AURIGA: the test facility

The Transducer Test Facility

In order to improve the sensitivity of the detector, the AURIGA collaboration is working on some R&D projects focused on the redesign of the transducer-amplifier chain. Obviously, before implementing the new devices on the detector they must be tested in an experimental setup that mimics the final one: the detector itself cannot be used as a transducer-amplifier bench test!

To this end the AURIGA collaboration developed the Transducer Test Facility (TTF) where to test readouts in a configuration suitable for the integration on the main detector. In particular the TTF should allow one to:

operate the readout at the same temperature as it would operate in AURIGA (approximately 0.1K). -> The TTF is thus equipped with a dilution refrigerator.
reduce mechanical (e.g. seismic) noise at 0.1K so that it does not overcome the readout noise (e.g. transducer thermal noise). -> An overall mechanical attenuation of at least -160dB is required for frequencies around 1kHz (the frequency range of interest for AURIGA).
not to introduce spurious mechanical resonances (e.g. due to the mechanical suspension) in the frequency range of interest (i.e. 200÷1600Hz). -> Further constraints on the suspension design.
make fast (order of one week) thermal cycles because readout optimization requires many cryogenic runs.
have an experimental chamber wide enough to house the readout (transducer + amplifier). Typical linear dimension must be of the order of 30cm.

With these requirements in mind the TTF was designed via a Finite Elements analysis and then machined. Presently it appears as in the following 3-dim drawing:

Click here for an enlarged image (110KB jpeg file).

Terms in the above picture are explained and discussed in the following:

Sylomer ®: soft rubber spring with high internal friction: it provides the first room-temperature isolation stage;
Honeycomb: very light and high strength material plate with internal overdamped resonances;
Dewar: liquid Helium vessel that houses the experimental chamber;
Room temperature suspension: TTF support. It provides also for a mechanical isolation stage assuring -65dB at about 1kHz;
IVC: acronym for Internal Vacuum Chamber. It is the experimental chamber that houses the last suspension stage and the devices (e.g. transducer and amplifier) to be tested;
Mixing chamber: coldest part of the dilution refrigerator. The measured lowest temperature measured in the TTF is 15mK (without any thermal load).
Low temperature suspension: the last mechanical suspension stage. The upper part is connected by a stainless steel spring to the IVC upper flange; the last annular mass holds the transducer by means of copper springs that provide also for the thermal link with the mixing chamber. The isolation is measured to be -50dB at 1kHz for each spring: the inferred overall isolation is thus -230dB at 1kHz.

Glossary