Dependence of eddy diffusion coefficient on plasma parameter β in Earth’s magnetotail

The work analyzes dependences of eddy diffusion coefficients in the X, Y, and Z directions of the GSM coordinate system on the plasma parameter β, taking into account the distance from Earth, the direction of the interplanetary magnetic field, and conditions of geomagnetic activity in the magnetotail according to MMS mission data. These parameters are determined by root-mean-square velocities of ions and their autocorrelation time. Eddy diffusion coefficients characterize the magnitude of turbulent transport in the magnetotail and are the parameters of the model of turbulent plasma sheet. We have analyzed more than 20000 12-min intervals during which the MMS satellites were located within a region with plasma density more than 0.1 cm–3 and average ion energy more than 0.5 keV. It is shown that as the plasma parameter increases, the eddy diffusion coefficients increase as well. This increase stops at β~1. Analysis of the relative contribution of changes in root-mean-square velocity and autocorrelation time to the eddy diffusion coefficient has revealed that there is no significant dependence on autocorrelation time.