P.J. Turner

Search for coincident excitation of the widely spaced resonant gravitational wave detectors EXPLORER, NAUTILUS and NIOBE

We report the search for coincidences among three resonant mass detectors: EXPLORER at CERN and NAUTILUS in Frascati of the Rome group and NIOBE in Perth of the UWA group. The three detectors have a sensitivity for short bursts of GW in the h ≈ 10−18 range, about one thousand times better in energy than Webers original detectors. The analysis is based on the comparison of candidate event lists recorded by the detectors in the period December 1994 through October 1996. The events have been obtained by applying a pulse detection filter to the raw data and using a predetermined threshold. Due to the different periods of data taking it was not possible to search for triple coincidences. We searched for coincidences between EXPLORER and NAUTILUS during the years 1995 and 1996 for a total time coverage of 1372 hours and between EXPLORER and NIOBE in 1995 for a coverage of 1362 hours. The results have been: a weak indication of a coincidence excess with respect to the accidental ones between EXPLORER and NAUTILUS and no coincidence excess between EXPLORER and NIOBE.

Laboratory tests of a mobile superconducting gravity gradiometer

Abstract We describe a gravity gradiometer designed to measure off-diagonal components of the earths gravity gradient tensor, and intended for airborne geophysical exploration. The instrument consists of an orthogonal pair of mass quadrupoles pivoted about a common vertical axis. Each quadrupole is a rectangular bar of niobium having square cross section and with integrally machined flexural micro-pivots. Superconducting niobium pancake coils form the basis of the SQUID based transducers and provide supplementary magnetic springs to enable matching of mechanical parameters.

A sapphire oscillator for VLBI radio astronomy

The authors present a sapphire oscillator with a long hold-time cryostat and helium recovery system to overcome the inherent difficulty of using this liquid-helium-cooled frequency standard at a remote site. The oscillator has been used as a frequency reference for very long baseline interferometry (VLBI) radio astronomy observations. Data are presented which show that the performance of the oscillator is superior to a rubidium standard in this application. While laboratory data have demonstrated a fractional frequency stability of about 9*10-15 for integration times between 1 and 300 s the VLBI frequency stability measurements in this case are limited by the signal-to-noise ratio in the correlated data.

Noncontacting microwave coupling to a cryogenic gravitational radiation antenna

Gravitational radiation detectors must detect extremely small displacements, and thus require elaborate vibration isolation systems to attenuate the surrounding environmental noise. Contacting electrical leads can provide a direct path that will short circuit the vibration isolation, and degrade the antenna Q factor. Noncontacting microstrip transceivers provide a practical means of electromagnetically coupling to a resonant bar gravitational antenna when a microwave transducer is used as a signal readout system. Two microwave patch antennas now operate as transceivers on the University of Western Australia’s 1.5 tonne niobium bar gravitational radiation antenna and are described in detail in this paper. This system allows improved vibration isolation without degradation of the acoustic Q factor of the niobium bar. Combined with a cryogenic amplifier, this system should achieve a reduction of 57 dB in the series noise power. This corresponds to a factor of 700 reduction in the effective displacement noise...

The University of Western Australia's resonant-bar gravitational wave experiment

The cryogenic resonant-mass gravitational radiation antenna at the University of Western Australia (UWA) has obtained a noise temperature of <2 mK using a zero order predictor filter. This corresponds to aIms burst strain sensitivity of 7x 10-19 . The antenna has been in continuous operation since August 1993. The antenna operates at about 5 K and consists of a 1· 5 tonne niobium bar with a 710 Hz fundamental frequency, and a closely tuned secondary mass of 0·45 kg effective mass. The vibrational state of the secondary mass is continuously monitored by a 9·5 GHz superconducting parametric transducer. This paper presents the current design and operation of the detector. From a two-mode model we show how we calibrate, characterise and theoretically determine the sensitivity of our detector. Experimental results confirm the theory.

Quality factor of polycrystalline Nb between 0.4 and 10 K

The audiofrequency mechanical quality factor of niobium has been measured in the temperature regime 0.4–10 K. The results show that below 2 K the acoustic lossQ−1 reduces exponentially asT−1 → ∞. The data imply that the activation energy for thermally activated relaxation losses is finite atT=0 and that arbitrarily highQ factors may be achievable at very low temperatures.

Niobium gravitational radiation antenna with superconducting parametric transducer

Abstract Progress and latest results on the development of a niobium gravitational radiation antenna are reported. An improved vibration isolation system has been installed and is currently under test. The previously developed transducer self-calibration procedure is summarized. We show that the power dependent microwave cavity Q limits the maximum achievable antenna-transducer coupling factor, β, and thus the maximum bandwidth of the antenna, B. The self-calibration procedure is combined with new data for the performance of the reentrant cavity transducer to determine the maximum β and B which can be achieved. Results given here show maximum values of β κ 0.04 and B κ 15 Hz.

Microwave signal processing for a cryogenic gravitational radiation antenna with a noncontacting readout

A modified version of the microwave signal processing system for the 1.5 tonne niobium bar gravitational radiation antenna at the University of Western Australia has been developed and tested during preparations for long‐term observation. Among the new features of the system are a noncontacting microwave coupling to the motion transducer, cryogenic low‐noise amplification, and automatic carrier suppression with improved long‐term stability.

Test of a model solar bakeout system for laser interferometer gravitational wave detectors

It is shown that simple, inexpensive solar energy technology can be used to bake large scale vacuum tubes intended for use in laser interferometer gravity wave detectors which are currently being planned in Europe, USA and Australia.

Simple sorption pumped 3He cryostat with temperature control

Abstract A charcoal sorption pumped 3He cryostat is described for temperatures down to 300 mK. The sorption pump speed is varied by varying its temperature to achieve temperature control and although the cryostat is one-shot in principle, the 3He can be recycled very rapidly and several cycles, giving a total of some eight hours operation, can be achieved with each liquid 4He fill of the cryostat main dewar.