Snow Ben, Hillier Andrew S
University of Exeter, Exeter, EX4 4QF, UK.
Philos Trans A Math Phys Eng Sci. 2024 Jun 9;382(2272):20230227. doi: 10.1098/rsta.2023.0227. Epub 2024 Apr 25.
Turbulence is a fundamental process that drives mixing and energy redistribution across a wide range of astrophysical systems. For warm ([Formula: see text]) plasma, the material is partially ionized, consisting of both ionized and neutral species. The interactions between ionized and neutral species are thought to play a key role in heating (or cooling) of partially ionized plasmas. Here, mixing is studied in a two-fluid partially ionized plasma undergoing the shear-driven Kelvin-Helmholtz instability to evaluate the thermal processes within the mixing layer. Two-dimensional numerical simulations are performed using the open-source (PIP) code that solves for a two-fluid plasma consisting of a charge-neutral plasma and multiple excited states of neutral hydrogen. Both collisional and radiative ionization and recombination are included. In the mixing layer, a complex array of ionization and recombination processes occur as the cooler layer joins the hotter layer, and vice versa. In localized areas of the mixing layer, the temperature exceeds the initial temperatures of either layer with heating dominated by collisional recombinations over turbulent dissipation. The mixing layer is in approximate ionization-recombination equilibrium, however the obtained equilibrium is different to the Saha-Boltzmann local thermal equilibrium. The dynamic mixing processes may be important in determining the ionization states, and with that intensities of spectral lines, of observed mixing layers. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.
湍流是一个基本过程，它驱动着广泛天体物理系统中的混合和能量重新分布。对于温暖的（[公式：见原文]）等离子体，物质是部分电离的，由电离和中性成分组成。电离和中性成分之间的相互作用被认为在部分电离等离子体的加热（或冷却）中起关键作用。在此，研究了在经历剪切驱动的开尔文 - 亥姆霍兹不稳定性的双流体部分电离等离子体中的混合，以评估混合层内的热过程。使用开源的（PIP）代码进行二维数值模拟，该代码求解由电荷中性等离子体和中性氢的多个激发态组成的双流体等离子体。碰撞电离和辐射电离以及复合都被包括在内。在混合层中，当较冷的层与较热的层结合时，会发生一系列复杂的电离和复合过程，反之亦然。在混合层的局部区域，温度超过了任何一层的初始温度，加热主要由碰撞复合主导，超过了湍流耗散。混合层处于近似的电离 - 复合平衡状态，然而所获得的平衡与萨哈 - 玻尔兹曼局部热平衡不同。动态混合过程在确定观测到的混合层的电离状态以及光谱线强度方面可能很重要。本文是主题为“太阳大气的部分电离等离子体：最新进展和未来途径”的一部分。
