First building block KM3NeT detector ready
On 19 January the neutrino research at Nikhef reached an important milestone. After the successful anchoring of a prototype detector in May 2014, researchers and technicians have worked hard for the past six months to complete the first component for the KM3NeT detector (a 700 metre-long line with 18 glass spheres).
KM3NeT is the successor of ANTARES that was used to make initial studies of neutrinos (uncharged subatomic particles that interact very weakly with matter) originating from the cosmos with the help of a telescope located at the bottom of the Mediterranean Sea. However, the study of neutrino sources requires a telescope much bigger than ANTARES. A new project was therefore started with the aim of constructing a neutrino telescope several cubic kilometres in size: KM3NeT.
The building blocks of KM3NeT are Digital Optical Modules (DOMs). These are glass spheres filled with 31 photomultipliers that measure light in the deep sea caused by the electrically charged reaction products of neutrino interactions. To lay the lines on the seabed a new anchoring technique was devised in collaboration with NIOZ Royal Netherlands Institute for Sea Research on Texel. The entire line is first of all wrapped around a frame and then placed on the sea floor. By means of an acoustic signal the frame releases the line and it unrolls and comes to lie flat on the seabed.
Nikhef researcher Els Koffeman is the technical coordinator: "The detector is largely a Nikhef design; from the concept of the DOMs to the realisation. We have also made a substantial contribution to the electronics, optical network and software."
Ronald Bruijn, coordinator of the DOM production at Nikhef, says: "The first line that is now ready for transport was assembled at Nikhef. We are really proud that we have realised this within the timeframe set. This first line will be anchored near Marseille in the Spring. The construction of the other DOMs will soon take place not only at Nikhef but also at four other production lines in Europe that will be up and running soon."
Phase 1 of KM3NeT consists of 31 lines of 18 spheres; 24 in Italy and 7 in France. Aart Heijboer, KM3NeT programme leader at Nikhef, says: "The funding that has already been received, including contributions from Italy and France, is being used to construct the first part of the detector. These 31 lines are a first step. If everything goes according to plan we expect to be able to receive funding for the next step (phase 1.5). Then we will be able to start the scientific harvest. Ultimately with about 700 lines (phase 2) we will be able to realise our scientific ambitions."
What exactly will these spheres measure?
Nikhef researcher Maarten de Jong is the spokesperson for the international KM3NeT collaboration and explains what the spheres will measure: "Our primary goal is to measure cosmic neutrinos. By doing that we can learn a lot about the extreme energetic processes that take place in astrophysical objects. For example, we hope to be able to determine the origin of cosmic radiation, 100 years after its discovery. This astronomy aspect is very relevant, especially since the evidence found in 2013 by the IceCube Neutrino Observatory at the South Pole for the existence of such cosmic neutrinos. In addition the collaboration will focus on measuring the as yet unknown properties of neutrinos: the ranking of their intrinsic masses. The same technology can be used for this but then the glass spheres and the lines must be placed closer together. It is fantastic that the technology developed here at Nikhef can be used for both lines of research."
Why on the seafloor?
De Jong: "Neutrinos are infamous for the fact that they are very difficult to detect. Therefore the detector must be enormously heavy (and therefore enormously large): literally cubic kilometres. Of course that will not fit in a standard laboratory but it can fit in the sea. We are therefore building a giant but unmanned laboratory on the seafloor."