Identification of coherent structures and energy dissipation in shear-driven turbulent plasma with multi-point measurements: from MMS to Helioswarm and beyond

How turbulent plasmas dissipate energy at small scales is an unresolved issue. Turbulent plasmas are full of coherent structures (e.g., current sheets, flux ropes, flow vortices) that are key sites for local energy transfer between electromagnetic energy and thermal and kinetic energies. Four-spacecraft observations allow us to identify such coherent structures in 3-D using linear gradient estimations without invoking Taylors hypothesis. Using MMS observations of shear-driven turbulence induced by Kelvin-Helmholtz instability, we identify regions of strong energy dissipation and associated coherent structures as well as mechanisms that are likely responsible for the energy dissipation. The coherent structures are identified using n-point measurements with n = 2 (MMS spacecraft pair) and n = 4 (MMS spacecraft tetrahedron). To qualitatively understand the energy conversion, we set up a PIC simulation using empirical conditions and statistically investigate local energy dissipation at coherent structures. In addition, we test a method for quadratic gradient estimations using 10-point measurements recently developed by Shen et al. (2021) in the PIC simulation using virtual probes. Roles of coherent structures on energy dissipation will be discussed based on the MMS and PIC results. Insights from the applications of Shens method will also be discussed with a particular focus on the Helioswarm mission. This work is partially supported by grant RTA6280002 from Thailand Science Research and Innovation.