Shpilman Z, Gouzman I, Lempert G, Grossman E, Hoffman A
Space Environment Section, Soreq NRC, Yavne 81800, Israel.
Rev Sci Instrum. 2008 Feb;79(2 Pt 1):025106. doi: 10.1063/1.2885044.
The materials of spacecraft external surfaces in low Earth orbit (LEO) are exposed to the various constituents of the space environment, including atomic oxygen (AO) and solar ultra violet (UV) radiation. Material degradation and erosion by LEO are simulated in ground laboratories using a variety of experimental facilities, each with their respective limitations. rf oxygen plasma is a simulation facility widely used for materials screening for LEO application. However, the complex plasma environment, which contains, in addition to the neutral oxygen atoms, excited species, electrons, and ions as well as vacuum ultraviolet (VUV) radiation, might lead to erroneous determination of materials reactivity with respect to LEO. This paper describes the development of a simple, low cost rf plasma system to produce a well-defined AO and VUV environment. The new system constrained the afterglow flow through two right-angle turns. The afterglow was characterized at three specific locations by (i) optical emission spectroscopy for assessment of electronically excited states, (ii) current measurements, and (iii) UV radiation measurements. KaptonR samples were exposed at the three specific locations in the system and characterized by mass loss for etch rate evaluation, and atomic force microscopy for surface modification. It was found that there is a significant reduction in ionic species, excited species, and UV radiation as the afterglow advances through the right-angle turns. The reduction in charged particle flux is due to recombination within the afterglow as well as neutralization by colliding with the grounded metal chamber walls; similar decrease in UV radiation flux occurs through radiation absorption by the chamber walls. Finally, it is shown that the ground state AO is the dominant reactive specie of the plasma afterglow after passing through the two right-angle turns.
低地球轨道（LEO）航天器外表面的材料会暴露于空间环境的各种成分中，包括原子氧（AO）和太阳紫外线（UV）辐射。利用各种实验设施在地面实验室中模拟LEO对材料的降解和侵蚀，每个设施都有其各自的局限性。射频氧等离子体是一种广泛用于LEO应用材料筛选的模拟设施。然而，复杂的等离子体环境，除了中性氧原子外，还包含激发态物种、电子、离子以及真空紫外线（VUV）辐射，这可能导致对材料与LEO反应性的错误判定。本文描述了一种简单、低成本的射频等离子体系统的开发，以产生明确的AO和VUV环境。新系统通过两个直角转弯来限制余辉流。通过以下方式在三个特定位置对余辉进行了表征：（i）用于评估电子激发态的光发射光谱，（ii）电流测量，以及（iii）UV辐射测量。KaptonR样品在系统的三个特定位置进行暴露，并通过质量损失评估蚀刻速率，以及通过原子力显微镜表征表面改性。结果发现，随着余辉通过直角转弯，离子物种、激发态物种和UV辐射显著减少。带电粒子通量的减少是由于余辉内的复合以及与接地金属腔壁碰撞导致的中和；UV辐射通量的类似减少是通过腔壁的辐射吸收发生的。最后，结果表明，经过两个直角转弯后，基态AO是等离子体余辉的主要反应物种。
