- Email: [email protected]
Status of NESTOR, a deep sea neutrino telescope in the Mediterranean
ELSEVIER
Nuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
PROCEEDINGS SUPPLEMENTS
Status of NESTOR, a deep Sea Neutrino Telescope in the Mediterranean E. G. Anassontzis #, M. Barone #, E. Fahrun #, C. Foudas #, G. Gialas #, G. Grammatikakis #, S. Katsanevas #, C. Kourkoumelis #, A. Manousakis-Katsikakis #, A. Odian #, L. K. Resvanis # , I. Siotis # , S. A. Sotiriou # , G. Voulgaris #, A. E. Ball £" , A. M. Cartacci &, L. Dell'Agnello&, B. Monteleoni ~ , V. A. Naumov ~", L. Perrone ~, A. Martini S, G. Nicoletti $ , L. Trasatti $, V. Valente $, U. Keusen 8, P. Koske ~, J. Rathlev ~, G. Voigt ~, F. Curti$, G. De Marchist, L. Piccari t, F. Ameli§, M. Bonori§, C. Bosio§, S. Bottai§, A. Capone §, P. Desiati§, F. Massa§, V. Rikalin§, E. Valente§, L. B. Bezrukov ~, A. V. Butkevich 1, L. G. Dedenko ¶ , S. K. Karaevsky I, A. Mironovich I, L. M. Zakharov ¶, I. M. Zheleznykh¶ , V. A. Zhukov I, T. A. Demidova~, A. Deyneko ~, A. P. Eremeev ~, V. T. Paka ~, A. A. Permyakov ~, M. N. Platonov ~, V. K. Rucol ~, N. M. Surin ~, N. A. Sheremet ~, V. I. Albul?, and V. V. Ledenev t
# University of Athens, University of Crete, Demokritos NRC, Greece £ CERN, Geneva, Switzerland INFN Firenze and Department of Physics, Firenze, Italy $ INFN Laboratori Nazionali di Fraseati, Frascati, Italy fl University of Kiel, Kiel, Germany § INFN Rome and Department of Physic of Univeristy "La Sapienza", Rome, Italy Fondazione U.Bordoni, Rome, Italy ¶ Institute ]or Nuclear Research, R. A. S., Moskow, Russia ¢ Institute of Oceanology, R. A. S., Moskow, Russia t Experimental Design Bureau of Oceanological Equipment, R. A. S., Moskow, Russia In the last few years a great interest has been expressed for the construction of a Neutrino Astroparticle Physics Laboratory in the Mediterranean. The NESTOR collaboration made important progresses and plans soon to deploy in deep sea a detector with .~ 104 m s effective s~b~face. This detector will be able not only to demonstrate the validity of the experimental approach but also to start da~;a collection and then real Neutrino Astrophysics. The status of the preparation of the experiment and the future programs are described.
1. I N T R O D U C T I O N The NESTOR project is described in detail in the proceedings of two workshops [1,2] held in Pylos in 1992 and 1993 and in more recent papers [3,4] contributed to Conferences. It consists in a matrix of phototubes, placed in deep sea, to detect the Cerenkov radiation produced by muons in a large volume of sea water. The detector is designed mainly to search for astrophysical sources of high energy neutrinos and it is rather compact and isotropic. For these reasons it will be also a good instrument to study atmospheric neutrino fluxes or to search for neutrinos from other sources like supernovae explosions or *Partecipation mainly for long base-line neutrino beam studies 0920-5632/98/$19.00 © 1998 ElsevierScienceB.V. All rightsreserved. PII S0920-5632(98)00047-4
neutralino annichilations. The selected site is in Greece, in the Ionian Sea, close to the town of Pylos and can accommodate a detector with a sensitive area larger than 106 m 2 at a depth greater then 3.8 km. The detector will be modular. The basic active element is a hemispherical (15" diameter) photomultiplier tube (PMT) made by HAMAMATSU. 14 PMTs are grouped in a planar mechanical structure (floor) with hexagonal shape. Each two P M T will be placed back-toback and located at the centre and at the vertices of the hexagon. The hexagonal structure is made by six arms, each 16 m long. Twelve floors will be then grouped vertically, at a distance of 20 m, to form a Tower. The Tower (fig. 1) will be deployed in a single operation, it will contain 168
248
E.G. Anassontzis et aL /Nuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
PMT (84 looking up, 84 looking down), it will include a volume of ,~ 200 K t o n s of water and its sensitive area for TeV muons will be ,~ 104 m 2.
