Hareem Tariq

The linear variable differential transformer (LVDT) position sensor for gravitational wave interferometer low-frequency controls

Low-power, ultra-high-vacuum compatible, non-contacting position sensors with nanometer resolution and centimeter dynamic range have been developed, built and tested. They have been designed at Virgo as the sensors for low-frequency modal damping of Seismic Attenuation System chains in Gravitational Wave interferometers and sub-micron absolute mirror positioning. One type of these linear variable differential transformers (LVDTs) has been designed to be also insensitive to transversal displacement thus allowing 3D movement of the sensor head while still precisely reading its position along the sensitivity axis. A second LVDT geometry has been designed to measure the displacement of the vertical seismic attenuation filters from their nominal position. Unlike the commercial LVDTs, mostly based on magnetic cores, the LVDTs described here exert no force on the measured structure.

Mirror suspension system for the TAMA SAS

Several R&D programmes are ongoing to develop the next generation of interferometric gravitational wave detectors providing the superior sensitivity desired for refined astronomical observations. In order to obtain a wide observation band at low frequencies, the optics need to be isolated from the seismic noise. The TAMA SAS (seismic attenuation system) has been developed within an international collaboration between TAMA, LIGO, and some European institutes, with the main objective of achieving sufficient low-frequency seismic attenuation (−180 dB at 10 HZ). The system suppresses seismic noise well below the other noise levels starting at very low frequencies above 10 Hz. It also includes an active inertial damping system to decrease the residual motion of the optics enough to allow a stable operation of the interferometer. The TAMA SAS also comprises a sophisticated mirror suspension subsystem (SUS). The SUS provides support for the optics and vibration isolation complementing the SAS performance. The SUS is equipped with a totally passive magnetic damper to suppress internal resonances without degrading the thermal noise performance. In this paper we discuss the SUS details and present prototype results.

Seismic attenuation performance of the first prototype of a geometric anti-spring filter

Abstract Next generation gravitational wave detectors, such as an advanced LIGO, will generally require improved sensitivity at low frequency. One of the principal challenges for low-frequency sensitivity is isolation from seismic motion. A mechanical seismic isolation filter specifically studied for the next generation of the LIGO detectors, based on a geometric anti-spring concept, has been developed with the aim to provide thermal noise limited sensitivity to frequencies of 10 Hz . The design and the performance of the isolation filter, mainly for the vertical degree of freedom are discussed.

Constant force actuator for gravitational wave detector's seismic attenuation systems (SAS)

We have designed, tested and implemented a UHV-compatible, low-noise, non-contacting force actuator for DC positioning and inertial damping of the rigid body resonances of the Seismic Attenuation System (SAS) designed for the TAMA Gravitational Wave Interferometer. The actuator fully satisfies the stringent zero-force-gradient requirements that are necessary to prevent re-injecting seismic noise into the SAS chain. The actuators closed magnetic field design makes for particularly low power requirements, and low susceptibility to external perturbations. The actuator retains enough strength to absorb seismic perturbations even during small earthquakes.

Anatomy of the TAMA SAS seismic attenuation system

The TAMA SAS seismic attenuation system was developed to provide the extremely high level of seismic isolation required by the next generation of interferometric gravitational wave detectors to achieve the desired sensitivity at low frequencies. Our aim was to provide good performance at frequencies above ~10 Hz, while utilizing only passive subsystems in the sensitive frequency band of the TAMA interferometric gravitational wave detectors. The only active feedback is relegated below 6 Hz and it is used to damp the rigid body resonances of the attenuation chain. Simulations, based on subsystem performance characterizations, indicate that the system can achieve rms mirror residual motion measured in a few tens of nanometres. We will give a brief overview of the subsystems and point out some of the characterization results, supporting our claims of achieved performance. SAS is a passive, UHV compatible and low cost system. It is likely that extremely sensitive experiments in other fields will also profit from our study.