HREPHAH 0H3HKA, 2004, moM 67, № 11, c. 2075-2078
RARE PROCESSES AND ASTROPHYSICS
NESTOR EXPERIMENT IN 2003
©2004 V. A. Zhukov1)*. A.Aloupis2>, E. G. Anassontzis2), N. Arvanitis3), A. Babalis3), A. Ball4\ L. B. Bezrukov1), G. Bourlis5), A. V. Butkevich1), W. Chinowsky6), P. E. Christopoulos7), A. Darsaklis3), L. G. Dedenko1^ D. Elstrup8), E. Fahrun8), J. Gialas9), Ch. Goudis7), G. Grammatikakis9), C. Green8), P. K. F. Grieder10), S. K. Karaevsky1), P. Katrivanos11), U. Keussen8), J. Kiskiras3), Th. Knutz8), D. Korostylev12), K. Komlev13), J. Kontakxis2), P. Koske8), J. G. Learned14), V. V. Ledenev13), A. Leisos5), G. Limberopoulos3), J. Ludvig6), J. Makris12), A. Manousakis-Katsikakis2), E. Markopoulos3), S. Matsuno14), J. Mielke8), Th. Mihos3), P. Minkowski10), A. A. Mironovich1), R. Mitiguy14), S. Nounos2), D. R. Nygren6), K. Papageorgiou3), M. Passera10), C. Politis7), P. Preve2), G. T. Prybylsky6), J. Rathley8), L. K. Resvanis2),3), M. Rosen14), N. Schmidt8), Th. Schmidt8), I. Siotis15), A. E. Shnyrev1), J. Sopher6), T. Staveris3), G. Stavrakakis16), R. Stokstad6), N. M. Surin1), V. Tsagli3), A. Tsirigotis3), J. Tsirmpas3), S. Tzamarias5), O. Vasiliev12), O.Vaskin13), W. Voigt8), A. Vougioukas3), G. Voulgaris2), L. M. Zakharov1), N. Ziabko12)
(The NESTOR Collaboration) Received January 20, 2004
NESTOR is a submarine high-energy muon and neutrino telescope, now under construction for deployment in the Mediterranean close to Greek shores. The first floor of the NESTOR with 12 optical modules had been deployed successfully in March 2003 together with electronics system. All systems and the associated environmental monitoring units are operating properly and data are being recorded. The status of the NESTOR project is presented. We outline briefly the construction of deepwater neutrino telescope, properties of the NESTOR site, infrastructure of the project, the deployment of the first floor and its current operation. First data are presented and plans for next steps are summarized.
^Institute for Nuclear Research, Russian Academy of Sciences, Moscow.
2)Physics Department University of Athens, Greece.
3)NESTOR Institute for Deep S ea Research, Technology and Neutrino Astroparticle Physics, Pylos, Greece.
4)CERN, Geneva, Switzerland.
5)School of Science and Technology, Hellenic Open University, Greece.
6)Lawrence Berkeley National Laboratory, CA, USA.
7)Physics and Astronomy Department University of Patras, Greece.
8)Centerfor Applied Marine Science Research and Technology Westcoast (FTZ), Buesum, University of Kiel, Germany
9)Physics Department University of Crete, Greece.
10)Institute of Physics University of Bern, Switzerland.
11)Institute of Informatics and Telecommunications NCSR DEMOKRITOS, Greece.
12)Institute for Geophysics University of Hamburg, Germany.
13)Experimental Design Bureau of Oceanological Engineering, Russian Academy of Sciences, Moscow.
14)Department of Physics and Astronomy University of Hawaii at Manoa, Honolulu, HI, USA.
15)National S cience Foundation, Greece.
16)Institute for Geodynamics Athens Observatory, Greece.
1. THE NESTOR TOWER
The NESTOR (Neutrino Extended Submarine Telescope with Oceanographic Research) will consist of a tower (Fig. 1) with 12 rigid hexagonal floors of 32 m in diameter and vertically spaced at 30 m [1—4]. Six arms attached to the central frame are built from titanium tubes to form a light-weight and rigid lattice girder structure. Three girders of 5 m length of each are connected one to other and to the central frame with hinges. This made the construction collapsible and very convenient for transportation and deployment. In water folded arms open automatically or with help of divers. All ends of arms are coupled round of floor by ropes for stability.
The 1-m diameter titanium sphere that houses the floor electronics is mounted at the central support frame. Two optical modules (OM) are installed at the end of each of the six arms, one facing upwards and the other downwards. The OMs are also installed above and below the central titanium sphere making
E-mail: vlzhukov@mail.ru
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NESTOR tower
Buoys -0 168 PMTs (facing up & down)
32 m diameter 30 m between floors
3800 m
12 floors
Electro-optical cable 30 km to shore station
Anchor
Fig. 1. The NESTOR tower.
atotal 14 per floor. A full NESTOR tower will consist of 168 OMs.