Seo -Su~fcce
16m 20-30
m
2 0 0 - 5 0 0 Kton= conto;ned votume
• och floor ;s eloctHcolly o¢~d electr~ically T~dependent
NOT TO SCALE
-
~o-Bottom
), electro-opt;col cable (12 f;bres, l ~;ber/floor) to shore --~ 7,5 m;les
Figure 1. A NESTOR tower
2. T h e N E S T O R Site The site selected by NESTOR Collaboration is in Greece, at the S.W. of Peloponnesos, in the depths (3800 m) of the Ionian Sea, is close to Pylos and is 11 nautical miles away from the small town of Methoni. In that location, which coordinates are 36°37.5'N, 21°34.6'E, NESTOR Collaboration has identified a large plateau (,-8 x 9 k m 2) where the depth is constant to within +50m, and that fulfils the specific environmental requirements which are desirable for the operation of a deep underwater neutrino detector [5]. Several results obtained with extensive studies of the water properties have been already reported: • transmissivity measurements showed that the water transmission length is 55:1: 10m at A = 46Ohm [6,7]; • underwater currents have been measured over five years and have been found to be less than 10cm/sec [8]
• a sedimentology of the sea bottom has shown a nice firm clay, free of sediments and good for anchoring [9]. New studies have been carried out in the last two years. In the summer of 1996 a set-up based on two Optical Modules (OM) was deployed in NESTOR site. During this operation the single rate of the two PMTs has been measured, for several thresholds ranging from one quarter of a photoelectron (p.e.) to 5 p.e.. The contribution to the single rate due the 4°K beta decay has been measured by comparing the measured single rates with the corresponding ones measured in laboratory. The results indicates that the 4°K contribution to the single rate amounts to ,~ 55 k H z for one quarter of p.e. threshold and reduces by an order of magnitude for 2 p.e. threshold. During the same operation we also observed some intermittent burst of signals, in both PMTs, of durations 3-5 seconds, occurring in less than 1% of the experimental time, that we attributed to bioluminescent activity. A more quantitative analysis of this effect is needed. An other important result achieved by the group is the detailed study of the sea bottom and of the access to the shore for the electro-optical cable needed for power and data t~nsmission. 3. C o n s t r u c t i o n and Tests O f D e t e c t o r Elements
3.1. M e c h a n i c s NESTOR Collaboration made important progresses in the definition of detector elements and has started the construction of them. About 40 Optical Modules have been at present completed. An Optical Module consists, basically, in a phototube housed in a glass sphere able to protect it from the hydrostatic pressure when positioned in the deep sea (~, 400 atm). All the OM have been successfully tested in a pressure chamber at ,,~ 500 atm. The group has constructed the mechanical structure for four floors: two floors are made by Aluminium and two floor by Titanium. For both versions the arms are 16m long. In the floors made by Aluminium the arms are rigid, in the Ti floors each arm is foldable and made by 3 equal length sectors. Both structures float in sea
E.G. Anassontzis et aL /Nuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
249
NESTOR On-shore/off-shore optical link "---1
DFB laser (15SOnm)
e T ~ n ~ I coilx-
(1550 nm)
~.
