The new generation of gravitational waves detectors require unprecedented levels of isolation from seismic noise. This article reviews the seismic isolation strategy and instrumentation developed for ...the Advanced LIGO observatories. It summarizes over a decade of research on active inertial isolation and shows the performance recently achieved at the Advanced LIGO observatories. The paper emphasizes the scientific and technical challenges of this endeavor and how they have been addressed. An overview of the isolation strategy is given. It combines multiple layers of passive and active inertial isolation to provide suitable rejection of seismic noise at all frequencies. A detailed presentation of the three active platforms that have been developed is given. They are the hydraulic pre-isolator, the single-stage internal isolator and the two-stage internal isolator. The architecture, instrumentation, control scheme and isolation results are presented for each of the three systems. Results show that the seismic isolation sub-system meets Advanced LIGO's stringent requirements and robustly supports the operation of the two detectors.
The two-stage vibration isolation and positioning platform provides passive and active isolation in all directions and translation. It uses a unique combination of position sensors, geophones and ...broadband seismometers to provide unprecedented levels of isolation.
•The paper presents the two-stage vibration isolation and positioning platform used in Advanced LIGO gravitational waves detectors.•The system can support a 1000kg of sensitive equipment and operate in ultra-high vacuum.•Each of the two stages provide passive and active isolation in all directions of translation and rotation (12 axis).•The active control strategy uses a unique combination of relative sensors, geophones and broadband seismometers.•The system reduces the motion to the level of 10−11 m/Hz at 1Hz and 10−12 m/Hz at 10Hz.
New generations of gravity wave detectors require unprecedented levels of vibration isolation. This paper presents the final design of the vibration isolation and positioning platform used in Advanced LIGO to support the interferometer's core optics. This five-ton two-and-half-m wide system operating in ultra-high vacuum. It features two stages of isolation mounted in series. The stages are imbricated to reduce the overall height. Each stage provides isolation in all directions of translation and rotation. The system is instrumented with a unique combination of low noise relative and inertial sensors. The active control provides isolation from 0.1Hz to 30Hz. It brings the platform motion down to 10−11 m/Hz at 1Hz. Active and passive isolation combine to bring the platform motion below 10−12 m/Hz at 10Hz. The passive isolation lowers the motion below 10−13 m/Hz at 100Hz. The paper describes how the platform has been engineered not only to meet the isolation requirements, but also to permit the construction, testing, and commissioning process of the fifteen units needed for Advanced LIGO observatories.
The two-stage vibration isolation and positioning platform (BSC-ISI) provides three orders of magnitude of isolation at all frequencies above 1Hz.
•The paper presents near a decade of research on the ...two-stage twelve-axis vibration isolation platforms developed for Advanced LIGO.•This system positions and isolates 1000kg of very sensitive equipment in all directions of translation and rotation.•The system provides more than three orders of magnitude of isolation over a very large bandwidth.•We show how results from the prototyping phases have been used for the production and commissioning of 15 units.•Isolation results show that the system brings the motion below 10−11m/Hz at 1Hz and 10−12 m/Hz at 10Hz.
This paper presents the results of the past seven years of experimental investigation and testing done on the two-stage twelve-axis vibration isolation platform for Advanced LIGO gravity waves observatories. This five-ton two-and-half-meter wide system supports more than a 1000kg of very sensitive equipment. It provides positioning capability and seismic isolation in all directions of translation and rotation. To meet the very stringent requirements of Advanced LIGO, the system must provide more than three orders of magnitude of isolation over a very large bandwidth. It must bring the motion below 10−11 m/Hz at 1Hz and 10−12 m/Hz at 10Hz. A prototype of this system has been built in 2006. It has been extensively tested and analyzed during the following two years. This paper shows how the experimental results obtained with the prototype were used to engineer the final design. It highlights how the engineering solutions implemented not only improved the isolation performance but also greatly simplified the assembly, testing, and commissioning process. During the past two years, five units have been constructed, tested, installed and commissioned at each of the two LIGO observatories. Five other units are being built for an upcoming third observatory. The test results presented show that the system meets the motion requirements, and reach the sensor noise in the control bandwidth.
The Laser Interferometer Gravitational Wave Observatory (LIGO) consists of two widely separated 4 km laser interferometers designed to detect gravitational waves from distant astrophysical sources in ...the frequency range from 10 Hz to 10 kHz. The first observation run of the Advanced LIGO detectors started in September 2015 and ended in January 2016. A strain sensitivity of better than 10 super(-23)/radicalHz was achieved around 100 Hz. Understanding both the fundamental and the technical noise sources was critical for increasing the astrophysical strain sensitivity. The average distance at which coalescing binary black hole systems with individual masses of 30Mmiddot could be detected above a signal-to-noise ratio (SNR) of 8 was 1.3 Gpc, and the range for binary neutron star inspirals was about 75 Mpc. With respect to the initial detectors, the observable volume of the Universe increased by a factor 69 and 43, respectively. These improvements helped Advanced LIGO to detect the gravitational wave signal from the binary black hole coalescence, known as GW150914.