The NESTOR optical module consists of 15-in. HAMAMATSU photomultiplier (PMT) R2018-03 surrounded with ^-metal cage inside 17-in. glass pressure housing (the BENTHOS sphere) [4]. A PMT is fixed inside a glass sphere by silicone gel gasket. Glycerin is used for optical coupling. Inside the glass spheres the 24/2500 V D.C. converter and pressure gauge are mounted. OM is connected to the central titanium sphere by hybrid electrical cable with 7 pins deepwater connectors at the both ends. Cables have coaxial and twisted pairs for PMT signal and power (24 V D.C.) transmission and H.V. control and monitoring.
Small LED modules will be installed between floors for OMs calibration. The gain and the timing characteristics of the OMs will be monitored continuously by LED placed halfway between floors.
The tower is connected to the sea bottom unit, which contains the anchor and its release mechanism, the junction box for the electro-optical cable coming from shore and a number of environmental monitoring units.
Connections of the shore cable to the junction box and internal cables from the junction box to each titanium sphere, from titanium sphere to the OMs, are all made at the surface during deployment. This
avoids the use of deep submersible vehicles and wet-mating connections.
Eventually a number of such towers could be deployed to form a very large neutrino telescope.
2. THE NESTOR SITE The NESTOR tower will be deployed in the deepest part of the Mediterranean, very close to the southwestern coast of the Peloponnese. The deployment site is an under water plateau 65 km2 in area at an average depth 3800 m which is a constant to within ±50 m over its entire area. The center of the plateau with coordinate 36°37.5'N and 21°34.6/E is approximately 20 km off the shore. Therefore, the detector, deployed at this site, can be connected to shore by modest length of cable.
Far from the effluents of major rivers, NESTOR site benefits from extremely clear water with a trans-missivity of 55 ± 10 m at 460-nm wavelength, weak water current consistently below 10 cm/s, and water temperature 14°C [2]. The mean density of sea floor sediments is near 1.5 g/cm3 which indicates a slow accumulation rate of 7—18 cm over 10 000 yr.
The optical background due to 40K and bioluminescence was measured to be 75 kHz per OM at the 0.25 p.e. level. The bioluminescence bursts indicate duration not longer than 15 s (3—5 s typically) and frequency of about 20 per hour.
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NESTOR EXPERIMENT IN 2003
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3. THE NESTOR INFRASTRUCTURE
The NESTOR neutrino telescope is a part of the scientific program of the NESTOR Institute, in the town of Pylos on the bay of Navarino. It has very convenient location: 280 km from Athens, 40 km from Kalamata International Airport, 45 km from the Industrial and Port city of Kalamata. The NESTOR site is 15 nautical miles from Pylos.
The NESTOR infrastructure is well developed now. The Institute building (1000 m2) houses fully equipped electronics laboratory (analog and digital), offices, conference room, library, small workshop. There is a cluster of 36 dual Pentium III-based computers, 500 MHz, with 36 G flops, 4 G RAM, 416 G HD. Second building consists of machine shop, equipped with turning, milling, drilling, cutting, welding, and other machines. The optical laboratory, equipped with all necessary stands for PMTs, OMs and electronics system tests, storage room, large and small hyperbaric chambers are installed in the second building.
A 30-km-long deep sea cable with 18 mono mode optical fibers is laid from the shore to the deep-sea site. One copper conductor can deliver up to 6 kW of D.C. power. Power return is done electrolytically via the sea. The scientific payloads are attached at the end of the cable. The sea end of cable is liftable in order to change the deepwater equipment. The cable landing is terminated in the Terminal cable station in the village of Methoni (11 km from Pylos).
The NESTOR has a test facility created at 50 m depth in the Navarino Bay, near the Sfakteria island. It can be used almost all year around. The 4.5-km-long deep sea cable with 12 mono-mode fibers and one copper conductor joins the Institute building with junction box located on the sea end. The goal is that the deep sea instruments should be tested for long time in the bay before they are deployed in the depth.
The NESTOR owns a little fleet: a score of less than 5-m-long boats plus a 12.5-m open-sea fast cruiser, and a 6.2-m open-sea fast rigid hull inflatable boat. The cable laying vessel THALES of Hellenic Telecommunication Organization, is available to NESTOR, free of charge, for various tests. Moreover, the Pylos harbor has a host of medium size vessels with cranes and one large tugboat as well.
4. DEPLOYMENT OF THE FIRST DETECTOR FLOOR
The electro-optical cable from the shore station to the NESTOR site was laid in 2000. In January 2002 the end of the cable was brought to the surface by recovery rope and connected to the junction box on the telescope bottom unit or "pyramid". The
Data collected with 4-fold coincidence trigger (in Hz)
Thresholds at 30 mV Thresholds at 120 mV
Measured total trigger rates (>4 fold) 2.61 ±0.02 0.12 ± 0.01
MC prediction (atmospheric muons only) 0.141 ±0.005 0.12 + 0.01
pyramid also houses the power return electrode, the anchor with its release mechanism and environmental monitors. Bad weather made it dangerous to attach a floor detector on that occasion. However, useful data were transmitted to the shore from the pyramid and long
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