To TX 1530 nm
\
Vl--/I DFB laser (1530 nm )
optical coupler
-3 dB ~
1530/1550 -1 dB 7
for 30 Kmdispersion sh~ed fiber atl SOOnm
coax. From H ~ TXin adjacent plane
j ~
~ _ [ se~m~ty ~ -~4 oum
[ ] J [
"
. ,___L, . (1530 nm) sensitivity
-24 dBm
DFB laser (1310 nrn )
Figure 2. The optical link water when equipped with the Optical Modules and with the central lm diameter Ti sphere. The central Ti sphere is used to hold the electronics for data collection and transmission. The group has tried the deployment operation of both type of floor structure in the bay of Navarino, a well protected bay in front of the Pylos town. Both operations have been done there several times, in shallow water, since the autumn of 1996 and allowed to gain experience on the deployment technique. As a result of these tests we concluded that, in agreement with expectations, a proper manipulation of the two floor structures during deployment produce stresses well below the breakdown limit. Special tests have been done with the two Aluminium floors: in the Navarino bay, during 1996 fall, and then, during Spring 1997, also in deep water in the NESTOR site. The two floors have been deployed, while by means of an anchor and ropes they where kept at a vertical distance of 20 m, and recovered. In the NESTOR site they have been put down to a depth of ,-~ 2500 m. These tests gave us confidence in the operational method and allowed us to learn experience for the 12 floors Tower deployment.
3.2. O p t i c a l Link The transmission of the signal over 30 km forces the choice of a single mode (or monomode) optical fibre attd of a laser as light source. Power transfer to'the NESTOR tower and data retrieval to the shore will then be performed with a standard deep sea electro-optical cable. This is composed of (at least) 12 monomode optical fibres, one for each floor. We have designed and constructed the electronics to drive the transmitting laser and the receiving diode. Both cards have been used, over 3 0 k m of monomode fibre, and allow, at 1 Gb/s rate, a transmission with a Bit Error Rate less than 10 -13 , fully in agreement with the need of the experiment. Redundancy and independence among floors are the fundamental requirements for the data transmission to get high Mean Time To Failure. Each floor of one tower is provided with two lasers working at about 1550nm (1535nm and 1555nm) and a receiver, working at about 130Ohm, coupled to one optical fibre (fig. 2) . The data produced by each floor are transmitted, at the same time, by two lasers: the laser (1555nm) coupled to the fibre connected to the floor and the laser (1535nm) coupled to the
250
E.G Anassontzis et aL INuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
fibre connected to an adjacent floor. In this way we gain then a factor of two in safety and in the redundancy of the transmitted data. 3.3. Electronics The electronics that we have developed [10] and constructed to acquire the PMT pulses is able to transmit to the shore laboratory, in real time, the complete pulse of each PMT signal, maintaining the time coherence between PMTs. This electronics allows: 1) the knowledge of the pulse shape of each PMT (each PMT is served by a Flash ADC) 2) a real time control of the behaviour of each single PMT (for each PMT it is possible, from the shore, to control the HV and to vary the pulse threshold level) 3) to decide the trigger logic on shore, having so the maximum flexibility.
SO
Co~ant ~ean
70 60
/~
40
~
9.072 / 6 64.72 ~03,8 166.__~1 O.
!
30 2O
102
~02.5
103
103.5
104
10~..5 105 105.5 MEASURED DELAv (ns) {r'/nd' 11.08 / 8 Co~*stant 63.58 Vean 217.8
70 60
S:gmo
0.1832
50 4C 30 20 10 0
216
Ill'l'
, I . z
216.5
217
i .... 217.5
i , i~,
218
; .... i .... I 218.5 219 2~9.5 MEASURED DELAY (ns)
Figure 3. Measured time difference for the same pulse sent, with fixed delays, in two different daughter cards. The distribution on top refers to a fixed delay of ,-~ lOOns, the bottom one to a delay of ,~ 200ns
Each Optical Module will be served by a single card (called daughter card), the 14 daughter cards
of each plane are placed on a mother board and the whole is located in the Ti sphere at the center of each floor. In the mother board the asynchronous information coming from the PMT's are organised and synchronously transmitted on the fibre. Several daughter cards have been produced and successfully tested. According to the specifications they have a dynamic range greater then 1000 (the range selected is from one quarter of p.e. to 400 p.e.), they allow an average PMT single rate bigger than 1 5 0 k H z and to sample the PMT pulse each 5ns. Two mother card have been produced and successfully tested. Each mother board allows the multiplexing (in time) of the 14 PMTs data and the transmission of a serial flux of data at 400Mb/s. To qualify our electronics we measured the resolution in the measurement of the time difference for pulses recorded by different daughter cards. With the 5 n s samplings we reconstruct the PMT pulse shapes then we estimate, for each pulse, the threshold crossing time. We found that the resolution in time is well below l n s and independent from the time delay (fig. 3). The on-shore receiving electronics consists in the optical receiver card, one card (called MEZZANINE) that transforms the 400Mb/s serial link irrto a 10Mword/s (40 bit words) flux of data and that is mounted on a commercial PAMETTE card (DIGITAL). The PAMETTE card, mounted on a PCI bus, is used to provide the zero suppression, the extraction of the time and pulse information of each PMT, then it allows the trigger formation. Each mother board transmits also the information of the Slow Control Sensors that will be located close to the floor to which they belong. The signals of these sensors are first acquired and conditioned by a Slow Control System [11] that has been designed by the Collaboration. A Slow Control unit is based on a microcontroUer equipped with external R O M and R A M , plus an additional boards, developed by the Collaboration, containing the interface with the pulses. A prototype card has been successfullytested and used in real tests.
