The NEMO directional optical module: design and prototyping

NEMO (NEutrino Mediterranean Observatory) studies new technologies for the construction of a very large volume (Km3 - scale) underwater detector, devoted to astrophysic neutrino measurements, in the KM3NeT framework: this is a promising tool to better understand the mechanisms that originate the cosmic rays. Muon neutrinos can be detected by identifying and reconstructing the trajectory of the muon generated after the charged current interaction of the neutrino. The newly developed Directional Optical Module (DOM) will solve the ambiguity to identify the direction of the incoming Cherenkov photons. The DOM is based on the new development of a four anodes, 10 inches photomultiplier (PMT) from Hamamatsu Photonics. A light concentrator has been designed to exploit the directional capabilities of the PMT. The new high voltage, low power active bleeder needed to supply the dynodes chain will be presented. An interface to adapt the new device to the standard NEMO data acquisition system has been designed and tested in laboratory. Two complete DOMs will be integrated in the full NEMO tower which will be deployed in Summer 2008 for the NEMO Phase 2 activity in the selected site, at 3500 m depth, 40 miles South East from Capo Passero (Sicily, Italy) in the Mediterranean sea.