Unraveling the Runaway Electron Distribution Emitted by Lightning and Laboratory Discharges

解开闪电和实验室放电发射的失控电子分布

• 批准号: 1917069
• 负责人: Caitano da Silva
• 金额: $ 34.4万
• 依托单位: New Mexico Institute of Mining and Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1917069&HistoricalAwards=false
• 关键词: Unraveling; Runaway; Electron; Distribution; Emitted

One of the most fascinating discoveries in atmospheric physics is that thunderstorms may work as particle accelerators, producing intense fluxes of energetic radiation, which take different forms, such as: X-ray flashes emitted from the descending lightning channels, bursts of gamma rays observed at satellite altitudes known as terrestrial gamma-ray flashes (TGFs), and minute-long gamma-ray glows that terminate with a lightning bolt. All of these phenomena are different manifestations of bremsstrahlung emissions of the so-called runaway electrons, which are accelerated to high energies despite the collisions with air molecules. It is theoretically plausible that electron acceleration up to runaway energies (via the so-called thermal runaway electron mechanism) can happen at the tips of lightning channels where strong electric fields exist, but a number of questions about the detailed physics and its implications have puzzled researchers in recent years. Although the key role of runaway electrons in atmospheric electricity has been recognized, to date it remains unsettled whether runaway electrons influence the propagation of lightning and laboratory discharges. It also remains unclear if runaway electrons emitted by lightning leaders can seed TGFs. In some instances, X-ray emissions are observed on the ground and correlated to runaway electrons at the tips of descending lightning leader channels. But in some other occasions, powerful ground TGFs are detected instead. It remains a mystery what kind of lightning discharges produces the more energetic gamma emissions (instead of X-rays) and whether the mechanism involves thermal runaway electron generation. The main project goal is to address this knowledge gap with a robust methodology to infer the flux and spectral energy distribution of runaway electrons emitted by lightning and laboratory discharges. This is a 3-step approach that involves: (1) measuring X-ray emissions from short laboratory discharges that efficiently produce runaway electrons, are repeatable, and the electrical properties can be controlled; (2) developing scalable Monte Carlo simulation codes that can unveil the flux and spectral distribution of runaway electrons when driven/validated by the rich dataset collected in step (1); and (3) performing X-ray observations at the Langmuir laboratory mountain-top facility, leveraging the knowledge acquired from steps (1)-(2) to infer the properties of runaway electrons emitted by natural lightning. Additionally, the project has also an educational aim - the research team will develop a freshman-level classroom module to teach basic concepts of electrical breakdown in air via demonstrations with electrical discharges.This project is jointly funded by NSF Physical and Dynamic Meteorology program and the Established Program to Stimulate Competitive Research (EPSCoR).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.

大气物理学中最令人着迷的发现之一是，雷暴可以充当粒子加速器，产生强烈的高能辐射通量，其形式多种多样，例如：从下降的闪电通道发出的 X 射线闪光、在卫星高度称为地面伽马射线闪光（TGF），以及以闪电结束的一分钟长的伽马射线辉光。所有这些现象都是所谓失控电子轫致辐射的不同表现，尽管与空气分子碰撞，但电子仍被加速到高能。从理论上讲，电子加速到失控能量（通过所谓的热失控电子机制）可能发生在存在强电场的闪电通道的尖端，但有关详细物理及其含义的许多问题令人困惑近年来的研究人员。尽管人们已经认识到失控电子在大气电中的关键作用，但迄今为止，失控电子是否影响闪电和实验室放电的传播仍悬而未决。目前还不清楚闪电先导发射的失控电子是否可以产生 TGF。在某些情况下，在地面上观察到 X 射线发射，并与下降闪电先导通道尖端的失控电子相关。但在其他一些情况下，却检测到了强大的地面 TGF。什么样的闪电放电会产生能量更高的伽马射线（而不是 X 射线）以及该机制是否涉及热失控电子的产生，仍然是一个谜。主要项目目标是通过强大的方法来解决这一知识差距，以推断闪电和实验室放电发射的失控电子的通量和光谱能量分布。这是一个三步方法，包括：(1) 测量实验室短暂放电产生的 X 射线发射，该放电可有效产生失控电子，可重复且电特性可控制； （2）开发可扩展的蒙特卡罗模拟代码，当由步骤（1）中收集的丰富数据集驱动/验证时，可以揭示失控电子的通量和光谱分布； (3) 在 Langmuir 实验室山顶设施进行 X 射线观测，利用从步骤 (1)-(2) 获得的知识来推断自然闪电发射的失控电子的特性。此外，该项目还有一个教育目标——研究团队将开发一个新生水平的课堂模块，通过放电演示来教授空气中电击穿的基本概念。该项目由美国国家科学基金会物理和动态气象学项目和美国国家科学基金会联合资助制定刺激竞争性研究计划 (EPSCoR)。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Production of runaway electrons and x-rays during streamer inception phase

流注起始阶段产生失控电子和 X 射线

• DOI: 10.1088/1361-6463/acaab9
• 发表时间: 2022-12-12
• 期刊: Journal of Physics D: Applied Physics
• 作者: L. Contreras;C. Silva;R. Sonnenfeld
• 通讯作者: R. Sonnenfeld

Data-Driven Simulations of the Lightning Return Stroke Channel Properties

雷电回击通道特性的数据驱动模拟

• DOI: 10.1109/temc.2022.3189590
• 发表时间: 2022-07
• 期刊: IEEE Transactions on Electromagnetic Compatibility
• 影响因子: 2.1
• 作者: Taylor, Michael C.;da Silva, Caitano L.;Walker, T. Daniel;Christian, Hugh J.
• 通讯作者: Christian, Hugh J.

Dart‐Leader and K‐Leader Velocity From Initiation Site to Termination Time‐Resolved With 3D Interferometry

Dart — 先导和 K — 从起始位置到终止时间的先导速度 — 通过 3D 干涉测量法解析

• DOI: 10.1029/2020jd034309
• 发表时间: 2021-05
• 期刊: Journal of Geophysical Research: Atmospheres
• 作者: Jensen, Daniel P.;Sonnenfeld, Richard G.;Stanley, Mark A.;Edens, Harald E.;da Silva, Caitano L.;Krehbiel, Paul R.
• 通讯作者: Krehbiel, Paul R.

Relationship Between Sprite Current and Morphology

精灵电流与形态的关系

• DOI: 10.1029/2020ja028930
• 发表时间: 2021-02-15
• 期刊: Journal of Geophysical Research: Space Physics
• 作者: L. Contreras;R. Sonnenfeld;C. D. da Silva;M. McHarg;D. Jensen;J. Harley;L. M. Taylor;R. Haal;H. Stenbaek
• 通讯作者: H. Stenbaek

Electrostatic Conditions That Produce Fast Breakdown in Thunderstorms

在雷暴中产生快速击穿的静电条件

• DOI: 10.1029/2021jd034829
• 发表时间: 2021-09
• 期刊: Journal of Geophysical Research: Atmospheres
• 作者: Attanasio, Ale;da Silva, Caitano;Krehbiel, Paul
• 通讯作者: Krehbiel, Paul