Chen Zhiyuan, Wang Yibai, Tang Haibin, Ren Junxue, Li Min, Zhang Zhe, Cao Shuai, Cao Jinbin
School of Astronautics, Beihang University, Beijing 100083, China.
School of Space and Environment, Beihang University, Beijing 100083, China.
Phys Rev E. 2020 May;101(5-1):053208. doi: 10.1103/PhysRevE.101.053208.
Magnetic nozzles are convergent-divergent applied magnetic fields which are commonly used in electric propulsion, manufacturing, and material processing industries. This paper studies the previously overlooked physics in confining the thermalized ions injected from a near-uniform inlet in the magnetic nozzle. Through fully kinetic planar-3V particle-in-cell (PIC) modeling and simulation, an electric potential barrier is found on the periphery of the nozzle throat, which serves to confine the thermalized ions by the electric force. With the initial thermal energy as driving force and insufficient magnetic confinement, the ions overshoot the most divergent magnetic line, which results in the accumulation of positive space charges around the throat. The accumulated charges would create an ion-confining potential barrier with limited extent. Apart from the finite-electron Larmor radius (FELR) effect, two more factors are put forward to account for the limited extent of the potential barrier: the depletion of ion thermal energy and the short-circuiting effect. The influences of inlet temperature ratio of ions to electrons and magnetic inductive strength B_{0} are quantitively investigated using the PIC code. The results indicate that the potential barrier serves as a medium to transfer the gas dynamic thrust to the magnetic nozzle while providing constrain to the ions, like the solid wall in a de Laval nozzle. In high-B_{0} regime, the finite-ion Larmor radius (FILR) effect becomes dominant rather than the FELR effect in the plasma confinement of magnetic nozzles.
磁喷嘴是一种收敛-发散型外加磁场，常用于电推进、制造和材料加工行业。本文研究了磁喷嘴中从近均匀入口注入的热化离子受限过程中此前被忽视的物理现象。通过全动理学平面3V粒子模拟（PIC）建模与仿真，发现在喷嘴喉部周边存在一个电势垒，该电势垒通过电力来限制热化离子。以初始热能为驱动力且磁约束不足时，离子会越过最发散的磁力线，导致喉部周围正空间电荷的积累。积累的电荷会形成一个范围有限的离子约束电势垒。除了有限电子拉莫尔半径（FELR）效应外，还提出了另外两个因素来解释电势垒范围有限的原因：离子热能的耗尽和短路效应。使用PIC代码定量研究了离子与电子的入口温度比和磁感应强度B₀的影响。结果表明，电势垒就像拉瓦尔喷嘴中的固体壁一样，在为离子提供约束的同时，作为一种介质将气体动力推力传递给磁喷嘴。在高B₀状态下，有限离子拉莫尔半径（FILR）效应在磁喷嘴的等离子体约束中比FELR效应更占主导地位。
