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. 2001600Hz). -> 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. 

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