Thermal Runaway Breakdown of Air: A Possible Origin of Energetic Radiation Generated in the Earth's Atmosphere

空气的热失控分解：地球大气中产生的高能辐射的可能来源

• 批准号: 0741589
• 负责人: Victor Pasko
• 金额: $ 25.35万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-01 至 2012-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0741589&HistoricalAwards=false
• 关键词: Thermal; Runaway; Breakdown; Air; Possible

The Principal Investigator will theoretically investigate thermal runaway breakdown of air and the associated energetic radiation from X-rays to hard X-rays/lower-energy gamma rays. Energetic radiation originating in the Earth's atmosphere has been recently detected from both space and ground based platforms, and intensive research efforts have been carried out in order to investigate its origin. The X-ray and gamma ray emissions are believed to originate from interactions between high-energy electrons and atomic particles through bremsstrahlung. The only existing mechanism capable of explaining the generation of these high-energy electrons in air is electron runaway. This phenomenon is a result of a decreasing probability of electron interactions with atomic particles for electrons with energies in the range from about 100 eV to about 1 MeV. For a high-energy electron, it is possible that the electron gains more energy from an external electric field than it loses to collisions, and continues to accelerate to very high (1 MeV) energies. Thus far two scenarios of runaway breakdown have been proposed: runaway breakdown initiated by relativistic runaway electrons generated by cosmic rays, and initiated by thermal runaway electrons (cold electrons accelerated to high energies by extremely large electric fields). The initial research work to explain the observed X-ray and gamma ray emissions focused on studies of relativistic runaway electron avalanche and the resulting breakdown of air. However, recent studies show that relativistic runaway electron theory has difficulty in explaining some features of observations, for example, the spectrum of X-ray and gamma ray emissions and the correlation between the X-ray bursts with the stepping processes of lightning leaders. A critical condition for the occurrence of thermal runaway breakdown is an extremely large field sustained over a finite space during a relatively extended time period. This condition was a major obstacle for applying the thermal runaway breakdown to interpretation of the observed energetic emissions during early research work. However, recent progress in understanding of streamer discharges predicts possible realization of this condition during this type of discharge. It is the purpose of the research to investigate the runaway breakdown of air initiated by thermal runaway electrons and quantify the associated energetic emissions. Intellectual merit of the research is defined by the need to develop a theory to explain the energetic radiation originating in the Earth's atmosphere. To advance current understanding of thermal runaway breakdown of air and its induced energetic emissions, three outstanding scientific questions will be addressed: (1) What is the electric field configuration during a lightning leader stepping process? (2) How does the thermal runaway breakdown initiate and develop? What is the energy distribution of the resulting runaway electrons? (3) What are the emissions from the thermal runaway breakdown of air, and how do these emissions link to the recently-discovered X-ray and gamma-ray flashes associated with thunderstorm activity? The importance of addressing these questions is underscored by the need to understand the role of thermal runaway breakdown of air in the production of observed X-ray and gamma-ray emissions, and in the formation and propagation of lightning. This study is important for interpreting recent observations and experiments on lightning discharges, and for establishing of the exact physical mechanism of the energetic radiation originating from the Earth's atmosphere. Broader impacts of the research include: (1) the development of interdisciplinary research program involving studies relevant to both conventional and runaway breakdown theories, and energetic radiation generated in electron-atom interactions, (2) the education and training of a graduate student, (3) the support and further training of a post-doctoral scholar, (4) the involvement of undergraduate students in research activities during summertime periods, (5) the dissemination of results in the form of refereed publications and conference presentations.

理论上，主要研究者将研究空气的热失控崩溃以及从X射线到硬X射线/低能量伽玛射线的相关能量辐射。 最近从太空和地面平台中检测到了源自地球大气的能量辐射，并为了研究其起源而进行了密集的研究工作。 X射线和伽马射线的排放据信是源自通过Bremsstrahlung的高能电子和原子颗粒之间的相互作用。唯一能够解释这些高能电子在空气中产生的机制是电子失控。该现象是由于电子相互作用与原子颗粒的概率降低的结果，其能量在约100 eV到约1 meV的范围内。 对于高能电子，电子从外部电场中获得的能量可能比碰撞输掉的能量更多，并且继续加速到非常高（1 MeV）的能量。到目前为止，已经提出了两种失控分解的情况：由宇宙射线产生的相对论失控电子引发的失控崩溃，并由热失控电子（通过极大的电场加速到高能的冷电子）发起。最初的研究工作解释了观察到的X射线和伽马射线排放，重点是相对论失控电子雪崩的研究和空气的崩​​溃。然而，最近的研究表明，相对论的失控电子理论难以解释某些观测特征，例如，X射线和伽马射线的频谱以及X射线爆发之间的相关性与闪电领导者的逐步过程之间的相关性。发生热失去崩溃的临界条件是在相对较长的时间段内在有限空间上维持的一个极大的场。这种情况是将热失控分解应用于早期研究工作期间观察到的能量排放的解释的主要障碍。但是，了解流媒体排放的最新进展预测了这种情况下可能实现这种情况。研究的目的是研究热失控电子引发的空气的失控并量化相关的能量排放。研究的智力优点是由开发一种理论来解释源自地球大气层的能量辐射的必要性所定义的。为了促进当前对空气热失控及其诱导的能量排放的理解，将解决三个杰出的科学问题：（1）在雷电领导者步进过程中，电场配置是什么？ （2）热失控崩溃如何启动和发展？产生的失控电子的能量分布是什么？ （3）从空气的热失控崩溃中的排放是什么，这些排放如何与与雷暴活动相关的最近发现的X射线和伽马射线闪光灯联系在一起？解决这些问题的重要性强调了，需要了解空气中热失控的崩溃在观察到的X射线和伽马射线排放以及闪电的形成和传播中的作用。这项研究对于解释有关闪电放电的最新观察和实验至关重要，以及建立源自地球大气的能量辐射的确切物理机制。研究的更广泛的影响包括：（1）涉及与传统和失控的崩溃理论相关的研究以及电子互动中产生的充满活力的辐射的发展，（2）研究生的教育和培训，（3）在学业后的研究和进一步的培训，在学业后的研究中，（4）涉及研究生（4）涉及研究生（4），（4）被培训（4）纳入研究生（4）。结果以审查的出版物和会议演讲的形式。