Abstract
The high mechanical losses of the multilayer reflecting coating deposited on the mirror surface account for the main contribution to the thermal noise, limiting the sensitivity in the ...mid-frequency region of the detection band of the future gravitational waves detectors. Several European laboratories of the Virgo Collaboration have joined their efforts to improve the coating mechanical performances. The research lines of this collaboration are all focused on amorphous coatings, which represent a viable solution for the future GW detector generations. The main target is to find a way to reduce by a factor three the mechanical losses of the coating for the next generation of room temperature operating detectors. Some activities are also meant to be relevant for cryogenic operations. The status of this collaborative work will be described as well as the latest results of the different research lines.
The multi-band template analysis (MBTA) pipeline is a low-latency coincident analysis pipeline for the detection of gravitational waves (GWs) from compact binary coalescences. MBTA runs with a low ...computational cost, and can identify candidate GW events online with a sub-minute latency. The low computational running cost of MBTA also makes it useful for data quality studies. Events detected by MBTA online can be used to alert astronomical partners for electromagnetic follow-up. We outline the current status of MBTA and give details of recent pipeline upgrades and validation tests that were performed in preparation for the first advanced detector observing period. The MBTA pipeline is ready for the outset of the advanced detector era and the exciting prospects it will bring.
The Advanced Virgo monolithic fused silica suspension Aisa, D.; Aisa, S.; Campeggi, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2016, Volume:
824
Journal Article
Peer reviewed
The detection of gravitational waves is one of the most challenging prospects faced by experimental physicists. Suspension thermal noise is an important noise source at operating frequencies between ...approximately 10 and 30Hz, and represents a limit to the sensitivity of the ground based interferometric gravitational wave detectors. Its effects can be reduced by minimizing the losses and by optimizing the geometry of the suspension fiber as well as its attachment system. In this proceeding we will describe the mirrors double stage monolithic suspension system to be used in the Advanced Virgo (AdV) detector. We also present the results of the thermal noise study, performed with the help of a finite elements model, taking into account the precise geometry of the fibers attachment systems on the suspension elements. We shall demonstrate the suitability of this suspension for installation in AdV.
•Suspension system design for the test masses of the gravitational wave detectors.•Finite element model studies.•Suspension thermal noise studies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The thermal noise coupling with the displacement of the mirrors of a gravitational wave interferometric detector is a limit to its sensitivity in a range of frequencies from about 10
Hz to few ...hundreds of Hz; fused silica proved to be a very suitable material to reduce this source of noise for the first generation of detectors. The future advanced detectors are planning to make use of fused silica mirrors and suspending elements in a monolithic arrangement: in these conditions, the main contribution to the thermal noise will come from the amorphous multilayered coating deposited on the mirrors. This paper is focused on the multiple advantages provided by the use of fused silica material in a present day interferometric detector; a new suspension for measurements of the acoustic attenuation in fused silica is presented together with the loss angle dependance on frequency and aspect ratio. Furthermore we report on the status of the art of the research activity on fused silica wires production and characterization and coating thermal noise accomplished by the Firenze–Urbino Virgo group.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In order to reduce the suspension thermal noise, the second generation GW interferometric detectors will employ monolithic suspensions in fused silica to hold the mirrors. The fibres are produced by ...melting and pulling apart a fused silica rod, obtaining a long thin wire with two thicker heads. The dynamics of such a fibre is in principle different from that of a cylindrical, regular fibre, because most of the deformation energy is stored in the neck region where the diameter is variable. This is an advantage, since adjusting the neck tapering, a thermoelastic noise cancellation effect can be obtained. Therefore, a careful study of the suspensions behavior is necessary to estimate the overall noise and to optimize the control strategy. To simplify the control design, a simple three segment model for the silica fibres has been developed, fully equivalent to the beam equation at low frequencies. The model, analytically proved for a regular cylindrical fibre, can be extended to a fibre with tapered necks, provided that the equivalent bending length is suitably measured. We developed a tool to measure the position of the bending point for each fibre, thus allowing to experimentally check the validity of the model. A numerical code has been written to solve the beam equation for wires with varying diameter. This code confirms the validity of the three segment model. Moreover, it is possible to extend the solution to higher frequencies thus computing the transfer function and the energy distribution of the suspension system and estimating the thermal noise contribution.
