Direct observation of ion cyclotron damping of turbulence in Earth's magnetosheath plasma*

The turbulence in space plasmas undergoes dissipation at the kinetic scales, where the turbulent fluctuations in the electromagnetic fields are on the order of ion-cyclotron motions and

smaller. An open question in space plasma turbulence is what dissipation processes are removing energy from the turbulent fluctuations and converting it to ion and electron energies. The rapid in-situ measurements of magnetic fields, electric fields, and ion and electron phase space densities by NASA’s Magnetetospheric Multiscale (MMS) mission enable us to observe which

dissipation processes are present and to which particles the energy is being transferred. In this work we have identified ion cyclotron waves embedded in a turbulent cascade when the MMS spacecraft were located in the Earth’s magnetosheath, and the subsequent dissipation of turbulent energy through ion cyclotron damping. Combined with a previous analysis of the same interval of data which showed the presence of electron Landau damping, we identify the dissipation of a large fraction of the turbulent energy into the ions and electrons. The turbulent cascade rate at a scale larger than that of the ion cyclotron motion is quantified and directly compared to the dissipation of this energy into the ions at the ion kinetic scale. Team acknowledgement: We would like to thank the MMS instrument teams for the quality and care in calibration of their data.