(tp) less than or similar to v(perpendicular to) less than or similar to 3 v(tp), where vtp is the proton thermal speed, 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.