Reconnection and small-scale fields in 2D-3V hybrid-kinetic driven turbulence simulations

Abstract

The understanding of the fundamental properties of turbulence in collisionless plasmas, such as the solar wind, is a frontier problem in plasma physics. In particular, the occurrence of magnetic reconnection in turbulent plasmas and its interplay with a fully-developed turbulent state is still a matter of great debate. Here we investigate the properties of small-scale electromagnetic fluctuations and the role of fast magnetic reconnection in the development of a quasi-steady turbulent state by means of 2D-3V high-resolution Vlasov-Maxwell simulations. At the largest scales turbulence is fed by external random forcing. We show that large-scale turbulent motions establish a -5 3 spectrum at < k d 1 i and, at the same time, feed the formation of current sheets where magnetic reconnection occurs. As a result coherent magnetic structures are generated which, together with the rise of the associated small-scale non-ideal electric field, mediate the transition between the inertial and the subproton-scale spectrum. A mechanism that boosts the magnetic reconnection process is identified, making the generation of coherent structures rapid enough to be competitive with wave mode interactions and leading to the formation of a fully-developed turbulent spectrum across the so-called ion break.

Fully Kinetic Simulation of 3D Kinetic Alfvén Turbulence

“…Our work has important implications for the fundamental understanding of kinetic turbulence in weakly collisional plasmas, such as the solar wind, where a number of experimental studies already support the KAW turbulence scenario [20,27,29,31]. Several alternatives or extensions of the KAW turbulence theory have been considered, such as a transition to whistler turbulence deep in the subion range [17,18], or reconnection-mediated kinetic turbulence [84][85][86][87]. Given that our simulation covers only a moderate range of scales, it is presently difficult to assess the hypothetical role of these features and a definitive answer is left for future works.…”

Plasma turbulence at ion scales: a comparison between particle in cell and Eulerian hybrid-kinetic approaches

“…Despite the different early evolution, it can be noted that once the turbulent cascade is fully developed, the two sets of simulations exhibit the same qualitative behavior, for all the three beta cases, for what concerns the small-scale magnetic structures. In particular, all simulations exhibit reconnection occurring around the ion scales, leading to the formation of several small-scale island-like structures and to the full development of turbulence (see, e.g., Cerri & Califano 2017). These features can be indeed relevant in the context of the problem of turbulent dissipation in the solar wind as, for instance, the so-called "Turbulent Dissipation Challenge" (Parashar et al 2015), where many observations have been focusing on the nature of magnetic fluctuations around the ion characteristic scales (see, e.g., Roberts et al 2016;Lion et al 2016;Perrone et al 2016, and references therein).…”

Energy conversion in turbulent weakly collisional plasmas: Eulerian hybrid Vlasov-Maxwell simulations

“…Some examples are the dissipation of particular wave-modes, such as kinetic Alfvén 15,16 and whistler waves 17,18 , and the heating related -directly or indirectlyto magnetic reconnection [19][20][21][22][23][24] . Magnetic reconnection in a) Electronic mail: oreste.pezzi@gssi.it particular play a decisive role in energizing particles and dissipating energy in turbulent plasmas 25 .…”