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Characterization of neutral gas densities in the plume and the discharge chamber of an ion thruster using two-photon absorption laser induced fluorescence spectroscopy

使用双光子吸收激光诱导荧光光谱表征离子推进器的羽流和放电室中的中性气体密度

基本信息

批准号：
252723394
负责人：
Dr.-Ing. Christoph Eichhorn
金额：
--
依托单位：
Leibniz-Institut für Oberflächenmodifizierung e.V. (IOM)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/252723394?language=en
关键词：
Characterization neutral gas densities plume

项目摘要

Two-photon absorption laser induced fluorescence spectroscopy represents an excellent method to accurately determine atomic and molecular ground state densities in low temperature plasma. For several species such as H, N, O, Kr, or Xe, the simultaneous absorption of two laser photons allows excitation from the ground state, while circumventing laser wavelengths in the VUV. However, compared to various published plasmadiagnostic studies on atomic H, N and O species, this method has been applied rather seldom for investigations of atom number densities in rare gas plasma discharges such as in Kr or Xe.With respect to the operation of ion sources, rare gases are commonly used to conduct processes related to ion beam sputter deposition or surface modifications within terrestrial applications, and, furthermore, as propellants of electric spacecraft propulsion devices, in particular of both gridded ion- and Hall-effect thrusters. Here, the experimental characterization of the plume, as well as of the discharge region, is indispensable to achieve a better understanding of important physical phenomena such as the emergence of a charge exchange plasma component near the thruster exit. In addition, results of these investigations are needed to optimize electric propulsion devices.In the thruster plasma, neutral gas species mainly occur due to incomplete ionization of the propellant in the discharge chamber, as part of the neutralizer flow and as background atoms in ground test facilities. In particular, charge exchange collisions between fast ions and slow thermal neutral gas atoms may cause a backflow of ionized atoms of the ion beam, which can result in critical issues such as electric charging or erosion of spacecraft or thruster components by ion impingement. Therefore, plasmadiagnostic investigations aiming at the quantitative analysis of number densities of neutral atoms are of particular interest, since neutral gas species can not be detected with standard ion beam diagnostic tools such as Faraday cups or ExB, RPA and Langmuir probes.Within the proposed project, measurements using the two-photon absorption laser induced fluorescence technique will be carried out to determine local ground state densities of neutral xenon in the plume of an ion thruster. From the measured number density distributions, neutral particle fractions emerged from charge exchange processes shall be estimated. In addition, the fraction of fast neutrals shall be measured directly at the Doppler-shifted absorption wavelength for appropriate thruster operating conditions. Moreover, experimental investigations in the discharge will be conducted mounting appropriate optical access to the chamber housing, allowing for the examination of neutral gas density distributions that are critical to the validation of numerical discharge models. Additional to the experiments in xenon, ion source resp. thruster operating with krypton as propellant will be investigated.

双光子吸收激光诱导荧光光谱是一种精确测定低温等离子体中原子和分子基态密度的优良方法。对于H， N， O， Kr或Xe等几种物质，同时吸收两个激光光子允许从基态激发，同时绕过VUV中的激光波长。然而，与各种已发表的关于H、N和O原子的等离子体诊断研究相比，这种方法很少用于研究稀有气体等离子体放电（如Kr或Xe）中的原子序数密度。关于离子源的操作，稀有气体通常用于在地面应用中进行与离子束溅射沉积或表面修饰有关的过程，此外，还用作电动航天器推进装置的推进剂，特别是栅格离子和霍尔效应推进器。在这里，羽流的实验表征以及放电区域的实验表征对于更好地理解重要的物理现象是必不可少的，例如在推进器出口附近出现电荷交换等离子体成分。此外，需要这些研究结果来优化电力推进装置。在推力器等离子体中，中性气体主要是由于推进剂在放电室内的不完全电离而产生的，作为中和剂流动的一部分，在地面试验设施中作为背景原子。特别是，快离子与慢热中性气体原子之间的电荷交换碰撞可能导致离子束的电离原子回流，这可能导致诸如电荷或离子撞击对航天器或推进器部件的侵蚀等关键问题。因此，针对中性原子数量密度的定量分析的等离子体诊断研究特别有趣，因为中性气体无法用标准离子束诊断工具（如法拉第杯或ExB， RPA和Langmuir探针）检测到。在提议的项目中，将使用双光子吸收激光诱导荧光技术进行测量，以确定离子推进器羽流中中性氙的局部基态密度。从测量的数密度分布中，可以估计出电荷交换过程中产生的中性粒子分数。此外，在适当的推进器工作条件下，应直接在多普勒位移吸收波长处测量快中性的比例。此外，将对放电进行实验研究，安装适当的光学通道到腔室外壳，允许检查中性气体密度分布，这对数值放电模型的验证至关重要。除氙、离子源实验外。将研究以氪作为推进剂的推进器。