Technology Demonstration for Mid-Frequency Gravitational-Wave Detector

该奖项支持建造和演示传感器，这些传感器将能够测量当地引力场中的极微小变化。其主要动机是建造一种新型的引力波探测器，它将能够探测到迄今为止很少被探索的频率范围内的引力波信号，低于NSF的LIGO(和所有其他地面探测器)可以探测到的频率，但高于未来的天基探测器LISA将覆盖的范围，从而为进一步利用引力波探索物理学和天体物理学提供了一个新的窗口。在这种中等范围内检测信号极具挑战性，需要极低噪音的传感器和几乎不受震动影响的读出电子设备。超导材料和量子干涉装置放大器应该能够应对这些挑战，如果使用一种配置来比较多个“测试质量”，这些测试质量的微小运动直接使用过冷电路进行比较。本项目是建造一个带有两个测试质量的组件，并确认其在目标频率范围内具有预期的稳定性和灵敏度。作为一个额外的好处，预计这种传感器技术还可以被改装成快速感知地下深处移动的断层带来的细微重力变化，从而在地震波到达地表之前更快地发出地震预警，从而潜在地拯救生命并减少对基础设施的破坏。该项目的传感器设计基于马里兰引力实验小组在液氦温度(4K)下悬浮超导试块和使用低温电路感应差动位移的经验。对相对于普通刚架的位移的直接差分传感测量重力梯度。测试质量的四面体排列足以感知局部引力场变化的所有张量分量；这种设计被称为Mini-SOGRO。该项目将建造一个具有两个测试质量的组件，使用的设计预计将在频率低于0.1赫兹的差动检测模式下实现Q因数大于10^6，使用超导电容桥、SQUID放大器和锁定放大器读出的电容检测。新设计的一个关键特征是在测试质量表面上使用多个弯曲的脊线，与线圈策略性地对齐，以产生“负弹簧”，从而缓解测试质量上悬浮(和传感)场的内在非线性，从而实现极低的谐振频率。Q将被测量并评估共模拒绝，即对外壳振动的稳健性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports the construction and demonstration of sensors that will be able to measure extremely small variations in the local gravitational field. The main motivation is to make it possible to build a new type of gravitational wave detector that will be able to detect gravitational-wave signals in a so-far little-explored frequency range, lower than what NSF's LIGO (and all other ground-based detectors) can sense, but higher than what the future space-based detector LISA will cover, thus enabling a new window to further explore physics and astrophysics with gravitational waves. Detecting signals in that middle range is supremely challenging, requiring extremely low-noise sensors and readout electronics that are virtually immune from vibrations. Superconducting materials and quantum-interference-device amplifiers should be able to meet those challenges if used in a configuration that compares multiple "test masses" whose tiny motions are compared directly using super-cooled circuits. This project is to construct an assembly with two test masses and confirm that it has the expected stability and sensitivity in the target frequency range. As an added benefit, it is anticipated that this sensor technique could also be adapted to rapidly sense the subtle gravitational changes from shifting faults deep underground, enabling faster early warning of earthquakes before the seismic waves reach the surface and thereby potentially saving lives and reducing damage to infrastructure.The sensor design for this project builds on the Maryland Gravitation Experiment group's experience with levitating superconducting test masses and sensing differential displacements using cryogenic circuits at liquid helium temperature (4 K). Direct differential sensing of displacements relative to a common rigid frame measures gravity gradients. A tetrahedral arrangement of test masses is sufficient to sense all tensor components of variations of the local gravitational field; this design is called Mini-SOGRO. This project will construct an assembly with two test masses, using a design that is expected to achieve Q factors greater than 10^6 in the differential sensing mode at frequencies below 0.1 Hz using capacitive sensing with superconducting capacitance bridges, SQUID amplifiers and lock-in amplifier readout. A key feature of the new design is the use of multiple curved ridges on the test mass surface, strategically aligned with coils, to produce a "negative spring" that will mitigate the intrinsic nonlinearity of the levitation (and sensing) fields on the test masses and thereby make it possible to achieve very low resonant frequency. The Q will be measured and the common-mode rejection, i.e. robustness to vibrations of the housing, assessed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.