Low-frequency internal friction in clamped-free thin wires

We present a series of internal friction measurements for the normal modes of circular fibres made of different materials, that can suspend the test masses of an interferometric gravity wave detector. For metallic wires, the frequency independent loss angle ranges between 10 y3 and 10 y4 . The losses in fused silica are two orders of magnitude lower than those in metals

One-side heating test and modeling of tubular receivers equipped with turbulence promoters for solar tower applications

Tubular receivers in central tower systems suffer the high mechanical stresses caused by the temperature gradient typically established along the tube and across its circumference due to the one-side heating. In the present work, the thermal behavior of three different absorber tubes is investigated both experimentally and numerically. The tubes, manufactured in Cr alloy 718 (Inconel®), were smooth or with repeated rib-roughness (annular or helical ribs), and were tested at the solar furnace SF60 of the Plataforma Solar de Almería (PSA) in 2017 within the international access program of SFERA II project, financed by the EU. The specific focus of the tests was the assessment of the role of turbulence promoters in reducing the peak wall temperature when a strong one-side heating is present, contributing to the reduction of the thermal gradients between the irradiated and the non-irradiated (back) side of the tube. The experimental results show that the use of turbulence promoters reduce the wall temperature with respect to the case of a smooth tube, as expected, although the comparison between the samples is not trivial in view of the change in the optical properties induced by the progressive oxidation of the irradiated surface. Computational Fluid Dynamic (CFD) 3D models have been developed for the three samples and they have proven the capability to very-well reproduce the experimental results. A fair comparison between the different simulated tubes in the same controlled conditions of one-side heating has been performed numerically, assessing quantitatively the temperature reduction induced by the turbulence promoters, and the best performance of the Inconel® tube equipped with helices

Mechanical quality factor of a sapphire fiber at cryogenic temperatures

A mechanical quality factor of $1.1 \times 10^{7}$ was obtained for the 199 Hz bending vibrational mode in a monocrystalline sapphire fiber at 6 K. Consequently, we confirm that pendulum thermal noise of cryogenic mirrors used for gravitational wave detectors can be reduced by the sapphire fiber suspension.Comment: To be published to Physiscs Letters A. Number of pages: 10 Number of figures: 5 Number of tables:

MECHANICAL SHOT NOISE INDUCED BY CREEP IN SUSPENSION DEVICES

Abstract The sensitivity curve of a gravitational wave interferometric detector like VIRGO might be seriously limited by the mechanical shot noise induced by stationary creep in the heavily loaded mechanical suspension components (wires, spring blades, etc.). We quantify this effect and discuss possible improvements which could be implemented without major design alterations

Pendulum Mode Thermal Noise in Advanced Interferometers: A comparison of Fused Silica Fibers and Ribbons in the Presence of Surface Loss

The use of fused-silica ribbons as suspensions in gravitational wave interferometers can result in significant improvements in pendulum mode thermal noise. Surface loss sets a lower bound to the level of noise achievable, at what level depends on the dissipation depth and other physical parameters. For LIGO II, the high breaking strength of pristine fused silica filaments, the correct choice of ribbon aspect ratio (to minimize thermoelastic damping), and low dissipation depth combined with the other achievable parameters can reduce the pendulum mode thermal noise in a ribbon suspension well below the radiation pressure noise. Despite producing higher levels of pendulum mode thermal noise, cylindrical fiber suspensions provide an acceptable alternative for LIGO II, should unforeseen problems with ribbon suspensions arise.Comment: Submitted to Physics Letters A (Dec. 14, 1999). Resubmitted to Physics Letters A (Apr. 3, 2000) after internal (LSC) review process. PACS - 04.80.Nn, 95.55.Ym, 05.40.C

Noise parametric identification and whitening for LIGO 40-meter interferometer data

We report the analysis we made on data taken by Caltech 40-meter prototype interferometer to identify the noise power spectral density and to whiten the sequence of noise. We concentrate our study on data taken in November 1994, in particular we analyzed two frames of data: the 18nov94.2.frame and the 19nov94.2.frame. We show that it is possible to whiten these data, to a good degree of whiteness, using a high order whitening filter. Moreover we can choose to whiten only restricted band of frequencies around the region we are interested in, obtaining a higher level of whiteness.Comment: 11 pages, 15 figures, accepted for publication by Physical Review

Apparatus for dimensional characterization of fused silica fibers for the suspensions of advanced gravitational wave detectors

Detection of gravitational waves from astrophysical sources remains one of the most challenging problems faced by experimental physicists. A significant limit to the sensitivity of future long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test mass mirrors and their suspensions. Suspension thermal noise results from mechanical dissipation in the fused silica suspension fibers suspending the test mass mirrors and is therefore an important noise source at operating frequencies between ∼10 and 30 Hz. This dissipation occurs due to a combination of thermoelastic damping, surface and bulk losses. Its effects can be reduced by optimizing the thermoelastic and surface loss, and these parameters are a function of the cross sectional dimensions of the fiber along its length. This paper presents a new apparatus capable of high resolution measurements of the cross sectional dimensions of suspension fibers of both rectangular and circular cross section, suitable for use in advanced detector mirror suspensions

Thermoelastic dissipation in inhomogeneous media: loss measurements and displacement noise in coated test masses for interferometric gravitational wave detectors

The displacement noise in the test mass mirrors of interferometric gravitational wave detectors is proportional to their elastic dissipation at the observation frequencies. In this paper, we analyze one fundamental source of dissipation in thin coatings, thermoelastic damping associated with the dissimilar thermal and elastic properties of the film and the substrate. We obtain expressions for the thermoelastic dissipation factor necessary to interpret resonant loss measurements, and for the spectral density of displacement noise imposed on a Gaussian beam reflected from the face of a coated mass. The predicted size of these effects is large enough to affect the interpretation of loss measurements, and to influence design choices in advanced gravitational wave detectors.Comment: 42 pages, 7 figures, uses REVTeX