扭秤周期法测G实验中的石英丝特性研究

The anelasticity is one of the largest systematic errors in determining G with the time-of-swing method. As proposed by Kuroda, the anelasticity is mainly limited by the fiber's Q factor. As a new kind of fiber with small mechanical loss, the Q factor of the silica fiber is generally higher than 100000, which is helpful to reduce the anelasticity. We will prepare silica fibers with diameters of 45-55 micrometers and length of 900 millimeters. To reduce the potential electrostatic effect, the silica fibers will be coated with thin layers of germanium and bismuth by using a magnetron sputtering coater. The properties of silica fibers, such as the thermoelasticity, nonlinearity, stability of the period, and so on, will be researched systematically. In our new G measurement with the time-of-swing method, we will use the coated silica fiber with Q factor of more than 100000 instead of the tungsten fiber to measure G directly, and the anelasticity will be controlled within 3ppm. Besides, the related researches on silica fiber will be used in other experiments with high precision, such as the tests of weak equivalence principle and gravitational inverse square law.

扭丝滞弹性效应是扭秤周期法测G实验中最大的系统误差之一。国际上关于该问题的理论和实验研究结果表明Q值约1000的传统金属丝滞弹性效应高达300ppm。作为一种新型低耗散扭丝，高纯度石英丝的Q值普遍在100000以上，即石英丝能够有效地减小滞弹性效应给扭秤实验带来的系统误差。本课题拟研制直径45-55微米、长度约900毫米的高Q值石英丝。通过镀膜技术解决丝不导电带来的静电干扰问题，镀膜后实现丝两端电阻小于1兆欧姆、Q值大于100000的目标。同时我们将系统地研究高Q值石英丝的性质，如热弹性、非线性、周期稳定性等。在对石英丝特性研究的基础上，我们将采用镀膜石英丝进行扭秤周期法测G实验，实现将滞弹性效应控制在3ppm以内的目标。关于高Q值镀膜石英丝特性的研究，亦将为弱等效原理和牛顿反平方定律的实验检验等其它高精度扭秤实验提供经验。

作为一种新型低耗散扭丝，高纯度石英丝的Q值普遍在100000以上。在精密引力测量实验中，采用高Q值石英丝能够有效地减小滞弹性效应、提高扭秤周期的测量精度和降低系统的热噪声。本项目制备了高 Q 值的石英丝，裸石英丝Q值高于500000，镀膜后石英丝的Q值达到100000水平，丝两端电阻约为4兆欧姆；测量了石英丝直径的均匀性、抗拉强度等参量；完成了镀膜石英丝悬挂的扭秤系统静电作用调制实验；测量了石英丝的热弹性、非线性效应，给出响应系数；完成石英丝扭秤系统的周期稳定性测量，三天扭秤数据的周期测量精度达到20us。将石英丝扭秤系统应用到万有引力常数G的精确测量实验中，测量的重复性达到15ppm，为目前国际上同种方法的最好水平。本项目基于高Q值石英丝的理论和实验研究将应用在其它精密测量与基础应用领域，如更高精度的检验等效原理、牛顿反平方定律等。