Gravitational Radiation Antenna Research Articles

Development of a 1.5-tonne niobium gravitational radiational antenna

A 1.5-tonne Nb gravitational radiation antenna is described. Problems associated with a noncontacting magnetically levitated parametric upconverter transducer are discussed, and a system using a bonded microwave reentrant cavity and bonded mechanical impedance transformer is described and analyzed in detail. It is shown that such an antenna can be expected to achieve a noise temperature of ∼1 mK. An ultralow phase noise tunable microwave source for the transducer pump signal is described, as well as precision bonding techniques which yield a mechanical positioning accuracy of 10−6 m, and a reproducibility of 10−8 m.

Parametric Transducer for Gravitational Radiation Detector

A low-noise parametric vibration transducer using a pair of superconducting microwave cavities has been developed for use with cryogenic gravitational radiation antennas. Pumped by a 9.7-GHz SCSO, the cavities convert mechanical vibration into microwave sidebands which, after demodulation, reproduce the low-frequency signal. For the performance test of the transducer system, the cavities were mounted on a 15-kHz prototype disk antenna at 4.2 K. A transducer noise temperature of 23 mK was obtained at the antenna frequency, and hence a quantum noise number of 3.4×104.

Superconducting inductance-bridge transducer for resonant-mass gravitational-radiation detector.

The sensitivity of cryogenic gravitational-radiation detectors is presently limited by the performance of the transducers. A superconducting ac-pumped inductance bridge is proposed as a new transducer for resonant-mass gravitational-radiation detectors. The impedance matrix of the transducer is computed to determine the input, output, and transfer characteristics of the electromechanical system. It is shown that the dissipative forces exerted on the proof mass by the bridge circuit through the two sidebands cancel each other almost exactly so that the Brownian-motion level is nearly unaffected by the electric sensing circuit. This implies that an effective energy coupling coefficient near unity could be used without being limited by the electrical Nyquist noise. With the parametric up conversion of the signal, the inductance bridge can be coupled to a nearly quantum-limited dc superconducting quantum interference device (SQUID). The sensitivity of the gravitational-radiation detector employing the new superconducting transducer is computed as a function of transducer parameters. It is shown that the proposed transducer, with modest values for its parameters, is capable of matching a high-Q gravitational-radiation antenna, cooled to 50 mK, to a nearly quantum-limited dc SQUID.

A superconducting gravitational radiation antenna

In this paper we describe the superconducting gravitational radiation antenna being developed at the University of Western Australia (UWA) with particular reference to its high Q properties and the low loss mechanical filter used to support it. Recent measurements of the acoustic quality factor, Q, of the fundamental longitudinal mode of the bar are reported. It is shown that the Q is sufficiently high that it will not contribute significant noise to the antenna until the transducer becomes 'quantum limited'. We also report measurements on a smaller sample down to 0.4 K in which we observe that Q-1the acoustic loss, decreases exponentially with T-1between 2 K and 0.4 K.

Tapered cylinder antenna for gravitational radiation: Design and tests of a prototype

In an effort to increase the coupling between a gravitational radiation antenna and transducer the ends of a small cylindrical prototype antenna were tapered to magnify the end motion by a factor of 20. Flexural rigidity was maintained by tapering the inside of the cylindrical antenna. The algorithm used to calculate the taper is described. Experimental tests on the prototype antenna confirm the correctness of the algorithm. Results thus obtained indicate that much larger amplification is possible in full-scale antennas. The consequent decrease in the noise temperature is shown to be sufficient to improve the sensitivity of a resonant-mass gravitational radiation detector by at least an order of magnitude. As a result of the stronger coupling, the bandwidth is also increased.

Coupling of oscillation modes in an antenna for gravitational radiation

The energy transfer between two low-frequency eigenmodes of an antenna for gravitational radiation is studied at room temperature. No recognizable coupling of the modes has been found in equilibrium noates.

Low-dissipation support for a gravitational radiation antenna

We describe a support for the University of Rochester gravitational wave detector. The support is a two-stage filter with springs made of aluminum and a brass intermediate mass. With this support we have measured a mechanical quality factor for the fundamental mode of a 200-kg aluminum cylinder of 2.2×107 at 2302 Hz at 4.2 K. The filter attenuates vibrations by −130 dB at this frequency.

Parametric detector as a tunable antenna for continuous gravitational radiation

A way of using Weber-type antennas as tunable detectors of gravitational radiation from pulsars is described. Preliminary laboratory tests on the feasibility of such an instrument give encouraging results.