E.G. Anassontzis et al./Nuclear PhysicsB (Proc. Suppl.) 66 (1998) 247-251 4. Conclusions During the past two years NESTOR Collaboration made great progresses. The Construction of Optical Modules is a well established and successful operation: more than 40 OM have been already constructed and tested. The mechanical structure for three floors has also been constructed and tested. A deployment operation of a two floor structure has been carried on in shallow (~ 40m depth) and in deep water (~ 2500m depth). The electronics for data acquisition (for PMTs and for Slow Control Sensors) and for the transmission on optical fibres has been finalised. Tests made on first prototypes have been fully satisfactory. Cards needed for the first two floors are under construction. We plan to be soon operational. REFERENCES 1. Proceedings of the 2na NESTOR International Workshop, ed. L.K. Resvanis (University of Athens,1992) 2. Proceedings of the 3rd NESTOR International Workshop, ed. L.K. Resvanis (University of Athens,1993) 3. A. Capone et al. In Proceedings of the 2~th International Cosmic Ray Conference , Rome, Italy, (1995) 4. S. Bottal et al. In Proceedings of the 24th International Cosmic Ray Conference , Rome, Italy, 1 (1995) 1080 5. L.K.Resvanis et al.: NESTOR, A Neutrino Particle Astrophysics Underwater Laboratory for the Mediterranean, High Energy Neutrino Astrophysics Workshop, Hawaii, March 1992, V.J.Stenger, J.G.Learned, S.Pakvasa and X.Tata editors, World Scientific (1992), p. 325. 6. S.A. Khanaev and A.F. Kuleshov, in: Proceedings of the 2nd NESTOR International Workshop, Fortress of Niokastro, Pylos, Greece, 19-21 October, 1992, edited by L. K. Resvanis (Physics Laboratory, University of Athens, Athens, 1993), p. 253. 7. E. Anassontzis et al., NucL Instruments and Methods A 349 (1994) 242.
25!
