Time-dependent kinetic analysis of trapped electrons in a magnetically expanding plasma
Time-dependent kinetic analysis of trapped electrons in a magnetically expanding plasma
复制标题
磁膨胀等离子体中俘获电子的时间相关动力学分析
DOI：
10.1088/1361-6595/ab2c64
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发表时间：
2019
影响因子：
3.8
通讯作者：
Y. Hwang
中科院分区：
文献类型：
--
作者：
J. Kim;J. Jang;K. S. Chung;K. Chung;Y. Hwang
磁喷管（MN）作为推进器的加速级，其电子运动特性的深入研究对MN性能的提高具有重要意义。在这个意义上，电子动量到离子动能的转换决定了MN的特性，磁膨胀等离子体的动力学特征的基础研究集中在电子性质的空间分布和所需的应用提出了方向。与这种重要性的共同看法不同，各种研究小组提出了相互矛盾的论点，根据他们的理论方法，从电子热流的观点关于离子束加速。我们指出，喷嘴效率的提高缺乏理论共识的主要原因是由于缺乏明确的解释等离子体的性质，只专注于电子的最终状态。在这封信中，电子能量分布的时间分辨测量已经完成，以掌握详细的一系列膨胀过程。研究表明，自生电场逐渐形成的有效势阱对电子的运动起着限制作用，这种作用是由于电子能量分布的改变，表现为俘获电子的积累。在整个区域上的累积减小了系统的冷却速率的程度，并且减小了最初由绝热膨胀产生的下游区域中的电场。本研究强调，MN的动力学特征强烈影响的非稳态运动的被捕获的电子，因此，时间行为的被捕获的电子必须被考虑的喷嘴性能的预测和分析。
A deep understanding of the kinetic properties of the electrons in a magnetic nozzle (MN), which is attracting attention as an acceleration stage for thrusters, is of great significance as it directly contributes to the development of the MN performance. In the sense that a conversion of the electron momentum to the ion kinetic energy determines the characteristics of the MN, fundamental research on the kinetic feature of a magnetically expanding plasma has focused on the spatial distribution of the electron properties and proposed directions to the desired application. Unlike the common perception of this importance, various research groups have proposed contradictory arguments based on their theoretical approaches regarding the ion beam acceleration from the viewpoint of heat flow of electrons. We point out that the main reason for the absence of a theoretical consensus for the nozzle efficiency improvements arises from the lack of the clear interpretation of the plasma properties by focusing only on the final state of the electrons. In this Letter, time-resolved measurement of the electron energy distributions has been performed to grasp a detailed series of expansion processes. It has been revealed that the effective potential well gradually formed by the self-generated electric field acts as a limiting factor in the motion of electrons; this effect attributes to the changes of the electron energy distribution represented as the accumulation of the trapped electrons. The accumulation over the entire region diminishes the degree of the cooling rate of a system and decreases the electric field in the downstream region initially generated by the adiabatic expansion. The present study emphasizes that the kinetic features of an MN are strongly affected by the non-stationary motion of the trapped electrons; thus, the temporal behavior of the trapped electrons must be considered for prediction and analysis of nozzle performances.