AURIGA

Collaboration:

- Ferrara, Firenze, LNL, Padova e Trento

Laboratory: Legnaro National Laboratory of INFN

National Responsible: M. Cerdonio (Padova)

1. Goal of the experiment

The AURIGA experiment (the acronym stands for Ultracryogenic Resonant Antenna for the Gravitational Astronomical Investigation) aims to the direct detection of impulsive gravitational waves originating in astrophysical phenomena (supernovae explosion, final part of coalescing of Neutron Star or Black Hole binary systems) in our and nearest galaxies.

More on the experiment…

2.

Activities during 2002

The scientific program of AURIGA runs on 4 different, but interlinked routes, levels: main detector hardware development, data analysis , R&D on resonant capacitive transducer with SQUID read-out and R&D on resonant optical Fabry-Perot cavity read-out, proposals for wideband acoustic gw detectors.

Main detector: after the cryogenic failure in October '99, we have modified fully the cryogenic component of suspension system and a lot of cryogenic component linked to the dilution refrigerator with the aim to increase the duty cycle of the detector. The systems are assembled and working in the 600 Hz-1600 Hz band free of spurious frequencies. We have built and tested a new cryogenic vessel integrated inside the main cryostat with increased autonomy (100 l of liquid helium) and with higher cryogenic reliability. The restart of the operation of the detector has been postponed, to allow to incorporate all the upgrades, including the new suspensions (not originally planned).

Data analysis: two main results have been achieved. The new data acquisition and analysis system of AURIGA based on "frames" has been developed and is under tests on the data produced by the test facility of transducers. The analysis of the IGEC 1997-2000 observation has been completed and new upper limits on the rate of burst gravitational waves has been set. To this aim new analysis methods for coincidence searches among many detectors have been developed and implemented. In addition, we investigated the implementation of coherent methodologies of data analysis for a network of detectors and for the filtering of gw signals slowly sweeping in frequency by means of Wigner-Ville transforms.

R&D on capacitive transduction chain: with the ultracryogenic test facility in full operation, the tests on the new capacitive transducer equipped with a double stage SQUID amplifier is almost concluded. Tests have been performed in the temperature range 1,5-4,2 K demonstrating an energy sensitivity of about 300 quanta at the transducer resonance frequency, with the two mode (mechanical and electrical) completed tuned to reach the better energy coupling, with this solution AURIGA will be the first detector working with a three tuned mode configuration.

Some details follow:

> Amplifier systems based on double stage SQUIDs: the amplifier system based on the Quantum design SQUID sensors has been operated at liquid Helium temperature in a regime of strong coupling to a high Q resonant load and with improved noise performances: 120 hbar at 1.3 K and 11kHz. In these condition we were able to perform the very relevant measurement of the SQUID back-action noise. The coupling of the amplifier to the resonant load and the system rejection to external noises has been improved as well. A great effort has been focused on the development of a SQUID electronics and we achieved significant progresses on the dynamic range and on the stability of the double stage SQUID system. The experimental study on different amplifiers based on different SQUID sensors started as well, in particular to study feedback chains to stabilize their operation. We developed a few wiring configurations to charge the capacitive transducer without affecting the high electrical Q of the LC resonators which acts as an impedance matching stage to the SQUID amplifier.

> Implementation of a new design of various components allows to avoid mechanical disturbances in the bandwidth 800-1200 Hz.

> Operation of the complete transduction chain:

> We achieved a complete calibration in energy of the system through direct measurement of transfer functions.

> We defined a cleaning procedure for conditioning at room temperature the surface of the transducer, which allows to reach high electric field > 5MV/m.

R&D on resonant optical Fabry-Perot cavity read-out: we have performed a series of tests at cryogenic temperature on the single components of the optical readout and chosen the most suitable optical fibers. We have designed new suspensions and temperature shields for operating the room-temperature bar, equipped with the optical read-out, at cryogenic temperatures. The upgrade is in progress. The test of the resonant transducer in the cryogenic test facility has been postponed to allow completing the optimization of the capacitive SQUID transducer, needed for the next AURIGA run. We have proposed and studied theoretically a novel kind of optical cavity (`Folded Fabry-Perot') which allows to overcome the problem of the limited sensing area of the transducers, thus lowering the effect of thermal noise and back-action. Such a device would optimize the sensitivity of advanced massive detectors up to the quantum limit. The sensitivity is limited by thermal noise and we were able to show that due to the inhomogeneous losses the normal mode expansion fails. The laser system and the two stable cavities have also been employed for testing the model of photothermal effect proposed from people of the group.

