Acoustic System Development for Neutrino Underwater Detectors

Resumo

The main objective of this research is the design and development of two different underwater acoustic emitters aimed to the deep-sea KM3NeT neutrino telescope, more specifically for the Acoustic Positioning System (APS) and for the calibration of the acoustic neutrino detection technique. The KM3NeT project is a new optical-based deep-sea neutrino telescope, currently under construction. The main objectives of the KM3NeT telescope are the discovery and observation of high-energy neutrino sources in the Universe and the determination of the mass hierarchy of neutrinos. The KM3NeT detectors consist of three-dimensional arrays of light sensor modules distributed over large volumes of the transparent water in the deep Mediterranean Sea. The sensor modules register the time of arrival of the light and the brightness of the light to reconstruct the direction and energy of the neutrino. In order to achieve an accurate deployment of the mechanical structures and a precise reconstruction of neutrino induced events, the telescope includes an APS as mandatory sub-system that provides an accurate position of the mechanical structures in real time. Additionally, the APS could also be an excellent tool to study the feasibility of an acoustic neutrino detector and a possible correlation between acoustic and optical signals. The new detector KM3NeT is an excellent opportunity to continue with the study of the acoustic neutrino detection. The acoustic detection would allow the combination of the two neutrino detection techniques for a hybrid underwater neutrino telescope, especially considering that the optical based telescope needs acoustic sensors to monitor the position of the sensors. An Acoustic Beacon (AB) as part of the APS of KM3NeT has been developed in this thesis. Previously, the first emitter prototype was developed and it was installed in previous neutrino telescopes, such as ANTARES and NEMO, in order to be tested in situ. The analyses of the in situ test with the prototypes were performed as part of this thesis. The results obtained from the tests showed that the requirements for the positioning system are accomplished, just needing few improvements for the final version. The final version of the AB is composed by a piezo-ceramic transducer and an electronic board integrated in a single piece in a cylindrical hard-anodized aluminium vessel. The design and the work done for a precise laboratory test was performed achieving optimal results in all aspects As second main work performed in this thesis, a parametric transducer array able to mimic the acoustic signal generated by Ultra-High Energy (UHE) neutrino interaction in water was designed and developed. The first part was designing a single transducer able to emit parametrically the acoustic neutrino signal. Afterwards, the design of the complete array system composed of few units was performed in order to achieve a more energetic and directional bipolar pulse.