On the Dilution Refrigerator Thermal Connection for the SCHENBERG Gravitational Wave Detector
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GENERAL AND APPLIED PHYSICS
On the Dilution Refrigerator Thermal Connection for the SCHENBERG Gravitational Wave Detector Fabio da Silva Bortoli1 · Carlos Frajuca1 · Nadja S. Magalhaes2 · Sergio Turano de Souza3 · Wilson Carlos da Silva Junior1 Received: 25 May 2020 © Sociedade Brasileira de F´ısica 2020
Abstract The resonant-mass gravitational wave detector SCHENBERG was designed by the Brazilian group Graviton to be sensitive to a central frequency nearing 3200 Hz and a bandwidth of 200 Hz. It has a spherical antenna weighing 1150 kg that is connected to the outer environment by a suspension system designed to attenuate local noise due to seism as well as other sources. Should a gravitational wave pass by the detector, the antenna is expected to vibrate. This motion will be monitored by six parametric transducers whose output signals will be digitally analyzed. In order to improve the sensitivity of the detector, it must be cooled down to the lowest possible temperature, and for this purpose a dilution refrigerator is planned to be implemented in the detector. It is known that such device produces vibration when operational, consequently introducing noise in the system. Using the finite elements method, this work investigates thermal connections between the dilution refrigerator and the sphere suspension that allow the detector to operate within its projected sensitivity. The finite elements method showed an attenuation of 240dB in the best-valued thermal connection. Keywords Gravitational wave · Gravitational wave detector · SCHENBERG detector · Dilution refrigerator
1 Introduction SCHENBERG is a resonant-mass gravitational wave (GW) detector that is expected to be reassembled in a new construction site at the National Institute for Space Research in Brazil. Its schematics is shown in Fig. 1, and it was disassembled in 2016 from its initial site, in which two runs took place and many technical improvements were implemented [1–4]. It has a central detection frequency nearing 3200 Hz and bandwidth around 200 Hz. Its antenna is a spherical mass weighting 1150 kg, with a diameter of 0.65 m and made of a copper-aluminum alloy (94% Cu and 6% Al) [5]. This solid sphere is isolated from seismic noise by a mechanical suspension system [6]. Fabio da Silva Bortoli
[email protected] 1
Departamento de Mecanica, Sao Paulo Federal Institute, Sao Paulo, SP, Brazil
2
Physics Department, Federal University of Sao Paulo, Diadema, SP, Brazil
3
Cruzeiro do Sul University / FATEC Prof. Miguel Reale, Sao Paulo, SP, Brazil
The detector operates with six electromechanical resonant transducers [7–11] connected to the antenna’s surface and distributed on it according to a half dodecahedron configuration [12–14]. Signals from the sensors are expected to yield the amplitude, polarization, and source direction of a passing gravitational wave. The SCHENBERG detector, when operational, would thus contribute to the worldwide effort to increasingly implement gravitational astronomy [15]. While the equipment is disassembled, inv
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