This paper deals with an alternative modal active control approach to reduce sound transmission through a structure excited by an acoustic wave. Active control makes it possible to conserve lightness ...while improving acoustic performances. “Modal mass damping control” is proposed for light and small structures having slight modal overlap. The aim of this control is to modify the modal distribution of high radiation efficiency modes with active modal virtual mass and active modal damping. The active virtual mass effects lower eigen frequencies to less audible frequency range while reducing vibration amplitudes in a broad frequency range. An application of this concept is presented in a simple smart structure. It is harmonically excited on large bandwidth by a normal acoustic plane wave. Results obtained by active modal virtual mass and damping control are compared to other modal control approaches.
Isolating ground-based interferometric gravitational wave observatories from environmental disturbances is one of the great challenges of the advanced detector era. In order to directly observe ...gravitational waves, the detector components and test masses must be highly inertially decoupled from the ground motion not only to sense the faint strain of space-time induced by gravitational waves, but also to maintain the resonance of the very sensitive 4 km interferometers. This article presents the seismic isolation instrumentation and strategy developed for Advanced LIGO interferometers. It reviews over a decade of research on active isolation in the context of gravitational wave detection, and presents the performance recently achieved with the Advanced LIGO observatory. Lastly, it discusses prospects for future developments in active seismic isolation and the anticipated benefits to astrophysical gravitational wave searches. Beyond gravitational wave research, the goal of this article is to provide detailed isolation strategy guidelines for sensitive ground-based physics experiments that may benefit from similar levels of inertial isolation.
SUMMARY
Changes in palaeosecular variation, dipole moment and polarity reversal frequency are salient features of the Earth’s magnetic field over the geological past, yet how these changes are linked ...by the geodynamo remains controversial. To further understand this issue, we provide new absolute (API) and relative (RPI) palaeointensities from the ∼1-km-thick basaltic sequence of Waja (North Ethiopia) emplaced around 31 Ma, yielding an instantaneous virtual dipole moment of 57 ± 9 ZAm2 (1σ, N = 18) and a relative variability in intensity εF = 0.39 ± 0.07 (1σ, N = 19). Our analysis of the API database with strict selection criteria (inclusion of Thellier-style determinations with pTRM checks only, at least five determinations per cooling unit, and within-unit relative standard error lower than 10 per cent) fails to identify any robust correlation between changes in dipole moment and reversal frequency over the past 155 Myr. More convincingly, the available RPI results are consistent with an increase of the palaeosecular-variation proxy εF with reversal rate, as predicted by numerical dynamo simulations. We also find that the API-based estimate εF = 0.40 ± 0.03 (1σ, N = 104), computed from the filtered version of the World Palaeointensity Database for the 0.77–31 Ma interval, is consistent with the scaling rule, suggesting that the API record has been sufficiently sampled over the past 31 Ma. We thus speculate that the absence of negative correlation between changes in dipole moment and reversal frequency in the API database over the past 155 Myr may be the result of insufficient sampling prior to 31 Ma rather than the signature of an intrinsic geomagnetic feature.
Goal-directed approaches to perception usually consider that distance perception is shaped by the body and its potential for interaction. Although this phenomenon has been extensively investigated in ...the field of perception, little is known about the effect of motor interactions on memory, and how they shape the global representation of large-scale spaces. To investigate this question, we designed an immersive virtual reality environment in which participants had to learn the positions of several items. Half of the participants had to physically (but virtually) grab the items with their hand and drop them at specified locations (active condition). The other half of the participants were simply shown the items which appeared at the specified position without interacting with them (passive condition). Half of the items used during learning were images of manipulable objects, and the other half were non manipulable objects. Participants were subsequently asked to draw a map of the virtual environment from memory, and to position all the items in it. Results show that active participants recalled the global shape of the spatial layout less precisely, and made more absolute distance errors than passive participants. Moreover, global scaling compression bias was higher for active participants than for passive participants. Interestingly, manipulable items showed a greater compression bias compared to non-manipulable items, yet they had no effect on correlation scores and absolute non-directional distance errors. These results are discussed according to grounded approaches of spatial cognition, emphasizing motor simulation as a possible mechanism for position retrieval from memory.
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