In December 2015, scientists and engineers started the installation of KM3NeT. Once completed, it will be the largest neutrino detector in the Northern Hemisphere. Located in the depths of the Mediterranean Sea, the telescope will be used to study the fundamental properties of neutrinos and map the high-energy cosmic neutrinos emanating from extreme cataclysmic events in the Universe.
On board the ship Ambrosius Tide, the first detector string – wound, like a ball of wool, around a spherical frame – arrived at the KM3NeT-It site south of Sicily. The detector was anchored to the seabed at a depth of 3500 m and connected to a junction box on the seafloor, using a remotely operated submersible controlled from the ship. The junction box is connected by a 100 km cable to the shore station located in Portopalo di Capo Passero in the south of Sicily.
Marco Circella, technical coordinator of KM3NeT, explains: “The large depth of sea water shields the telescope from particles created by cosmic rays in the atmosphere above the telescope. Constructing such a large infrastructure at these depths is a tremendous technical challenge. Making the underwater connections requires custom-designed electrical and fibre optic connectors. The crew of the Ambrosius Tide are experts in performing such delicate submarine operations.”
After verification of the quality of the power and fibre optic connections to the shore station, the go ahead was given to trigger the unfurling of the string to its full 700 m height. During this process, the deployment frame is released from its anchor and floats towards the surface while slowly rotating. In doing so, the string unwinds from the spherical frame, eventually leaving behind a vertical string with sensor modules. The string was then powered from the shore station and the first data from the sensor modules started streaming to shore and data taking has continued since.
The successful acquisition of data from the abyss with the novel technology developed by the KM3NeT Collaboration is a major milestone for the project. It represents the culmination of more than ten years of research and development by the institutes comprising the international collaboration.
Maarten de Jong, spokesperson of KM3NeT, said: “This important step in the verification of the design and the technology will allow the KM3NeT collaboration to proceed with confidence toward the installation of neutrino detectors at the sites in the Mediterranean Sea off-shore from Italy and France. A new era in neutrino astronomy has begun”.
Neutrinos are the most elusive of elementary particles and their detection requires instrumentation of enormous volumes: the KM3NeT neutrino telescope will occupy more than a cubic kilometre of seawater. It comprises a network of several hundred vertical detection strings, anchored to the seabed and kept taut by a submerged buoy. Each string hosts 18 light sensor modules equally spaced along its length. In the darkness of the abyss, the modules register the faint flashes of Cherenkov light that signal the interaction of neutrinos with the seawater surrounding the telescope.
The international KM3NeT Collaboration consists of 35 research groups from France, Germany, Greece, Italy, Morocco, The Netherlands, Poland and Spain.
More information on the KM3NeT can be found at: www.km3net.org