A New Technique for the Investigation of the Energy Cascade Associated with Coherent Structures in Kelvin-Helmoltz Turbulence

Abstract:

The dissipation of turbulent energy at small scales in space plasmas remains an open and challenging problem. Two plausible channels for energy dissipation have been intensively investigated in recent years: linear wave damping and non-linear interactions within coherent structures. However, a general consensus has not yet been reached on what is the relative importance of these two processes. It is now well established that coherent structures in the form of current sheets are associated with localized particle heating, and are generally responsible for the observed intermittent nature of plasma turbulence. Still, the contribution of such structures to the local energy spectrum is not well understood. Here we apply a 'space-filter' technique to a two-fluid plasma simulation of Kelvin-Helmoltz turbulence, in order to obtain a local measure of the inter-scale transfer and to characterize the contribution of coherent structures to the energy spectrum. Despite of being well-known in the hydrodynamics and Large-Eddy-Simulation communities, such technique is applied here for the first time to space plasma turbulence. Specifically, we study in detail the current sheets identified in turbulent Kelvin-Helmoltz vortexes by the Partial Variance of Increments (PVI) technique, and we discuss the correlation between the inter-scale transfer and high values of the PVI index.