Particle Acceleration during Collisionless Magnetic Reconnection

无碰撞磁重联过程中的粒子加速

• 批准号: 1202330
• 负责人: James Drake
• 金额: $ 39万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1202330&HistoricalAwards=false
• 关键词: Particle; Acceleration; during; Collisionless; Magnetic

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.

磁重联是自然界重要现象的基础过程，包括太阳耀斑、磁层亚暴和实验室聚变实验中的破坏。虽然在理解自然界和实验室中看到的快速释放磁能的机制方面取得了很大进展，但电子和离子加热和加速的机制还没有得到很好的理解，并且是该研究资助扩展的重点。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，最近的临边事件表明，高能电子分量的压力接近磁场的压力。脉冲耀斑揭示了丰富的增强高质荷比高能离子相比，日冕值。磁尾的卫星观测表明，重联直接产生非常高能的电子，而通常与重联事件有关的小磁岛充满了高能电子。外日球层的终止激波不是异常宇宙射线的局部来源，这一发现为以下可能性提供了可能性：扇形日球层场的重联可能是这些高能粒子的来源。本研究计划的目标是了解磁重联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结果进行比较的模型。粒子在细胞和霍尔MHD模拟将用于解决有关的电子和离子加速在重联过程中的关键问题。具体来说，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）通过研究大规模二维多电流层系统中磁岛的发展和电子和离子加速，解决平行电场与电子费米加速的作用以及消防管和其他各向异性不稳定性的影响; 2）利用粒子加速和重联的PIC模型，对一个中等大小的三维电流层系统，分析了三维磁绳是如何相互作用和加速粒子的; 3）通过研究离子拾取行为和与引导场重联的非绝热性，包括多个离子种类的相对加速率，了解脉冲耀斑中的丰度增强; 4）利用前三项研究的结果，建立一个重联过程中电子和离子加速的福克-普朗克模型，预测高能电子和离子的光谱，与观测结果进行比较。这项工作将与从事实验室重连实验的科学家合作进行，并利用卫星数据对理论预测与观测进行基准测试。 磁场重联是空间天气的驱动因素，也是对卫星的威胁。探索重连动力学，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们各国的天基技术资产具有广泛的重要性。本科生积极参与该方案下的研究，并支持女研究生，这将进一步推动国家科学基金会的广泛教育目标。