Protoplanetary discs are made of gas and dust orbiting a young star. They are also the birth place of planetary systems, which motivates a large amount of observational and theoretical research. In these lecture notes, I present a review of the magnetic mechanisms applied to the outer regions ( $R\gtrsim 1\ \mathrm {AU}$ ) of these discs, which are the planet-formation regions. In contrast to usual astrophysical plasmas, the gas in these regions is noticeably cold ( $T < 300\ \mathrm {K}$ ) and dense, which implies a very low ionisation fraction close to the disc midplane. In these notes, I deliberately ignore the innermost $(R\sim 0.1\ \mathrm {AU})$ region, which is influenced by the star–disc interaction and various radiative effects. I start by presenting a short overview of the observational evidence for the dynamics of these objects. I then introduce the methods and approximations used to model these plasmas, including non-ideal magnetohydrodynamics, and the uncertainties associated with this approach. In this framework, I explain how the global dynamics of these discs is modelled, and I present a stability analysis of this plasma in the local approximation, introducing the non-ideal magneto-rotational instability. Following this mostly analytical part, I discuss numerical models that have been used to describe the saturation mechanisms of this instability, and the formation of large-scale structures by various saturation mechanisms. Finally, I show that local numerical models are insufficient because magnetised winds are also emitted from the surface of these objects. After a short introduction on wind physics, I present global models of protoplanetary discs, including both a large-scale wind and the non-ideal dynamics of the disc.

中文翻译：

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原行星盘的磁流体动力学

原行星盘由围绕年轻恒星运行的气体和尘埃组成。它们也是行星系统的诞生地，激发了大量的观测和理论研究。在这些讲义中，我回顾了应用于外部区域的磁机制（ $R\gtrsim 1\ \mathrm {AU}$ ) 的这些圆盘，它们是行星形成区域。与通常的天体物理等离子体相比，这些区域的气体明显冷（ $T < 300\ \mathrm {K}$ ) 和密集，这意味着靠近圆盘中平面的电离分数非常低。在这些笔记中，我故意忽略了最里面的 $(R\sim 0.1\\mathrm {AU})$ 该区域受星盘相互作用和各种辐射效应的影响。我首先简要概述这些物体动力学的观测证据。然后，我介绍了用于模拟这些等离子体的方法和近似值，包括非理想磁流体动力学，以及与这种方法相关的不确定性。在这个框架中，我解释了如何对这些圆盘的全局动力学进行建模，并在局部近似下对这种等离子体进行了稳定性分析，并引入了非理想磁旋转不稳定性。在这个主要是分析部分之后，我讨论了用于描述这种不稳定性的饱和机制的数值模型，以及各种饱和机制形成的大尺度结构。最后，我表明局部数值模型是不够的，因为磁化风也从这些物体的表面发出。在简要介绍了风物理学之后，我介绍了原行星圆盘的全球模型，包括大尺度风和圆盘的非理想动力学。