Self-Generated Coronal Magnetic Fields in High Energy Density Plasmas

该奖项支持一项关于磁场如何在天体物理和实验室等离子体中产生的计算研究，这些等离子体是许多带电粒子相互作用的集合。 磁场对等离子体的影响是众所周知的，但不同类型等离子体中磁场自生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，并决定了这些系统的演化，22年的太阳磁活动周期就是许多例子之一。激光驱动等离子体中的自生磁场也可以足够强以显著地改变等离子体行为。该项目将有助于解释气体星云中的恒星或实验室中的激光照射等离子体产生磁场的过程。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，阿尔马和JWST等当前和未来天文观测站对气体星云形态的观测将受益于该项目所发展的理论的发展和检验，该项目的目标是确定受辐照等离子体在不稳定性下自生磁场的主要机制。辐照等离子体中的自生磁场通常由比尔曼电池效应产生。磁场也可以由辐射驱动等离子体中的瑞利-泰勒（RT）不稳定性驱动。RT诱导场被能斯特流限制在消融前沿附近，不影响日冕等离子体性质。然而，在实验室等离子体激光照射，强B场已被观察到在日冕等离子体中使用质子射线照相术，除了标准的比尔曼电池领域周围的激光点。有人推测，磁热不稳定性（MTI）是在激光驱动的等离子体的日冕中的兆高斯磁场的主要来源，然而，最近的工作表明，传统形式的MTI被超音速等离子体流抑制。 这留下了一个重要的悬而未决的问题，即是什么导致了在实验室环境中观察到的日冕磁场。该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结果，包括电热不稳定性和流速等于能斯特速度的磁热不稳定性的新形式。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.