Ultra-low phase noise superconducting-cavity stabilised microwave oscillator with application to gravitational radiation detection

A superconducting-cavity stabilised oscillator has been constructed which combines active and passive stabilisation of a 9.6 GHz klystron to obtain a phase noise power spectral density between -170 dB Hz-1 and -180 dB Hz-1 at 5 kHz from the carrier, which represents about 40 dB improvement over the state-of-the-art. The device has been developed for use as a low noise pump for a superconducting parametric upconverter transducer on a gravitational radiation antenna. An RF modulated reflex klystron is actively locked to a TE011 niobium cavity operated at 2K with a loaded Q approximately 108. Power is extracted from the cavity which acts as a high Q filter.

A prototype back-action evading transducer suitable for gravitational radiation antennae

This paper describes a practical configuration for a back-action evading motion transducer suitable for use on Weber-type gravitational radiation antennae. Tests on a prototype are described, noise sources are discussed and realistic sensitivity limits are estimated.

Search for correlations between the University of Maryland and the University of Rome gravitational radiation antennas

Results are presented for analyses of the outputs of gravitational radiation antennas in Rome and in Maryland during July 1978. These data give evidence for an external background exciting both antennas.

Quality factors of a three-mode 50-kg gravitational radiation antenna at liquid helium temperature

A three-mode 50-kg gravitational radiation antenna has been tested in the temperature range 5–15 K. Acoustic losses in the Al–Nb system are estimated. Projections are made for the quality factor of each mode of a 1500-kg antenna. The fluctuations resulting from the thermal noise sources associated with the projected mechanical damping are estimated at 1.5×10−5 K in a system at 0.05 K.

Status of the Stanford gravitational wave experiment

Abstract The low temperature gravitational radiation antenna under development at Stanford has now been operating for about 1 year. During this time the system has been completely evaluated and 1250 hours has been spent taking data. The antenna noise temperature has been measured at 10 mK and the sensitivity in 10−1 GPU.

Low frequency antenna for gravitational radiation

We report on a resonant antenna for gravitational radiation at ω 2π = 44 Hz . The 14 kg aluminum antenna works in a torsional vibration mode and has a decay time τ = 1.4 × 10 5 s , namely, a quality factor Q = 4.0 × 10 7, at 4 K.

Low-noise temperature gravitational-radiation antenna-transducer system

A noncontacting 10 GHz re-entrant cavity transducer, capable of detecting displacements of 10−15 cm per Hz1/2 in the kilohertz frequency range, has been used on a magnetically levitated niobium gravitational-radiation antenna at 4.2 K. This sensitivity corresponds to a system effective noise temperature of about 40 mK, which is significantly lower than previous systems operated to date.

Observation of well-behaved noise and fluctuations in a gravitational-radiation antenna at liquid-helium temperatures

A 134-kg aluminum gravitational-radiation antenna instrumented with a resonant capacitive sensor and mounted on a new multistage suspension system has been tested. Well-behaved thermal noise and fluctuations have been observed. The system fluctuation temperature was 0.51 K, in close agreement with the predicted value.

Progress in the Development of High Sensitivity Gravitational Radiation Antennas

This paper reviews the development of gravitational radiation antennas from the pioneering work of J. Weber during the 1960s to the present day. Major problems stilI to be overcome are outlined,and prospects for the detection of gravitational radiation from astrophysical sources are discussed. Major emphasis is placed on Weber bar antennas, with spacecraft Doppler ranging and laser interferometer antennas discussed briefly. (As this review is intended primarily for non-specialists, no attempt is made to cite all workers in the field.)

Application of flux trapping in hard superconductors to magnetic shielding and magnetic levitation

A thermally switched magnetic shield which can both shield against and trap magnetic fields is described. The shield, consisting of a NbTi sheet, can trap stably fields of up to 0.3T, and shield against fields of up to 0.35 ± 0.05 T, when the in superconducting state It provides large attenuation of alternating magnetic fields in the presence of a steady trapped field. It is shown to significantly reduce the eddy current damping of the mechanical vibration of a superconducting sample in a magnetic field, by shielding nearby normal metal surfaces. A specific application to magnetic levitation of gravitational radiation antennae is discussed.

Electromechanical Tuning of Resonant Antennas for Gravitational Radiation

The frequency of resonant antennas for gravitational radiation can be tuned by application of an electromechanical force which modifies the effective force constant of the antenna structure associated with its deformation. A theoretical analysis of and experimental checks on the tuning devices based on this principle are presented.

Quantum limits on resonant-mass gravitational-radiation detectors

The methods of quantum detection theory are applied to a resonant-mass gravitational-radiation antenna. Quantum sensitivity limits are found which depend strongly on the quantum state in which the antenna is prepared. Optimum decision strategies and their corresponding sensitivities are derived for some important initial states. The linear detection limit (${E}_{min}\ensuremath{\sim}\ensuremath{\hbar}\ensuremath{\omega}$) is shown to apply when the antenna is prepared in a coherent state. Preparation of the antenna in an excited energy eigenstate or in a state highly localized in position or momentum space leads to increased sensitivity. A set of minimum-uncertainty states for phase-sensitive detection is introduced.