8. T.A. Demidova and I. A. Repin, in: Proceedings of the 2nd NESTOR International Workshop, Fortress of Niokastro, Pylos, Greece, 19-21 October, 1992, edited by L. K. Resvanis (Physics Laboratory, University of Athens, Athens, 1993), p. 284. 9. E. Trimonis and M. Rudenko, in: Proceedings of the 2nd NESTOR International Workshop, Fortress of Niokastro, Pylos, Greece, 19-21 October, 1992, edited by L. K. Resvanis (Physics Laboratory, University of Athens, Athens, 1993), p. 321. 10. M. Bonori et al. In NESTOR data transmission, Dipartimento di Fisica, Universita di Roma "La Sapienza", Nota Interna n. 1055, 25 maggio 1995 (1995) 11. P. Locchi, A. Martini and L. Trasatti, in First Test of CRONOS, the NESTOR Slow Control System, LNF-97/004 (IR), (1997)
Nuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
PROCEEDINGS SUPPLEMENTS
Status of NESTOR, a deep Sea Neutrino Telescope in the Mediterranean E. G. Anassontzis #, M. Barone #, E. Fahrun #, C. Foudas #, G. Gialas #, G. Grammatikakis #, S. Katsanevas #, C. Kourkoumelis #, A. Manousakis-Katsikakis #, A. Odian #, L. K. Resvanis # , I. Siotis # , S. A. Sotiriou # , G. Voulgaris #, A. E. Ball £" , A. M. Cartacci &, L. Dell'Agnello&, B. Monteleoni ~ , V. A. Naumov ~", L. Perrone ~, A. Martini S, G. Nicoletti $ , L. Trasatti $, V. Valente $, U. Keusen 8, P. Koske ~, J. Rathlev ~, G. Voigt ~, F. Curti$, G. De Marchist, L. Piccari t, F. Ameli§, M. Bonori§, C. Bosio§, S. Bottai§, A. Capone §, P. Desiati§, F. Massa§, V. Rikalin§, E. Valente§, L. B. Bezrukov ~, A. V. Butkevich 1, L. G. Dedenko ¶ , S. K. Karaevsky I, A. Mironovich I, L. M. Zakharov ¶, I. M. Zheleznykh¶ , V. A. Zhukov I, T. A. Demidova~, A. Deyneko ~, A. P. Eremeev ~, V. T. Paka ~, A. A. Permyakov ~, M. N. Platonov ~, V. K. Rucol ~, N. M. Surin ~, N. A. Sheremet ~, V. I. Albul?, and V. V. Ledenev t
# University of Athens, University of Crete, Demokritos NRC, Greece £ CERN, Geneva, Switzerland INFN Firenze and Department of Physics, Firenze, Italy $ INFN Laboratori Nazionali di Fraseati, Frascati, Italy fl University of Kiel, Kiel, Germany § INFN Rome and Department of Physic of Univeristy "La Sapienza", Rome, Italy Fondazione U.Bordoni, Rome, Italy ¶ Institute ]or Nuclear Research, R. A. S., Moskow, Russia ¢ Institute of Oceanology, R. A. S., Moskow, Russia t Experimental Design Bureau of Oceanological Equipment, R. A. S., Moskow, Russia In the last few years a great interest has been expressed for the construction of a Neutrino Astroparticle Physics Laboratory in the Mediterranean. The NESTOR collaboration made important progresses and plans soon to deploy in deep sea a detector with .~ 104 m s effective s~b~face. This detector will be able not only to demonstrate the validity of the experimental approach but also to start da~;a collection and then real Neutrino Astrophysics. The status of the preparation of the experiment and the future programs are described.
1. I N T R O D U C T I O N The NESTOR project is described in detail in the proceedings of two workshops [1,2] held in Pylos in 1992 and 1993 and in more recent papers [3,4] contributed to Conferences. It consists in a matrix of phototubes, placed in deep sea, to detect the Cerenkov radiation produced by muons in a large volume of sea water. The detector is designed mainly to search for astrophysical sources of high energy neutrinos and it is rather compact and isotropic. For these reasons it will be also a good instrument to study atmospheric neutrino fluxes or to search for neutrinos from other sources like supernovae explosions or *Partecipation mainly for long base-line neutrino beam studies 0920-5632/98/$19.00 © 1998 ElsevierScienceB.V. All rightsreserved. PII S0920-5632(98)00047-4
neutralino annichilations. The selected site is in Greece, in the Ionian Sea, close to the town of Pylos and can accommodate a detector with a sensitive area larger than 106 m 2 at a depth greater then 3.8 km. The detector will be modular. The basic active element is a hemispherical (15" diameter) photomultiplier tube (PMT) made by HAMAMATSU. 14 PMTs are grouped in a planar mechanical structure (floor) with hexagonal shape. Each two P M T will be placed back-toback and located at the centre and at the vertices of the hexagon. The hexagonal structure is made by six arms, each 16 m long. Twelve floors will be then grouped vertically, at a distance of 20 m, to form a Tower. The Tower (fig. 1) will be deployed in a single operation, it will contain 168
248
E.G. Anassontzis et aL /Nuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
PMT (84 looking up, 84 looking down), it will include a volume of ,~ 200 K t o n s of water and its sensitive area for TeV muons will be ,~ 104 m 2.
