Self-Generated Coronal Magnetic Fields in High Energy Density Plasmas

该奖项支持一项关于如何在天体物理和实验室等离子体中产生磁场的计算研究，等离子体是许多相互作用的带电粒子的集合。众所周知，磁场可以强烈地影响等离子体的行为，但不同类型的等离子体中自产生磁场的机制仍然是一个谜。自生磁场在许多天体物理环境中无处不在，并决定着这类系统的演化，磁活动的22年太阳周期就是许多例子之一。激光驱动的等离子体中自产生的磁场也可以强大到足以显著改变等离子体的行为。这个项目将有助于解释在气体星云中的恒星或实验室中的激光照射的等离子体中产生磁场的过程。它还将有助于更好地理解实验室和天体物理等离子体系统中的热力学输运性质。例如，从ALMA和JWST等现有和未来的天文观测站对气体星云形态的观测将受益于该项目中发展的理论的发展和测试。该项目的目标是确定受不稳定性影响的辐照等离子体中自产生磁场的主要机制。辐照等离子体中的自生磁场通常是由比尔曼电池效应产生的。辐射驱动等离子体中的瑞利-泰勒(RT)不稳定性也可以驱动磁场。RT感应场被能斯特流限制在烧蚀前沿附近，并不影响日冕等离子体的性质。然而，在激光照射的实验室等离子体中，除了激光光斑周围的标准比尔曼电池场外，还使用质子照相技术在日冕等离子体中观察到了强B场。据推测，磁热不稳定性(MTI)是激光驱动等离子体日冕中产生超高斯磁场的主要来源；然而，最近的研究表明，传统形式的MTI被超音速等离子体流抑制。这就留下了一个重要的悬而未决的问题，那就是是什么导致了在实验室中观察到的日冕磁场。这个项目将研究新的不稳定机制，这些机制可以产生足够强的磁场来解释观测，包括电热不稳定和新形式的磁热不稳定，这些不稳定发生在流动速度等于能斯特速度的地方。这项工作将涉及理论分析和数值模拟。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。

This award supports a computational study of how magnetic fields can be generated in astrophysical and laboratory plasmas, which are collections of many electrically charged particles interacting with each other. It is well known that magnetic fields can strongly impact how plasmas behave, but the mechanisms for self-generation of magnetic field in different types of plasma continue to be a mystery. Self-generated magnetic fields are ubiquitous in many astrophysical environments and determine the evolution of such systems, with the 22-year solar cycle of magnetic activity being one of many examples. Self-generated magnetic fields in laser-driven plasmas can also be strong enough to significantly modify the plasma behavior. This project will help explain the processes giving rise to magnetic fields in plasmas irradiated by stars in gas nebulae or by lasers in the laboratory. It will also aid in better understanding thermodynamic transport properties in laboratory and astrophysical plasma systems. For example, observations of gas nebulae morphologies from current and future astronomical observatories, such as ALMA and JWST, stand to benefit from the development and testing of the theory developed in this project.The goal of this project is to identify the main mechanisms by which magnetic fields are self-generated in irradiated plasmas subject to instabilities. Self-generated magnetic fields in irradiated plasmas are often produced by the Biermann battery effect. Magnetic fields can also be driven by the Rayleigh-Taylor (RT) instability in radiation-driven plasmas. RT induced fields are confined near the ablation front by the Nernst flow and do not affect the coronal plasma properties. However, in laboratory plasmas irradiated by a laser, strong B-fields have been observed in the coronal plasma using proton radiography, in addition to the standard Biermann battery fields surrounding the laser spot. It has been speculated that the magneto-thermal instability (MTI) is the main source of mega-gauss magnetic fields in the corona of laser-driven plasmas; yet, recent work has shown that the traditional form of MTI is suppressed by supersonic plasma flows. This leaves an important open question on what is responsible for the coronal magnetic fields observed in laboratory settings. This project will investigate new instability mechanisms which can generate magnetic fields that are sufficiently strong to explain observations, including the electro-thermal instability and new forms of the magneto thermal instability localized where the flow velocity equals the Nernst velocity. The work will involve theoretical analysis and numerical simulations.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.