Thermal noise of the mirrors limits the sensitivity of interferometric gravitational-wave detectors in the frequency range between 50 and 300 Hz. According to the fluctuation--dissipation theorem, ...the thermal noise amplitude is proportional to the mechanical loss of the mirrors. Fused silica substrates loss angle widely ranges from 10-9 to 10-6, while for the coating it is around 10-4. Loss angle measurements in ultra low mechanical loss materials are normally affected by a large systematic error due to the excess losses introduced by the suspension system used to hold the samples. An innovative measurement system Gentle Nodal Suspension, where the disk-shaped sample is suspended in equilibrium on the top of a sphere, touching one of the nodal points of vibration, has been developed in INFN Florence Virgo laboratory. The advantages of this system are as follows: (i) the good reproducibility of loss angle measurements; (ii) one surface only (in any case uncoated) of the sample is touched; (iii) the contact surface is minimized because of the absence of applied forces. This suspension has been used to characterize annealing and coating deposition effects on the mechanical quality factor Q. An interesting comparison/analysis of these effects on mechanical, optical, chemical and surface properties using spectroscopic ellipsometry, x-ray photoelectron spectroscopy and atomic force microscopy has been carried out.
Status of the Virgo project Accadia, T; Acernese, F; Antonucci, F ...
Classical and quantum gravity,
06/2011, Volume:
28, Issue:
11
Journal Article, Conference Proceeding
Peer reviewed
Open access
We describe the present state and future evolution of the Virgo gravitational wave detector, realized by the Virgo Collaboration at the European Gravitational Observatory, in Cascina near Pisa in ...Italy. We summarize basic principles of the operation and the design features of the Virgo detector. We present the sensitivity evolution due to a series of intermediate upgrades called Virgo+ which is being completed this year and includes new monolithic suspensions. We describe the present scientific potential of the detector. Finally we discuss the plans for the second generation of the detector, called Advanced Virgo, introducing its new features, the expected sensitivity evolution and the scientific potential.
Mechanical spectroscopy gives information on the structure of solids and their relaxation mechanisms through the measurements of the elastic constants and the mechanical loss angle of materials. One ...common way to estimate these quantities is the resonant method where the frequency and the characteristic decay time of oscillations are measured. Since many solid materials can be easily found in the shape of thin disc we have investigated the mechanical loss of these resonators and we have found experimentally that the loss angle dependence on the mode is not trivial but rather follow a distribution of modes into families. We give a model that is able to justify the existence of these families and to predict the level of losses in silicon, silica and brass discs. The model considers the thermoelastic effect and the excess damping caused by the condition of the disc edge. The results of this research are relevant to the research on thin films that are deposited on thin discs like the optical coatings used on the mirrors for the gravitational wave detectors.
•It provides the first experimental evidence and justification of mode families in loss measurements in discs.•A simple and reliable model of thermoelastic loss in thin discs is provided.•A method of calculation of thermoelastic loss in thick cylinder and non-isotropic materials is provided.•Total loss expression is provided in the most general case of heterogeneous systems with multiple loss mechanisms.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A direct approach to reduce the thermal noise contribution to the sensitivity limit of a GW interferometric detector is the cryogenic cooling of the mirrors and mirrors suspensions. Future ...generations of detectors are foreseen to implement this solution. Silicon has been proposed as a candidate material, thanks to its very low intrinsic loss angle at low temperatures and due to its very high thermal conductivity, allowing the heat deposited in the mirrors by high power lasers to be efficiently extracted. To accomplish such a scheme, both mirror masses and suspension elements must be made of silicon, then bonded together forming a quasi-monolithic stage. Elements can be assembled using hydroxide-catalysis silicate bonding, as for silica monolithic joints. The effect of Si to Si bonding on suspension thermal conductance has therefore to be experimentally studied. A measurement of the effect of silicate bonding on thermal conductance carried out on 1 inch thick silicon bonded samples, from room temperature down to 77 K, is reported. In the explored temperature range, the silicate bonding does not seem to affect in a relevant way the sample conductance.
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