Seo -Su~fcce
16m 20-30
m
2 0 0 - 5 0 0 Kton= conto;ned votume
• och floor ;s eloctHcolly o¢~d electr~ically T~dependent
NOT TO SCALE
-
~o-Bottom
), electro-opt;col cable (12 f;bres, l ~;ber/floor) to shore --~ 7,5 m;les
Figure 1. A NESTOR tower
2. T h e N E S T O R Site The site selected by NESTOR Collaboration is in Greece, at the S.W. of Peloponnesos, in the depths (3800 m) of the Ionian Sea, is close to Pylos and is 11 nautical miles away from the small town of Methoni. In that location, which coordinates are 36°37.5'N, 21°34.6'E, NESTOR Collaboration has identified a large plateau (,-8 x 9 k m 2) where the depth is constant to within +50m, and that fulfils the specific environmental requirements which are desirable for the operation of a deep underwater neutrino detector [5]. Several results obtained with extensive studies of the water properties have been already reported: • transmissivity measurements showed that the water transmission length is 55:1: 10m at A = 46Ohm [6,7]; • underwater currents have been measured over five years and have been found to be less than 10cm/sec [8]
• a sedimentology of the sea bottom has shown a nice firm clay, free of sediments and good for anchoring [9]. New studies have been carried out in the last two years. In the summer of 1996 a set-up based on two Optical Modules (OM) was deployed in NESTOR site. During this operation the single rate of the two PMTs has been measured, for several thresholds ranging from one quarter of a photoelectron (p.e.) to 5 p.e.. The contribution to the single rate due the 4°K beta decay has been measured by comparing the measured single rates with the corresponding ones measured in laboratory. The results indicates that the 4°K contribution to the single rate amounts to ,~ 55 k H z for one quarter of p.e. threshold and reduces by an order of magnitude for 2 p.e. threshold. During the same operation we also observed some intermittent burst of signals, in both PMTs, of durations 3-5 seconds, occurring in less than 1% of the experimental time, that we attributed to bioluminescent activity. A more quantitative analysis of this effect is needed. An other important result achieved by the group is the detailed study of the sea bottom and of the access to the shore for the electro-optical cable needed for power and data t~nsmission. 3. C o n s t r u c t i o n and Tests O f D e t e c t o r Elements
3.1. M e c h a n i c s NESTOR Collaboration made important progresses in the definition of detector elements and has started the construction of them. About 40 Optical Modules have been at present completed. An Optical Module consists, basically, in a phototube housed in a glass sphere able to protect it from the hydrostatic pressure when positioned in the deep sea (~, 400 atm). All the OM have been successfully tested in a pressure chamber at ,,~ 500 atm. The group has constructed the mechanical structure for four floors: two floors are made by Aluminium and two floor by Titanium. For both versions the arms are 16m long. In the floors made by Aluminium the arms are rigid, in the Ti floors each arm is foldable and made by 3 equal length sectors. Both structures float in sea
E.G. Anassontzis et aL /Nuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
249
NESTOR On-shore/off-shore optical link "---1
DFB laser (15SOnm)
e T ~ n ~ I coilx-
(1550 nm)
~.
To TX 1530 nm
\
Vl--/I DFB laser (1530 nm )
optical coupler
-3 dB ~
1530/1550 -1 dB 7
for 30 Kmdispersion sh~ed fiber atl SOOnm
coax. From H ~ TXin adjacent plane
j ~
~ _ [ se~m~ty ~ -~4 oum
[ ] J [
"
. ,___L, . (1530 nm) sensitivity
-24 dBm
DFB laser (1310 nrn )
Figure 2. The optical link water when equipped with the Optical Modules and with the central lm diameter Ti sphere. The central Ti sphere is used to hold the electronics for data collection and transmission. The group has tried the deployment operation of both type of floor structure in the bay of Navarino, a well protected bay in front of the Pylos town. Both operations have been done there several times, in shallow water, since the autumn of 1996 and allowed to gain experience on the deployment technique. As a result of these tests we concluded that, in agreement with expectations, a proper manipulation of the two floor structures during deployment produce stresses well below the breakdown limit. Special tests have been done with the two Aluminium floors: in the Navarino bay, during 1996 fall, and then, during Spring 1997, also in deep water in the NESTOR site. The two floors have been deployed, while by means of an anchor and ropes they where kept at a vertical distance of 20 m, and recovered. In the NESTOR site they have been put down to a depth of ,-~ 2500 m. These tests gave us confidence in the operational method and allowed us to learn experience for the 12 floors Tower deployment.
