Print version ISSN 0103-9733
Braz. J. Phys. vol.32 no.4 São Paulo Dec. 2002
The Gravitational Wave Detector "Mario Schenberg": Status of the Project
O.D. Aguiar1, L.A. Andrade1, L. Camargo Filho 4, C.A. Costa1, J.C.N. de Araujo1, E.C. del Rey Neto1, S.T. de Souza2, A.C. Fauth4, C. Frajuca5, G. Frossati7, S.R. Furtado1, V.G.S. Furtado1, N.S. Magalhães6, R.M. Marinho Jr.3, E.S. Matos1, M.T. Meliani1, J.L. Melo1, O.D. Miranda1, N.F. Oliveira Jr.2,K.L. Ribeiro1, K.B.M. Salles1, C. Stellati3, W.F. Velloso Jr.1
1. Instituto Nacional de Pesquisas Espaciais - Divisão de Astrofí sica, São José dos Campos, S.P., Brazil
2. Universidade de São Paulo - Instituto de Fí sica, São Paulo, SP, Brazil
3. Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, Brazil
4. Universidade Estadual de Campinas - Instituto de Física, Campinas, SP, Brazil
5. Centro Federal de Ensino Tecnológico de São Paulo, São Paulo, SP, Brazil
6. Universidade Bandeirante de São Paulo, São Paulo, SP, Brazil
7. Leiden University - Kammerlingh Onnes Laboratory, Leiden, The Netherlands
Received on 31 January, 2002
The first phase of the Brazilian Graviton Project is the construction and operation of the gravitational wave detector Mario Schenberg at the Physics Institute of the University of São Paulo. This gravitational wave spherical antenna is planned to feature a sensitivity better than h = 10-21 Hz-1/2 at the 3.0-3.4 kHz bandwidth, and to work not only as a detector, but also as a testbed for the development of new technologies. Here we present the status of this detector.
I The project
The antenna will weight about 1150kg , which is only a factor of 2 less massive than existent antennas. By cooling it to much lower temperatures (15-20 mK), however, and by making it spherical (omnidirectional), we expect a considerable improvement in sensitivity .
The project will be divided in two phases: GRANTED phase and detector phase. In the Gravitational Radiation ANtenna TEchonology Demonstration phase (GRANTED), we will test the following aspects:
a) the feasibility to construct a heavy ( ~ 1150kg) copper-aluminum (94%-6%) spherical mass, which presents a high (Qm > 107) mechanical Figure of Merit at 20mK ;
b) the feasibility to quickly (less than a week) cool such a mass down to 20mK ;
c) the feasibility to extract and analyze data from a transducer attached to the spherical surface;
d) the feasibility to protect such a spherical mass from laboratory and environment vibrations by the use of designed vibration isolation systems for the mass suspension, the dilution refrigerator and the transducer wiring.
After completing the technology demonstration phase (GRANTED), we intend to construct and place a set of high sensitivity transducers attached to the surface of the sphere, transforming the above prototype into an effective gravitational wave detector, the Mario SCHENBERG detector, in the 3.0-3.4 kHz frequency bandwidth.
II The scientific goals of the present detector
A 65cm-diameter Cu-Al (94%-6%) antenna will be covering the 3.0-3.4 kHz bandwidth, which has astrophysical importance. It would be operating in coincidence with the Dutch Mini-GRAIL and the Italian SFERA antennas, and some large laser interferometer detectors, which can also cover such high frequencies with similar sensitivities .
The astrophysical events that we anticipate as probable candidates for detection in the 3.0-3.4 kHz region, where the SCHENBERG detector will be sensitive, are : core collapse in supernova events; neutron stars going to hydrodynamical instability; quakes and oscillations of neutron stars (f modes) induced by the falling of matter in binary systems; excitation of the first quadrupole normal mode of ~ 3.8M black holes; coalescence of ~ 1.9M neutron stars and/or black holes.
We also can speculate some "exotic" sources such as: rotation of bosonic or strange matter stars at ~ 1.6kHz; inspiralling of mini-black hole binaries.
III The Schenberg group
The group is divided in six major subjects:
1) Cryogenics, with Prof. Nei Oliveira Jr. (Co-PI), Prof. Giorgio Frossati (Co-PI), Karla Salles (Master student), Sérgio Furtado (Master student), and Sérgio de Souza (Master student);
2) Astrophysical Sources and Gravitation, with Dr. José C.N. de Araujo, Dr. Oswaldo D. Miranda, Dr. Mara Meliani, and Dr. Edgard del Rey Neto ;
3) Vibration Isolation, with Dr. Walter Velloso Jr. and José Melo (Ph.D. student) ;
4) Transducers, with Dr. Carlos Frajuca, Kilder Ribeiro (Ph.D. student), and Luiz Andrade (Ph.D. student);
5) Cosmic Ray Detection Hardware, with Dr. Anderson Fauth and Lúcio Camargo Filho (undergraduate student);
6) Data Analysis, with Dr. Rubens Marinho Jr., Dr. Nadja Magalhães, Claudemir Stellati (Ph.D. student), César Costa (Master student), Valéria Furtado (Master student), and Emí lio Matos (Master Student) .
