Cherenkov Water Detector (CWD) NEVOD

Experimental Complex (EC) NEVOD was created for scientific investigations in the priority areas of fundamental research and training of specialists in real conditions of modern physics experiment. The complex includes several unique physical detectors and setups that have no analogues in the world, as well as the system of test stands that are used as for scientific research so for training of students. EC NEVOD, which is the basis of the scientific and educational center of a new type, was organized and operates with the support of Ministry of Education and Science of the Russian Federation and Rosatom. Its creation was awarded with the prize of the President of the Russian Federation in the field of education in 1997. Creation of CWD NEVOD coincided with a turning point in the history of Russia: construction of the building of the experimental complex was completed in 1989. The first part of CWD was launched into operation in 1995. 

The basis of the experimental complex is the Cherenkov water detector of large volume (2000 m3). NEVOD is the world's first multifunctional water detector on the Earth's surface, designed to explore all the major components of cosmic rays, including the neutrino flux from the bottom hemisphere.

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 Experimental Complex NEVOD.


The detecting system of Cherenkov water detector is located in the water pool with internal dimensions 9x9x26 m3 and represents a spatial lattice, in which nodes the quasi-spherical modules (QSM) , registering the Cherenkov radiation from any direction with almost equal efficiency, are arranged. Structurally, the lattice is formed of vertical strings consisting of 3 or 4 modules. Water pool sizes are suitable for installation of up to 19 planes, 67 strings, 241 QSM. Since the experimental complex NEVOD is the first Cherenkov water detector at the Earth's surface and acts as a prototype for future large-scale setups, during its designing the possibility of using of various layouts and orientations of modules has been foreseen. Triggering system allows to select different classes of events by the number and location of triggered QSM.

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 Quasispherical measuring module: the appearance of QSM (left); scheme of QSM response quasi-sphericity (right).

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Detecting system of CWD NEVOD.

Data acquisition system allows to record all the necessary information for subsequent reconstruction of detected events. 

For the calibration of photomultipliers of modules during the long measurement series the system of calibration telescopes (SCT), which includes the upper scintillation counters located on the top of the water pool, and lower ones located at the bottom, is used. Any pair of upper and lower counters is a narrowly focused telescope that allows to calibrate quasi-spherical modules using Cherenkov radiation from the allocated muons with known tracks. Each counter is a sealed housing inside of which the scintillation plate with size 20x40x2 cm3, PMT, voltage divider and preamplifier are located. Light flashes generated by particles in the scintillator are collected by optical fibers to the photocathodes of photomultipliers FEU-85, which signal is amplified and sent to the external system of amplitude analysis and the formation of an autonomous and system trigger. SCT feature is the ability to analyze the amplitude of the recorded signals from the scintillation detectors. Therefore, two planes of detector, separated by a water layer of 9 m, is a good detector for registration of multiparticle events such as cores of EAS and muon bundles.

Experimentally, CWD NEVOD combines the functionality of the muon hodoscope with 4π-geometry providing event registration from any direction and Cherenkov water calorimeter for measuring the energy of the muon component of cosmic rays. To solve the first problem, at the Novosibirsk factory "EKRAN" in close cooperation with experts from Moscow Engineering Physics Institute the new photomultiplier FEU-200, which application allows to significantly reduce the noise of individual channels of the measuring system and triple the efficiency of detection of Cherenkov radiation from individual particles, have been developed. To solve the second problem, it was necessary to improve the detection of single muons from SCT (normalization point) and substantialy (≈ 100 times) expand the dynamic range of recorded signals using parallel signal pickup from one of the earlier dynodes. As a result of this work, a new recording system of measuring complex CWD NEVOD has been designed and created.

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Quasispherical modules of CWD NEVOD in water.