Particle Acceleration during Collisionless Magnetic Reconnection

磁重联是自然界重要现象的基本过程，包括太阳耀斑、磁层亚暴和实验室聚变实验的中断。经典电阻率不足以解释在重联过程中观察到的粒子的能量。最近的一项重要发现是，对于给定的一组等离子体参数，重联可以以两种不同的模式进行：一种称为斯威特-帕克重联的慢模式，以及一种涉及霍尔效应产生的电场和磁场的快速模式。这两种模式之间的灾难性转变可以解释太阳日冕和实验室重联实验等电阻系统中快速重联的突然发生。该项目将研究磁x线附近重联区域的结构，并确定该结构与磁重联速率的关系。它将专注于发展一种新的粒子加热模型，在这种模型中，电子在收缩的磁岛中循环，经历类似费米的加速。该模型将电子获得的能量与重联过程中释放的磁能联系起来。离子的热速度通常与阿尔芬速度相当或远小于阿尔芬速度，它们的速度太慢，无法经历费米反射，必须调用一些其他过程来解释它们的能量。本项目将探索一种种子机制，在该机制中，进入重连排气的超阿尔芬离子就像拾取粒子一样，获得与排气速度相等的热能。动力学粒子，霍尔磁流体动力学（MHD）和测试粒子模拟将用于解决重连接过程中与电子和离子加速相关的关键问题。将继续与从事实验室重联实验的科学家合作，并与卫星数据合作，以观测结果作为理论预测的基准。对重联动力学的探索，特别是对高能粒子谱预测能力的发展，对于评估宇航员和我国天基技术资产的安全具有广泛的重要性。本科学生积极参与该项目的研究，并对女研究生的支持将进一步促进国家科学基金的教育目标。

Magnetic reconnection is a fundamental process underlying important phenomena in nature, including solar flares, magnetospheric substorms and disruptions in laboratory fusion experiments. Classical resistivity is not adequate to explain the observed energization of particles during reconnection events. An important recent discovery is that for a given set of plasma parameters, reconnection can proceed in two distinct modes: a slow mode known as Sweet-Parker reconnection, and a fast mode that involves electric and magnetic fields produced by the Hall effect. The catastrophic transition between these two modes can explain the sudden onset of fast reconnection in resistive systems such as the solar corona and laboratory reconnection experiments. This project will examine the structure of the reconnection region near the magnetic x-line and determine how the structure is related to the rate of magnetic reconnection. It will focus on the development of a new model of particle heating in which electrons circulating in contracting magnetic islands undergo Fermi-like acceleration. The model will link the energy gain by electrons to the magnetic energy released during reconnection. Ions, whose thermal speeds are typically comparable to or much smaller than the Alfven speed, are too slow to undergo Fermi reflection and some other process must be invoked to explain their energization. This project will explore a seed mechanism in which super-Alfvenic ions entering in reconnection exhausts act like pickup particles and gain a thermal energy equal to the exhaust velocity. Kinetic particle, Hall magnetohydrodynamic (MHD) and test particle simulations will be used to address the key issues related to electron and ion acceleration during reconnection. Collaborations will be continued with scientists working on laboratory reconnection experiments and with satellite data to benchmark the theoretical predictions with observations. 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 country's space-based technological assets. The active involvement of undergraduate students in research under this program and support for female graduate students will further the educational goals of NSF.