Following a successful four-day campaign at sea last week, five new lines of KM3NeT detector spheres have been successfully deployed on the deep-sea seabed off the coast of the French port of Toulon.
The ORCA section of the undersea neutrino telescope now comprises 38 lines, anchored at a depth of 2,400 metres. From the seabed, they extend 200 metres upwards, each containing 18 detector spheres (DOMs).
ORCA is a relatively small and compact array of neutrino detectors that primarily measures the properties of observed neutrinos. In addition, there is the larger Italian ARCA section of KM3NeT, with strings up to 700 metres long that, like a telescope, searches for sources of neutrinos in the starry sky.
In addition, a new acoustic beacon was installed last week for positioning, and a spare battery was replaced.
The operation was carried out from two vessels: the hoisting vessel Castor02 for lowering the lines, and the mother ship Janus II for an unmanned Apache submersible.
Neutrinos are elementary particles with virtually no mass, released during nuclear processes. They roam the universe in vast numbers, but interact very little and are therefore difficult to detect. Their properties are relatively poorly understood; for example, it is unclear how they acquire their tiny mass.
KM3NeT is a detector currently under construction that observes a cubic kilometre of completely dark deep-sea water. Incoming neutrinos can occasionally cause light traces within it, which are recorded by the network of sensors for analysis.
The signals from the neutrino telescope under construction are transmitted via cables to the coastal stations in Sicily and Toulon for physical studies. Nikhef is one of the designers and builders of KM3NeT and is closely involved in the scientific research using it.
KM3NeT is being gradually expanded and will eventually comprise approximately 115 (ORCA) and 230 (ARCA) lines. The measured signals have been studied ever since the first installations. In early 2025, KM3NeT reported the heaviest cosmic neutrino impact ever recorded, from an unknown source.