The Brazilian group is developing this project in collaboration with the Dutch group and all four major groups operating cryogenic resonant mass antennas (ALLEGRO, NAUTILUS & EXPLORER, AURIGA and NIOBÈ). It also receives collaboration from researchers and professors working at some other Brazilian institutions and universities and at some laser interferometer projects (LIGO, VIRGO, and LISA).
IV The status of the detector
IV.1 Site preparation
The site preparation at the University of São Paulo is under the coordination of N. Oliveira Jr., and is almost completed. A pit has been constructed in one of his laboratory rooms, where the detector will be located. There is one hydraulic piston inside a concrete column at each of the four corners of this pit. These pistons form a hydraulic system that can lift up to 2m a reinforced 4-ton concrete base, on which the detector will be assembled. A crane has been installed on the top of a sliding structure connected to the upper part of the room walls. This crane together with the hydraulic system will provide some flexibility for the detector assembly.
IV.2 Cryogenic chambers
The cryogenic chambers have been designed by G. Frossati and collaborators. They will be shipped from KADEL (USA) in October of 2001, and will be assembled on the concrete base as soon as they arrive at the University of São Paulo.
Frossati has also designed the dilution refrigerator that is going to be used in the detector.
IV.3 Vibration isolation system
The vibration isolation system that will be used in the Mario Schenberg detector is the product of a technology developed by various gravitational wave detector groups in a few decades of experience. The designed one uses C springs that were proposed by Italians collaborators. Melo and Velloso have done some detailed calculations using this design and a finite element software (NASTRAN). They were able to design a vibration isolation system free from resonances close to the 3.0-3.4kHz frequency band. This system, that will be inside the cryogenic chambers, together with a room temperature vibration isolation system very similar to the one used by the ALLEGRO detector, will be able to attenuate more than 360 dB the vibrations coming though the antenna suspension system.
This system will be cast at ITALBRONZE (Brazil), and will be delivered by the end of 2001.
A first spherical antenna has been cast by ITALBRONZE (Brazil) at the beginning of 2001. It was sent to the Dutch group for testing.
The Schenberg antenna will be cast at ITALBRONZE by the end of 2001.
We plan to use a set of seven two-mechanical-mode parametric transducers pumped at about 10GHz for monitoring the first monopole (one transducer) and first five quadrupole (six transducers) modes of the spherical antenna. This will be done in collaboration with the Australian group and with other groups in Brazil.
The first cryogenic run is schedule to the beginning of 2002 and the first transducer test to about six months later. Finally, we plan to put the detector in a commissioning phase sometime in 2003.
This work has been supported by FAPESP (under grants No. 1998/13468-9, 1996/01872-4, 1997/06024-4, 1999/10809-2, 2000/10374-5, 2001/04189-3, 2001/04086-0, 2001/04226-6), CNPq (under grants No. 300619/92-8 and AVG/450994/01-5), CAPES and INPE/MCT.
