The Dynamic Onset of Magnetic Reconnection

等离子体是可见宇宙中最常见的物质形式。在太空和天体物理环境中以及在地球上的实验室中出现的等离子体通常带有磁场。等离子体与其周围磁场的相互作用是高度非线性和复杂的：磁场会影响等离子体的动力学，反过来，等离子体也会改变磁场。这种相互作用最壮观的例子之一是磁重联过程：由等离子体驱动的磁场的重新配置，导致能量的爆炸性释放。这种现象最常见的表现形式是太阳耀斑，但宇宙中到处都有重新连接的现象。这项研究的目的是促进人们对磁化等离子体中如何触发重联过程的理解；通过这样做，它将有助于美国国家科学基金会“宇宙之窗：多信使天体物理学时代”的大理想的目标。磁重联是一个两步过程：能量积累和电流片形成的初始、缓慢阶段，随后是突然的、通常是爆炸性的能量释放阶段。重联研究在很大程度上倾向于关注后者，原因是试图解决重联速率和能量分配这两个至关重要的问题。在这方面，过去十年重新连接研究的一个突出特点是等离子体不稳定，它在解决这些问题方面的关键作用现在得到了广泛的赞赏。然而，这种电流片不稳定性和其他电流片不稳定性的存在意味着起始阶段和能量释放阶段不能简单地分离，因为这种不稳定性对物理上可实现的电流片的参数设置了特定的条件；例如，大系统中系统大小的Sweet-Parker电流片永远不会动态出现，因为撕裂不稳定性将不可避免地在成形片达到Sweet-Parker比率之前破坏成形片。这项研究的目的是从理论上(分析和数值上)理解建立阶段对能量释放阶段施加的条件，从而为磁重联的自洽研究铺平道路。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.