SQUID developments for the gravitational wave antenna MiniGRAIL

We designed two different sensor SQUIDs for the readout of the resonant mass gravitational wave detector MiniGRAIL. Both designs have integrated input inductors in the order of 1.5 muH and are planned for operation in the mK temperature range. Cooling fins were added to the shunt resistors. The fabricated SQUIDs show a behavior that differs from standard DC-SQUIDs. We were able to operate a design with a parallel configuration of washers at reasonable sensitivities. The flux noise saturated to a value of 0.84 muPhi0/radicHz below a temperature of 200 mK. The equivalent noise referred to the current through the input coil is 155 fA/radicHz and the energy resolution yields 62 h

An automated and versatile ultra-low temperature SQUID magnetometer

We present the design and construction of a SQUID-based magnetometer for operation down to temperatures T = 10 mK, while retaining the compatibility with the sample holders typically used in commercial SQUID magnetometers. The system is based on a dc-SQUID coupled to a second-order gradiometer. The sample is placed inside the plastic mixing chamber of a dilution refrigerator and is thermalized directly by the 3He flow. The movement though the pickup coils is obtained by lifting the whole dilution refrigerator insert. A home-developed software provides full automation and an easy user interface.Comment: RevTex, 10 pages, 10 eps figures. High-resolution figures available upon reques

Sensitivity of the spherical gravitational wave detector MiniGRAIL operating at 5 K

We present the performances and the strain sensitivity of the first spherical gravitational wave detector equipped with a capacitive transducer and read out by a low noise two-stage SQUID amplifier and operated at a temperature of 5 K. We characterized the detector performance in terms of thermal and electrical noise in the system output sygnal. We measured a peak strain sensitivity of $1.5\cdot 10^{-20} Hz^{-1/2}$ at 2942.9 Hz. A strain sensitivity of better than $5\cdot 10{-20}Hz{-1/2}$ has been obtained over a bandwidth of 30 Hz. We expect an improvement of more than one order of magnitude when the detector will operate at 50 mK. Our results represent the first step towards the development of an ultracryogenic omnidirectional detector sensitive to gravitational radiation in the 3kHz range.Comment: 8 pages, 5 figures, submitted to Physical Review

Development of a transducer for MiniGrail

Abstract We are developing a two-mode inductive resonant transducer for MiniGrail. We report several quality factor measurements, down to 4.2 K, performed on a scaled size resonator in different conditions: when suspended from a wire and when clamped, by thermal contraction techniques, into a hole of a sphere of 150 mm diameter and 14 kg mass. Q-factor measurements of a first resonator prototype at 4.2 K for MiniGrail are also presented. Finally, a fabrication process for a Nb film pick-up coil is described

GRAIL, an omni-directional gravitational wave detector

A cryogenic spherical and omni-directional resonant-mass detector proposed by the GRAIL collaboration is described.Comment: 5 pages, 4 figs., contribution to proceedings GW Data Analysis Workshop, Paris, nov. 199

MiniGRAIL progress report 2004

The MiniGRAIL detector was improved. The sphere was replaced by a slightly larger one, having a diameter of 68 cm (instead of 65 cm), reducing the resonant frequency by about 200 Hz to around 2.9 kHz. The last four masses of the attenuation system were machined to increase their resonant frequency and improve the attenuation around the resonant frequency of the sphere. In the new sphere, six holes were machined on the TIGA positions for easy mounting of the transducers. During the last cryogenic run, two capacitive transducers and a calibrator were mounted on the sphere. The first transducer was coupled to a double-stage SQUID amplifier having a commercial quantum design SQUID as a first stage and a DROS as a second stage. The second transducer was read by a single-stage quantum design SQUID. During the cryogenic run, the sphere was cooled down to 4 K. The two-stage SQUID had a flux noise of about 1.6 μ0 Hz−1/2. The detector was calibrated and the sensitivity curve of MiniGRAIL was determined

MiniGRAIL, the first spherical detector

Abstract An overview is given on the possibilities of building low cost omni-directional gravitational wave detectors using resonant spheres. Sensitivity curves of arrays and xylophones of spheres fabricated from different materials show that spherical detectors can be competitive with the large interferometers at frequencies above 1 kHz, with the additional advantage of being omnidirectional and being able to determine the direction and polarization of the gravitational wave. MiniGRAIL is the first spherical resonant detector, being built at the Kamerlingh Onnes Laboratory of Leiden University in the Netherlands. The detector is planned to operate at a temperature of about 20 mK and will have a quantum limited strain sensitivity for a burst signal of the order of 4 × 10 −21 . We present the progress concerning cryogenics and transducer development. PACS numbers: 04.80. Nn, 95.55.Y

Melting process and interface instability of highly magnetized solid 3He: Role of the magnetization gradient

Theoretical PhysicsQuantum Matter and Optic