Space Propulsion and Advanced Concepts Engineering (SPACE) Laboratory, University of Washington, Seattle, Washington 98015, USA.
Electric Propulsion and Plasma Dynamics Laboratory (EPPDyL), Princeton University, Princeton, New Jersey 08544, USA.
Phys Rev Lett. 2019 Oct 4;123(14):145001. doi: 10.1103/PhysRevLett.123.145001.
Electron demagnetization in a magnetically expanding plasma, a fundamental process for plasma flow and detachment in magnetic nozzles, is experimentally investigated using a rf plasma source and magnetic nozzle (MN). Measurements of the plasma potential spatial profile reveal an ion-confining potential surface, indicative of the edge of a magnetized plasma, that extends along the outermost magnetic flux surface. The downstream extent of the potential surface scales inversely with a characteristic electron Larmor radius, which agrees with an existing theory [E. Ahedo and M. Merino, Phys. Plasmas 19, 083501 (2012)PHPAEN1070-664X10.1063/1.4739791] for electron demagnetization via finite electron Larmor radius (FELR) effects. These results represent the first experimental evidence of FELR demagnetization, and provide an empirical metric for the significance of FELR effects based on the degree of separation between electron and magnetic flux surfaces. With this metric, a critical magnetic field strength is found that ensures electrons remain magnetized through the MN turning point, thus avoiding the rapid plume divergence associated with premature demagnetization.
在磁扩展等离子体中电子退磁，这是磁喷嘴中等离子体流动和脱离的基本过程，通过射频等离子体源和磁喷嘴 (MN) 进行了实验研究。等离子体电势空间分布的测量揭示了一个离子限制势面，这表明存在一个磁化等离子体的边缘，沿着最外层的磁通量表面延伸。势面的下游延伸与特征电子拉莫尔半径成反比，这与现有的电子退磁通过有限电子拉莫尔半径 (FELR) 效应的理论一致[E. Ahedo 和 M. Merino，Phys. Plasmas 19, 083501 (2012)PHPAEN1070-664X10.1063/1.4739791]。这些结果代表了 FELR 退磁的第一个实验证据，并提供了一种基于电子和磁通量表面分离程度的 FELR 效应重要性的经验度量。有了这个度量，可以找到一个临界磁场强度，以确保电子在 MN 转折点处保持磁化，从而避免与过早退磁相关的快速羽流发散。
