Thin Ionization Layer of the Enhanced Aurora

近一半的时间，极光会呈现出薄而明亮的层，称为“增强极光”。这些显示与 E 区中薄而密的重离子层有关。当波粒相互作用将环境电子加热到等于或略高于双原子氮的 17 eV 电离能时，就会产生这种现象。有几种可能的等离子体不稳定性可能会在薄层中产生超热电子，但尚未对薄电离层中的不稳定性如何发展进行详细的理论研究。该项目将研究薄而密的重离子层中出现的不稳定性。它将使用广泛的分析分析与粒子模拟相结合。对交叉场电流不稳定性的初步分析发现，重离子层中存在强烈的不稳定。初始静电模拟表明，当通电等于或高于氮电离能时，周围电子会发生大量加热。该模型的进一步改进将使用包括地面光学、雷达测量和现场火箭测量在内的各种数据，与观测结果进行精确比较。该模型还将用于检查其他竞争不稳定性，以便建立增强极光的机制。该提案中描述的理论工作和模拟代码也可能适用于与聚变装置中的杂质相关的不稳定性，其中已知来自壁和限制材料的重离子物质会污染核心氢等离子体。

Nearly half of the time, auroral displays exhibit thin, bright layers known as "enhanced aurora." These displays are associated with thin, dense, heavy ion layers in the E-region. They result when wave-particle interactions heat ambient electrons to energies at or just above the 17 eV ionization energy of diatomic nitrogen. There are several possible plasma instabilities that could produce suprathermal electrons in thin layers, but there has been no detailed theoretical investigation of how instabilities in the thin ionization layers develop. This project will examine instabilities which would occur in thin, dense, heavy ion layers. It will use extensive analytical analysis combined with particle simulations. A preliminary analysis of a cross field current instability has been found to be strongly unstable in the heavy ion layers. Initial electrostatic simulations show that substantial heating of the ambient electrons occurs with energization at or above the nitrogen ionization energy. Further improvements in the model will lead to precise comparisons with observations, using a variety of data including ground based optics, radar measurements, and in situ rocket measurements. The model will also be used to examine other competing instabilities, so that the mechanism for the enhanced aurora can be established. The theoretical work and simulation code described in this proposal is also likely to have applications to instabilities associated with impurities in fusion devices where heavy ion species originating from the wall and limiter materials are known to contaminate the core hydrogen plasma.