Abstract
KM3NeT is a future research infrastructure in the Mediterranean Sea housing the large Cherenkov telescope arrays of optical modules for neutrino detection. The detector control and data transmission system is based on fibre optical technology. For timing calibration of the detector signals the optical system is used to send and fan-out an onshore clock signal, derived from a GPS receiver, to all optical modules in the deep sea. The optical modules use this clock signal to time stamp the light pulses detected by the photomultipliers inside the modules. The delay time between the GPS clock on shore and the clock in each optical module is measured with sub-nanosecond precision using a White Rabbit based timing calibration system. The aspects of the optical system relevant for the timing calibration and the quantification of their effect will be presented.
Highlights
The final configuration of the arrays of optical modules of the KM3NeT neutrino telescope being installed at the bottom of the Mediterranean Sea will comprise a total instrumented volume of several cubic kilometres to detect Cherenkov light from traversing neutrino-induced leptons [1]
The delay time between the GPS clock on shore and the clock in each optical module is measured with sub-nanosecond precision using a White Rabbit based timing calibration system
Main electro-optical cables (MEOCs) connect the seabed infrastructures with the shore station at distances between 40 km (KM3NeT-Fr) and 100 km (KM3NeT-It)
Summary
The final configuration of the arrays of optical modules of the KM3NeT neutrino telescope being installed at the bottom of the Mediterranean Sea will comprise a total instrumented volume of several cubic kilometres to detect Cherenkov light from traversing neutrino-induced leptons [1]. During the first construction phase 31 detection units (DU) will be installed configured as long vertical lines each containing 18 Digital Optical Modules (DOM) and each DOM containing 31 photomultipliers [2]. These DUs will be deployed at two locations in the Mediterranean at depth of 2500 m (KM3NeT-Fr) and 3500 m (KM3NeT-It) and connected to seabed networks of electro-optical cables and junction boxes. The KM3NeT timing calibration depends on the measurement of the delay between the system clock on shore and all the DU-base modules and DOMs. After an introduction on the principle. The effects of pressure and temperature on the propagation delays over the optical fibres in the VEOC of a DU (Fig. 1) are described in Sects. 4 and 5
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