Studies on wideband acoustic gw detectors: we have proposed a new schemes for the operation of transducer systems for acoustic gravitational wave detectors based on the dual concept and with very wide frequency bandwidth. These designs are able to select the deformations of the antennae with the right symmetry for gw detection and therefore reject the mechanical thermal noise contributed by resonant modes which are not sensitive to gw. In addition, these schemes can give a reduction of the back-action noise within the detector bandwidth.

As a summary, the following achievements have been obtained:

New data analysis for both on-line and off-line data: (100%) Currently under test.

Start of the operation of an ultracryogenic test facility for coupled dc SQUIDs in Trento: It has not been possible to start operation in 2002 because the He3-He4 dilution refrigerator has been delivered by the supplier in Jan.2003, with an unexpected delay of more than one year.

Data taking of the detector at T=2K with pulse sensitivity of 0.1 mK and bandwidth of 10 Hz:(40%) Data taking did not start in 2002. We have been able to complete the hardware upgrades of the detector (suspensions, 2K cryogenics) and the capacitive readout is under final tests on the transducer test facility.

Noise measurements of the new optical transducer operating at cryogenic temperatures: (75%) We have completed the cryogenic tests on the single optical components and chosen the most suitable optical fibers. The updating of the room-temperature bar for cryogenic operation is still in progress. The test of the resonant transducer in the cryogenic test facility.

Data taking at T=0.2 K with pulse sensitivity of 0.01 mK and bandwidth of 30 Hz.: Since the work on the preparation of the T=2K run is still in progress, no activity has been focused in 2002 for this milestone.

Milestones 2003

Back-Action measurements of SQUID amplifier strongly coupled to the ultracryogenic temperatures | 31-05-2003
Debugging and starting scientific run of Auriga detector able to reach an energy burst sensitivity of 0.1 mK and a bandwidth of about 10 Hz | 31-07-2003
Getting ready a protocol about a new collaborative data analysis with the interferometers: TAMA, Virgo, Geo, Ligo. | 31-12-2003
Debugging of the optical transducer in the cryogenic environment ready to use in the bar | 31-12-2003

3. INFN contribution to the experiment in terms of manpower and financial support

Manpower: 21 researchers (13 FTE), 5 technicians (1.5 FTE) and the support from the mechanics workshop of LNL and the electronic workshops of the Padova Section.

Budget for the Year 2003: 2.1% of the CSNII total budget

4. P ublications in refereed journals (Year 2002): 9

5. Number of conference talks (Year 2002): 14

6. Number of undergraduate and doctoral thesis on the experiment:

- n.1 Ph.D
- n.3 Laurea diplomas.

7. Leadership roles and primary responsibilities in the experiment

- Spokesperson: member of GWIC, PANAGIC, LIST and of the Panel LIGO Site Visit at the MIT
- Padova section leading about up-grading of the main detector and R&D transduction chains in the room temperature bar and ultracryogenic test facility
- LNL and Trento leading in the acquisition and analysis data, G.A.Prodi had a propulsive role in the IGEC “task force” for the joint coincidence analysis.
- Trento and IFN-CNR ITC collaboration SQUID and LC resonators;
- Florence Section optical read-out
- Ferrara Section astrophysical sources.

8. Innovative instruments

The Auriga group develops specific technologies:

- Characterization of ultrasensitive SQUID (below 100 quanta).
- Compact mechanical attenuation system for ultracryogenic environments
- Fast data acquisition and analysis on line, data validation against non-stationary and non-modeled noise.
- Ultracryogenic test facility for studies on quanta behavior of amplifier and mechanical oscillators.
- Optical read-out at shot noise level at 1 kHz.

9. Competing experiments.

The challenge towards the first detection of g.w. has produced between all the project world wide a friendly competition and extensive exchange of scientific information for the methods and the technologies and, most important, collaboration for the data analysis and for the long-term strategies (no single detector would be able to perform significant searches). IGEC is in fact the collaboration effort of all the “bar” project. As for the interferometers detectors, the acknowledged view is that the initial interferometers and “bar” will work complementary together. “Advanced” resonant detectors (hollow spheres, dual systems etc.) will as well complement “advanced” interferometers. The Gravitational Wave International Collaboration GWIC (Cerdonio is a members as Auriga spokesperson) promotes coordination and collaboration among all the project to ensure maximal chances or early first detection and continuing observation.

10. International committee which has reviewed the experiment