The Effects of Ion Kinetic Instabilities on the Three-Dimensional Reconnection of Ion-Scale Current Sheets in the Solar Wind

Abstract:

Solar wind plasmas have been observed to host a population of magnetic discontinuities associated with turbulent fluctuations and solar atmospheric processes. These thin current sheets, which may be subject to a tearing instability, can heat the plasma and accelerate particles via magnetic reconnection, and indeed have observed correlations with energetic particles. Further correlations of observations of thin, ion-scale current sheets with local temperature anisotropies invite an exploration of the role of ion kinetic instabilities in their evolution and associated heating processes, particularly when coupled with a turbulent medium such as the solar wind. Recent work has demonstrated that proton temperature anisotropy plays an important role in the growth and evolution of the two-dimensional, collisionless tearing instability, for example via the growth of background ion cyclotron and fire hose instabilities. Here, we present results of a three-dimensional extension of this investigation using three-dimensional hybrid simulations of current sheets in Harris equilibrium. We demonstrate the emergence of persistent three-dimensional structures and instabilities which significantly alter the development of the tearing instability, including i) patchy reconnection sites formed by break up of initially two-dimensional x-lines, and ii) narrow-band kink of the current sheet in the current-carrying direction by the growth of a drift-kink instability. We discuss the relative growth rates of tearing and drift-kink instabilities for a range of background and current sheet temperature anisotropies and guide fields, quantify local ion heating, and present potential observational signatures. We also examine the character of turbulence generated by the interaction of multiple ion-scale current sheets in three-dimensions.