Direct Observation of Ion Cyclotron Damping of Turbulence in Earth's Magnetosheath Plasma

The turbulent cascade in heliospheric plasmas, such as the solar corona, solar wind, and Earth's magneotsheath, transfers energy to kinetic length scales at which poorly understood dissipation mechanisms damp the turbulent fluctuations and consequently energize the plasma particles. The dissipation mechanism in effect can be identified in the resulting velocity-space signature from applying the Field-Particle Correlation (FPC) technique. The FPC technique correlates the time series of the phase-space density measurements with that of the electric field fluctuations, both of which are measured by instrument suites aboard NASA's Magnetospheric Multiscale (MMS) mission. In a case study when the MMS spacecraft were located in the Earth's magnetosheath, we quantify the turbulent cascade rate in the inertial range and compare it to the dissipation of this energy at the ion kinetic scale through ion cyclotron damping, and at the electron kinetic scale through electron Landau damping. The distinct velocity-space signatures of these dissipation mechanisms allow us to differentiate between the two, as well as quantify the particle energization rate due to each. By comparing each species' energization rate with the turbulent cascade rate, we identify the dominant channel through which turbulent energy is dissipated.