Clive C. Speake

Update on quadruple suspension design for Advanced LIGO

We describe the design of the suspension systems for the major optics for Advanced LIGO, the upgrade to LIGO—the Laser Interferometric Gravitational-Wave Observatory. The design is based on that used in GEO600—the German/UK interferometric gravitational wave detector, with further development to meet the more stringent noise requirements for Advanced LIGO. The test mass suspensions consist of a four-stage or quadruple pendulum for enhanced seismic isolation. To minimize suspension thermal noise, the final stage consists of a silica mirror, 40 kg in mass, suspended from another silica mass by four silica fibres welded to silica ears attached to the sides of the masses using hydroxide-catalysis bonding. The design is chosen to achieve a displacement noise level for each of the seismic and thermal noise contributions of 10^(−19) m/√Hz at 10 Hz, for each test mass. We discuss features of the design which has been developed as a result of experience with prototypes and associated investigations.

Stress-dependent damping in CuBe torsion and flexure suspensions at stresses up to 1.1 GPa

Abstract Stress-dependent damping in Cu Be torsion and flexure suspensions has been measured at stresses up to 1.1 GPa, 95% of the yield stress. The modulus defects of Cu Be increases from 4.3 × 10 −5 to only 6 × 10 −6 in this range. A much larger additional damping, orginating at the clamping interface between the suspension and its support, was identified and eliminated.

Forces and force gradients due to patch fields and contact-potential differences

We derive expressions for the forces and force gradients which exist between infinite parallel metallic surfaces in terms of the spatial distributions of the surface potentials. The main motivation for this is to enable the forces and force gradients to be calculated from electrical measurements of the surface potentials. However, by making some worst-case assumptions about the potential distributions, we establish a limit for the relative displacement of the spacecraft and proof mass in the LISA mission of where is the target acceleration sensitivity, is the proof-mass density, d is the dimension of the proof mass (assumed cubic) and a is the spacing between the proof mass and the surrounding electrodes. The magnitude of the patch-potential variations or contact-potential differences between the plates is parametrized as v.

Sensors and actuators for the Advanced LIGO mirror suspensions

We have developed, produced and characterized integrated sensors, actuators and the related read-out and drive electronics that will be used for the control of the Advanced LIGO suspensions. The overall system consists of the BOSEMs (a displacement sensor with an integrated electromagnetic actuator), the satellite boxes (the BOSEM readout and interface electronics) and six different types of coil-driver units. In this paper, we present the design of this read-out and control system, we discuss the related performance relevant for the Advanced LIGO suspensions, and we report on the experimental activity finalized at the production of the instruments for the Advanced LIGO detectors.

Searching for galactic axions through magnetized media: the QUAX proposal

We present a proposal to search for QCD axions with mass in the 200

Experiment and theory in anelasticity

\mu

An interferometric sensor for satellite drag-free control

eV range, assuming that they make a dominant component of dark matter. Due to the axion-electron spin coupling, their effect is equivalent to the application of an oscillating rf field with frequency and amplitude fixed by the axion mass and coupling respectively. This equivalent magnetic field would produce spin flips in a magnetic sample placed inside a static magnetic field, which determines the resonant interaction at the Larmor frequency. Spin flips would subsequently emit radio frequency photons that can be detected by a suitable quantum counter in an ultra-cryogenic environment. This new detection technique is crucial to keep under control the thermal photon background which would otherwise produce a too large noise.

Novel torsion balance for the measurement of the Newtonian gravitational constant

We briefly review the results of experimental and theoretical studies of anelasticity at low frequencies and we discuss the essential features of models that explain consistently the key aspects of this behaviour. In our original paper on this topic we reported that damping in a compound pendulum at frequencies in the range 10-3-10-2 Hz was consistent with an imaginary component of Youngs modulus for the Cu-Be suspension that was independent of frequency. Damping with this characteristic frequency dependence can also be described in terms of viscous damping whose magnitude varies as the inverse of frequency. With the hindsight provided by our further work we now realize that stick-slip processes can give rise to such losses, not only in the suspensions but also in the structures and clamping mechanism of the suspensions of long-period pendulums.

A 1 kg Mass Comparator Using Flexure-Strip Suspensions: Preliminary Results

We describe a compact interferometer, under development at the University of Birmingham, that could be employed as a zero-stiffness sensor for drag-free satellites. A prototype bench-top polarization-based homodyne interferometer is discussed that achieves a shot-noise limited displacement sensitivity of 3 × 10−12 m Hz1/2 above 60 Hz. We discuss a wavelength modulation technique that will render the interferometer more robust as it enables the absolute difference in interferometric armlengths to be determined.

Preliminary determination of G using the BIPM torsion strip balance

We report on the design and preliminary performance of a novel torsion balance for the measurement of the Newtonian gravitational constant. The design takes advantage of the properties of a wide, heavily loaded torsion strip to enhance the ratio of gravitational signal-to-noise torques beyond that achievable by the traditional Cavendish torsion balance. The results of preliminary experiments suggest that an accuracy of 1 part in 104 should be possible.