RUI: Exploring Charging Issues in Third-Generation Gravitational-Wave Interferometers

RUI：探索第三代引力波干涉仪的充电问题

• 批准号: 1404269
• 负责人: Dennis Ugolini
• 金额: $ 14.32万
• 依托单位: Trinity University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1404269&HistoricalAwards=false
• 关键词: RUI; Exploring; Charging; Issues; Third

Einstein's Theory of General Relativity predicts that the motion of massive astronomical bodies such as black holes or supernovae will generate tiny changes in the curvature of space called gravitational waves. Experiments such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) are designed to detect these waves by measuring the length difference between two paths with laser light. The optics in these experiments are suspended in vacuum to isolate them from all forms of vibration. With no air to conduct it away, excess surface charge can build up on the optics over time. The motion of this charge changes the surrounding electric field, vibrating the optic and degrading the sensitivity of the experiment. The group at Trinity University has been measuring the rate at which surface charge builds up and a method of removing the charge that does not harm the delicate reflective coatings on the optics. Funding from this grant supports the completion of a charge removal system for delivery to the LIGO observatories and the study of the effect of different optical cleaning and handling techniques on the mobility of surface charge, and even the individual charge motions themselves. Pursuing this research will help improve the sensitivity of Advanced LIGO and future gravitational-wave detectors, for which surface charge has been a known limiting noise source since 2006. The funding supports undergraduate research at Trinity University, where students can gain valuable experience working locally on a scaled-down vacuum system prototype while contributing to the overall LIGO research effort. The Laser Interferometer Gravitational-Wave Observatory (LIGO) is most sensitive to gravitational waves at signal frequencies near 100 Hz. A limiting noise source at these frequencies is surface charge on test masses, the motion of which generates fluctuating electric fields that vibrate the masses. The noise contribution depends on the charge magnitude and the correlation time for charge motion. This project tackles three issues related to charging noise. One is to finalize a deliverable discharging system and assist with its installation at the LIGO observatories. Prototype systems using ionized nitrogen gas have been demonstrated at both MIT and Trinity University, but it still must be verified that the process does not damage the test mass reflective coating. This is done by acquiring a test mass of known absorption, exposing it to an ionized nitrogen system, and then having its absorption retested (this process has been used in cooperation with Stanford University for previous discharging techniques). The second is to characterize the relaxation time constant and charging/discharging rate for Advanced LIGO test masses using different cleaning and handling techniques, to determine which methods will reduce charging noise. This requires obtaining several LIGO test mass witness samples, applying different cleaning techniques (methanol, liquinox, First Contact, etc.) to each, moving them into a vacuum system, charging with a high-voltage electrode pattern, and then using a Kelvin probe to measure the rate at which the deposited charge dissipates across the face of the test mass. This methodology will also be applied to proposed optical coatings and substrates for third-generation interferometers in cooperation with the Optics Working Group of the LIGO Scientific Collaboration. The third is to modify an existing atomic force microscope at Trinity University so that it can perform Kelvin probe microscopy. This will make it possible tovisualize individual charge "hopping" across an insulating surface, with the goal of refining the Markov process model of low frequency noise contributions.

爱因斯坦的广义相对论预言，黑洞或超新星等大质量天体的运动将产生空间曲率的微小变化，称为引力波。 激光干涉引力波天文台（LIGO）等实验旨在通过测量激光两条路径之间的长度差来检测这些波。 这些实验中的光学元件被悬挂在真空中，以使它们与所有形式的振动隔离。 由于没有空气将其传导走，随着时间的推移，多余的表面电荷会在光学器件上积聚。 这种电荷的运动改变了周围的电场，振动了光学元件，降低了实验的灵敏度。 Trinity大学的研究小组一直在测量表面电荷积聚的速度，以及一种不损害光学器件上精致的反射涂层的去除电荷的方法。 这笔赠款的资金支持完成一个电荷去除系统，以交付给LIGO天文台，并研究不同的光学清洁和处理技术对表面电荷流动性的影响，甚至是单个电荷运动本身。 进行这项研究将有助于提高高级LIGO和未来引力波探测器的灵敏度，自2006年以来，表面电荷一直是已知的限制噪声源。 这笔资金支持Trinity大学的本科生研究，在那里学生可以获得宝贵的经验，在当地工作的规模缩小的真空系统原型，同时有助于整个LIGO的研究工作。激光干涉引力波天文台（LIGO）对信号频率接近100 Hz的引力波最为敏感。 在这些频率下的限制噪声源是测试质量上的表面电荷，其运动产生使质量振动的波动电场。 噪声的贡献取决于电荷的大小和电荷运动的相关时间。 该项目解决了与充电噪声相关的三个问题。 一个是最终确定一个可交付的放电系统，并协助其在LIGO天文台的安装。 使用电离氮气的原型系统已经在MIT和Trinity大学进行了演示，但仍然必须验证该过程不会损坏测试质量反射涂层。 这是通过获取已知吸收的测试质量，将其暴露于电离氮系统，然后重新测试其吸收来完成的（该过程已与斯坦福大学合作用于先前的放电技术）。 第二个是使用不同的清洁和处理技术来表征Advanced LIGO测试质量的弛豫时间常数和充电/放电速率，以确定哪些方法可以降低充电噪声。 这需要获得几个LIGO测试质量见证样本，应用不同的清洁技术（甲醇，Liquinox，First Contact等）。将它们移动到真空系统中，用高压电极图案充电，然后使用开尔文探针测量沉积的电荷在测试块表面上消散的速率。 这种方法也将应用于与LIGO科学合作组织光学工作组合作的第三代干涉仪的光学涂层和基底。 第三个是修改Trinity大学现有的原子力显微镜，使其能够进行开尔文探针显微镜。 这将使人们有可能看到单个电荷在绝缘表面上的“跳跃”，目的是改进低频噪声贡献的马尔可夫过程模型。