 Proposal submitted in November of 1998 and approved by FAPESP in April 2000
 The initial proposal was a Cu-Al(6%) 800kg buckyball antenna. However, in common agreement with the Mini-GRAIL and SFERA groups we decided to change it to a Cu-Al(6%) 1150kg spherical antenna. The high frequency operation of the antenna requires that the transducers be clamped at the antenna surface instead of bolted, therefore there would be no need for flat surfaces (normally required for bolting transducers) and so, for a polyhedron shape antenna. The natural spherical shape also has more mass (more cross section to the waves). The diameter was increased too (from 60cm to 65cm) because we had more room in the cryogenic chambers and because the 3.0-3.4kHz frequency window seemed more interesting from the astrophysical point of view of the gravitational wave sources listed on § 2 compared to the original 3.9-4.3kHz frequency one. For example, for hydrodynamical instabilities of neutrons stars, Houser (1998 Mon. Not. R. Astron. Soc. 299, 1069) showed that a frequency band below 3.5kHz would have more chances to see a stronger signal
 Forward, R. L. 1971 General Relativity and Gravitation 2, 149. [ Links ]Wagoner, R. V. and Paik, H-J. 1977, Proceedings of the Academia Nazionale dei Lincei, International Symposium on Experimental Gravitation, Pavia, Italy, Sept. 1976, p.257. [ Links ]Johnson, W. W. and Merkowitz, S. M. 1993 Physical Review Letters 70, 2367. [ Links ]Coccia, E. 1997, 14th International Conference on General Relativity and Gravitational, Florence, 1995, World Scientific, Singapore, pp. 103. [ Links ]Waard, A. and Frossati, G. 2000, Proceedings of the Third Edoardo Amaldi Conference on Gravitational Waves, 1999, Pasadena, California. AIP Conference Proceedings. American Institute of Physics 523, 268 [ Links ]
 Frossati, G. et al. 1997, Proceeding of the First International Workshop of Omnidirectional Gravitational Radiation Observatory, São José dos Campos, Brazil, May 26-31, 1996, edited by W. F. Velloso, O. D. Aguiar, and N. S. Magalhães, World Scientific, Singapore, 179 [ Links ]
 This has already been demonstrated by the Dutch group (www.minigrail.nl) in 2001
 Proceedings of the Third Edoardo Amaldi Conference on Gravitational Waves, 1999, Pasadena, California. AIP Conference Proceedings. American Institute of Physics 523 (2000) [ Links ]
 Wagoner, R. V. 1984 Ap.J. 278, 345. [ Links ]Schutz, B. F. 1997, Relativistic Astrophysics and Gravitational Radiation, eds. J-A. Marck and J-P. Lasota, Cambridge Univ. Press. [ Links ]Anderson, N. and Kokkotas, K. D. 1996 Phys. Rev. Lett, 77 4134. [ Links ]Anderson, N.; Araújo, M. E. and Schutz, B. F. 1993 Class. Quantum Grav. 10, 757. [ Links ]Friedman, J. L.; Ipser, J. R. and Parker, L. 1989 Phys. Rev. Lett. 62 3015. [ Links ]Haensel, P.; Lasota, J-P. and Zdunik, J. L. 1999 preprint (astro-ph/9905036). Nakamura, T.; Sasaki, M.; Tanaka, T. and Thorne, K. S. 1997 Ap. J. 487 L139. [ Links ]Thorne, K. S. 1987, 300 Years of Gravitation, edited by S. Hawking and W. Israel, Cambridge Univ. Press, Cambridge, pp. 330. [ Links ]Harry, G. M.; Stevenson, T. R. and Paik, H-J. 1996 Phys. Rev. D54 2409 [ Links ]
 de Araujo, J. C. N.; Miranda, O. D. and Aguiar, O. D. 2001 Ap. J. 550 368. [ Links ]Meliani, M. T.; de Araujo, J. C. N. and Aguiar, O. D. 2000 Astron. Astrophys. 358 417. [ Links ]de Araujo, J. C. N.; Miranda, O. D. and Aguiar, O. D. 2000 Phys. Rev. D61 124015. [ Links ]Novello, M.; Lorenci, V. A.; Freitas, L. and Aguiar, O. D. 1999 Phys. Lett. A 254 245. [ Links ]Mosquera-Cuesta, H. J.; de Araujo, J. C. N.; Aguiar, O. D. and Horvath, J. E. 1998 Phys. Rev. Lett. 80 2988 [ Links ]
 Velloso Jr., W. F.; Melo, J. L. and Aguiar, O. D. 2000 Rev. Sci. Instrum. 71 2552 [ Links ]
 Magalhães, N. S.; Aguiar, O. D.; Frajuca, C. and Marinho Jr., R. M. 2001 Nucl. Instrum. Meth. Phys. Res. A457 175. [ Links ]Magalhães, N. S.; Aguiar, O. D.; Frajuca, C.; Marinho Jr., R. M. and Chiang, J. 2001 Nucl. Instrum. Meth. Phys. Res. (in press). Marinho Jr., R. M.; Magalhães, N. S.; Aguiar, O. D. and Frajuca, C. 2001 Phys. Rev. D (in press). Magalhães, N. S.; Johnson, W. W.; Frajuca, C. and Aguiar, O. D. 1997 Ap. J. 475 462. [ Links ]Magalhães, N. S.; Aguiar, O. D. and Frajuca, C. 2001 Phys. Rev. D (in press). Magalhães, N. S.; Aguiar, O. D. and Frajuca, C. 1997 Gen. Rel. Grav. 29 1511. [ Links ]Magalhães, N. S.; Johnson, W. W.; Frajuca, C. and Aguiar, O. D. 1995 Mon. Not. R. Astr. Soc 274 670. [ Links ]