Major expansion of neutrino detector KM3NeT in the Mediterranean Sea successful

16 June 2022

In the Mediterranean, the installation of eleven new lines for the KM3NeT neutrino detector in the Italian sector has been completed. This immediately increased the size of the detector in the so-called ARCA sector by two and a half times. The first measurement data are expected soon.

KM3NeT is an extensive detector on the bottom of the Mediterranean Sea near Sardinia and near Toulon in France. Nikhef is part of the KM3NeT collaboration and closely involved in the construction of the detector and its components.


The detector consists of lines that reach up from the seabed, to which spheres with light sensors are attached. The signals from these sensors are used to reconstruct the tracks of passing neutrinos.

Such lines are coiled on a spool and lowered to the bottom of the sea from a lifting ship and uncoiled upward from there. An unmanned submarine then links them to the connection box on the bottom.

Two weeks

In a two-week sailing campaign, eleven new lines in the Italian ARCA sector were sunk and connected to a new connection box. The old connection box of the first eight lines was replaced, after which all eight lines now function. This brings the total number of lines to 19.

All lines appear to be functioning, says Nikhef PhD student Thijs Juan van Eeden, who assisted in the installation from KM3NeT’s coastal station in Sicily. “Currently, the commissioning is taking place: the tuning of the electrical and optical systems and eventually the data acquisition.”

This includes Jan Willem Schmelling and Antonio D’Amico, two Nikhef experts responsible for the design of the optical system. The first data are expected next week, he estimates.


Van Eeden worked shifts at the coastal station during the last week of the sea campaign to assist with communications between the ship and the control room. “A lot of waiting for what the team at sea is doing and then suddenly a lot of work with testing and checking. But super fun for a student like myself. For many physicists, the measurement data comes from a kind of black box. I have now seen up close what is involved before you have data.”

In time, KM3NeT should include hundreds of lines with thousands of sensor spheres, partly in Italy and partly in France, both at kilometers deep. With an observed water volume of one cubic kilometer of deep sea, the whole thing will then be the largest neutrino detector in the northern hemisphere, and a good complement to ICECUBE in the ice at the South Pole.

Ghost particles

The experiment looks both at the starry sky as a telescope, searching for sources of energetic neutrinos from the cosmos, and at the physical properties of the ghost particles themselves. Neutrinos have hardly any mass and are a relatively poorly studied part of the standard model, mainly because they can hardly be observed directly.