The Dynamic Onset of Magnetic Reconnection

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Plasma is the most common form of matter found in the visible universe. Plasmas occurring in space and in astrophysical environments, as well as in laboratories on Earth, often carry magnetic fields. The interaction of the plasma with the magnetic field that pervades it is highly nonlinear and complex: the magnetic field affects the plasma dynamics and, conversely, the plasma can change the magnetic field. One of the most spectacular examples of such interaction is the process of magnetic reconnection: a plasma-driven reconfiguration of the magnetic field that threads it, which results in an explosive release of energy. The most popular manifestation of this phenomenon are solar flares; but reconnection occurs ubiquitously throughout the universe. The goal of this research is to advance the understanding of how the process of reconnection is triggered in a magnetized plasma; by doing so, it will contribute to the goals of NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics" Big Idea.Magnetic reconnection is a two-step process: an initial, slow stage of energy build-up and current-sheet formation, followed by the sudden, often explosive stage of energy release. Reconnection studies largely tend to focus on the latter, driven by attempts to solve the critically important problems of reconnection rate and energy partition. In this regard, a prominent feature of the last decade of reconnection research has been the plasmoid instability, whose key role in addressing those questions is now widely appreciated. However, the existence of this, and other, current sheet instabilities implies that the onset and the energy release stages cannot be trivially decoupled, since such instabilities set specific conditions on the parameters of the current sheets that are physically realizable; for example, a system-size Sweet-Parker current sheet in large systems can never dynamically arise because a tearing instability will inevitably disrupt the forming sheet much before it attains the Sweet-Parker ratio. The aim of this research is to develop the theoretical (analytical and numerical) understanding of the conditions imposed on the energy release stage by the build-up stage, thus paving the route for self-consistent studies of magnetic reconnection.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.