Kinetic Range of Strong Electric Field Turbulence Associated with Magnetotail Reconnection

The relaxation of many physical systems is constrained by collisions. However, most space and astrophysical plasmas are nearly collisionless, leaving open questions about the pathways of energy transfer and dissipation. In many turbulent plasmas, the electric field takes on the role of energy transfer leading to dissipation. Using measurements from the Magnetospheric Multiscale Mission, we study the statistical properties of the electric field spectrum in the kinetic range of strong turbulence generated by magnetic reconnection in the Earth's magnetotail. From the inertial to the kinetic range (often called the dissipation range) of scales, we find that turbulent fluctuations develop increasingly non-Gaussian features. The kinetic range contains two regimes with distinct behaviors in the power spectrum and measures of non-Gaussianity. In the subelectron kinetic regime (smaller than the electron gyroradius), the turbulence becomes isotropic and exhibits energy equipartition between the electric field and magnetic field. Our analyses indicate (1) a growing presence of intermittent structures that are expected to lead to enhanced energy dissipation, (2) changes in the electric field dynamics at the transitions between turbulence regimes, and (3) an asymptotic relaxation to a state of energy equipartition in the electromagnetic field in the subelectron kinetic range, where the energy transfer between the magnetic and electric fields appears to be near complete. These results reveal the importance of the electric field in mediating turbulence dissipation and relaxation in collisionless plasmas.