Particle Acceleration during Collisionless Magnetic Reconnection

磁重联是自然界中重要现象的基本过程，这些现象包括太阳耀斑、磁层亚暴和实验室聚变实验的中断。虽然在理解自然界和实验室中看到的磁能快速释放的机制方面已经取得了很大进展，但电子和离子加热和加速的机制还没有得到很好的理解，这是这项研究拨款延期的重点。太阳耀斑观测表明，释放的大部分磁能以高能离子和电子的形式出现，最近的极端事件表明，高能电子成分的压力接近磁场的压力。与日冕值相比，脉冲耀斑揭示了高质量电荷比高能离子的丰度增强。对磁尾的卫星观测表明，重联直接产生非常高能的电子，经常与重联事件有关的小磁岛充满了高能电子。外部日光层的终止激波不是异常宇宙线的局部来源，这一发现表明，日球场的重新连接可能是这些高能粒子的来源。这个研究计划的目标是了解磁重新连接过程中电子和离子的加热和加速，并开发一个可以与航天器观测进行比较的模型。将使用细胞内粒子模拟和霍尔MHD模拟来解决与重新连接过程中的电子和离子加速有关的关键问题。具体地说，在他们以前工作的基础上，该团队将追求四个不同的科学目标：1)通过研究大规模2-D多电流层系统中的磁岛发展和电子和离子加速，解决平行电场对电子的费米加速的作用，以及火管和其他各向异性不稳定性的影响；2)使用中等大小的3-D电流层系统的重联和粒子加速的PIC模型，评估3-D磁通量绳如何相互作用和加速粒子；3)通过研究与引导场重联时的离子拾取行为和非绝热性，包括多离子物种的相对加速率，来了解脉冲耀斑中的丰度增强；4)利用前三项研究的结果，建立重联过程中电子和离子加速的Fokker-Planck模型，该模型预测高能电子和离子的光谱，以便与观测结果进行比较。这项工作将与从事实验室重新连接实验的科学家合作完成，并使用卫星数据将理论预测与观测进行基准比较。磁重联是空间天气的驱动因素，并由此对卫星构成威胁。探索重新连接的动态，特别是发展高能粒子谱的预测能力，对于评估宇航员的安全和我国的天基技术资产具有广泛的重要意义。本科生积极参与该计划下的研究，并支持女性研究生，将推动国家科学基金会的广泛教育目标。

Magnetic reconnection is a fundamental process underlying important phenomena in nature, including solar flares, magnetospheric substorms and disruptions in laboratory fusion experiments. While great progress has been made on understanding the mechanisms for the fast release of magnetic energy seen in nature and the laboratory, the mechanisms for electron and ion heating and acceleration are not as well understood and are the focus of the extension of this research grant. Solar flare observations suggest that a large fraction of the magnetic energy released appears in the form of energetic ions and electrons and recent over-the-limb events suggest that the pressure of the energetic electron component approaches that of the magnetic field. Impulsive flares reveal abundance enhancements of high mass-to-charge energetic ions compared with coronal values. Satellite observations in the magnetotail indicate that reconnection directly produces very energetic electrons and that the small magnetic islands that are often associated with reconnection events are filled with energetic electrons. The revelation that the termination shock in the outer heliosphere is not the local source of Anomalous Cosmic Rays leaves open the possibility that reconnection of the sectored heliospheric field may be the source of these energetic particles.The goal of this research program is to understand electron and ion heating and acceleration during magnetic reconnection and develop a model that can be compared with spacecraft observations. Particle-in-cell and Hall MHD simulations will be used to address key issues related to electron and ion acceleration during reconnection. Specifically, building on the results from their previous work, the team will pursue four distinct scientific objectives: 1) address the roles of parallel electric fields versus Fermi acceleration for electrons and the impact of firehose and other anisotropy instabilities through the study of magnetic island development and electron and ion acceleration in large-scale 2-D multi current layer systems; 2) asses how 3-D flux ropes interact and accelerate particles using a PIC model of reconnection and particle acceleration for a modest sized 3-D current layer system; 3) understand abundance enhancements in impulsive flares by studying ion pickup behavior and non-adiabaticity in reconnection with a guide field, including the relative acceleration rates of multiple ion species; 4) Use the results from the first three studies to develop a Fokker-Planck model of electron and ion acceleration during reconnection that predicts the spectra of energetic electrons and ions for comparison with observations. The work will be done in collaboration with scientists working on laboratory reconnection experiments and with satellite data to benchmark the theoretical predictions with observations. Magnetic reconnection is the driver of space weather and the resultant threat to satellites. The exploration of the dynamics of reconnection and particularly the development of a predictive capability for energetic particle spectra has broad importance for assessing both the safety of astronauts and our countries space-based technological assets. The active involvement of undergraduate students in research under this program and support for female graduate students will further the broad educational goals of NSF.