It is based on the working principle of a multistage-pendulum where the mirror is the delicate last stage payload and the suspension point is ground connected through a three legs structure conceived on the working principle of an Inverted Pendulum. In the photo here attached (left side) the upper part of a Superattenuator is visible together with the mechanical filters used to form the multistage-pendulum. The design of the Superattenuator has been centered on the idea to extend the detection bandwidth in the low frequency region (below 100 Hz) because many astrophysical sources are expected to emit mainly low-frequency Gravitational Waves. Any element included in the Superattenuator chain has been deeply studied and realized in such a way to lower, as much as possible, the frequency detection threshold of the whole ground based interferometer.

Galli & Morelli started the collaboration with the INFN Pisa Group involved in the development of this sophisticated electro-mechanical device since the prototyping phase, participating in a long and fruitful process during which the final technical design was conceived by the INFN experts. This relationship has been of great importance for our workshop because the Galli & Morelli personnel had the opportunity to acquire specific “know-how” in the contest of precision mechanics components production to be operated in Ultra High Vacuum environment.

Each mechanical filter included in the multi-stage pendulum chain represents a second order low-pass filter to suppress the seismic noise transmission to the mirror level. It has been designed with a drum shaped body on the bottom part of which a set of pre-bent triangular blades are mounted. The pendulum chain is formed connecting each filter to the next one by using thin suspension wires so that the load of each stage is hung to the tip of the blades that assume a flat position. The blades and the thin wires, machined at the Galli & Morelli workshop with two nail heads on both sides of each section, are made of Maraging alloy an ultra high strength steel. To this purpose there has been an important technological transfer between the INFN Pisa personnel and our technicians at Galli & Morelli, to acquire some competences concerning its machining and their thermal and surface treatments.

A bottom view of a typical experimental set-up of the top stage filter is visible in the photo above, where ten triangular blades in working conditions (flat position) are showed.

In the recent years the VIRGO Collaboration worked on an intensive upgrade program to transform the first generation instrument into a detector of second generation able for a direct observation of Gravitational Waves on Earth. This has been done improving the design sensitivity of a factor ten with a corresponding increment of a factor one thousand in the observational volume of the Universe. Thanks to these activities the new Advanced VIRGO interferometer will be operated within an international network together with the other two large interferometers of the LIGO Scientific Collaboration (installed in USA) with a common intent to perform Gravitational Waves direct observations and to localize their source in the sky.

Even this time Galli & Morelli has been honored to be among the selected workshops involved in the construction of different mechanical components installed on the new interferometer. From now on our personnel will feel closer to the group of scientists involved in operating the Advanced VIRGO interferometer with the intent to observe the Universe through the Gravitational Waves astronomy.