3.2. O p t i c a l Link The transmission of the signal over 30 km forces the choice of a single mode (or monomode) optical fibre attd of a laser as light source. Power transfer to'the NESTOR tower and data retrieval to the shore will then be performed with a standard deep sea electro-optical cable. This is composed of (at least) 12 monomode optical fibres, one for each floor. We have designed and constructed the electronics to drive the transmitting laser and the receiving diode. Both cards have been used, over 3 0 k m of monomode fibre, and allow, at 1 Gb/s rate, a transmission with a Bit Error Rate less than 10 -13 , fully in agreement with the need of the experiment. Redundancy and independence among floors are the fundamental requirements for the data transmission to get high Mean Time To Failure. Each floor of one tower is provided with two lasers working at about 1550nm (1535nm and 1555nm) and a receiver, working at about 130Ohm, coupled to one optical fibre (fig. 2) . The data produced by each floor are transmitted, at the same time, by two lasers: the laser (1555nm) coupled to the fibre connected to the floor and the laser (1535nm) coupled to the
250
E.G Anassontzis et aL INuclear Physics B (Proc. Suppl.) 66 (1998) 247-251
fibre connected to an adjacent floor. In this way we gain then a factor of two in safety and in the redundancy of the transmitted data. 3.3. Electronics The electronics that we have developed [10] and constructed to acquire the PMT pulses is able to transmit to the shore laboratory, in real time, the complete pulse of each PMT signal, maintaining the time coherence between PMTs. This electronics allows: 1) the knowledge of the pulse shape of each PMT (each PMT is served by a Flash ADC) 2) a real time control of the behaviour of each single PMT (for each PMT it is possible, from the shore, to control the HV and to vary the pulse threshold level) 3) to decide the trigger logic on shore, having so the maximum flexibility.
SO
Co~ant ~ean
70 60
/~
40
~
9.072 / 6 64.72 ~03,8 166.__~1 O.
!
30 2O
102
~02.5
103
103.5
104
10~..5 105 105.5 MEASURED DELAv (ns) {r'/nd' 11.08 / 8 Co~*stant 63.58 Vean 217.8
70 60
S:gmo
0.1832
50 4C 30 20 10 0
216
Ill'l'
, I . z
216.5
217
i .... 217.5
i , i~,
218
; .... i .... I 218.5 219 2~9.5 MEASURED DELAY (ns)
Figure 3. Measured time difference for the same pulse sent, with fixed delays, in two different daughter cards. The distribution on top refers to a fixed delay of ,-~ lOOns, the bottom one to a delay of ,~ 200ns
Each Optical Module will be served by a single card (called daughter card), the 14 daughter cards
of each plane are placed on a mother board and the whole is located in the Ti sphere at the center of each floor. In the mother board the asynchronous information coming from the PMT's are organised and synchronously transmitted on the fibre. Several daughter cards have been produced and successfully tested. According to the specifications they have a dynamic range greater then 1000 (the range selected is from one quarter of p.e. to 400 p.e.), they allow an average PMT single rate bigger than 1 5 0 k H z and to sample the PMT pulse each 5ns. Two mother card have been produced and successfully tested. Each mother board allows the multiplexing (in time) of the 14 PMTs data and the transmission of a serial flux of data at 400Mb/s. To qualify our electronics we measured the resolution in the measurement of the time difference for pulses recorded by different daughter cards. With the 5 n s samplings we reconstruct the PMT pulse shapes then we estimate, for each pulse, the threshold crossing time. We found that the resolution in time is well below l n s and independent from the time delay (fig. 3). The on-shore receiving electronics consists in the optical receiver card, one card (called MEZZANINE) that transforms the 400Mb/s serial link irrto a 10Mword/s (40 bit words) flux of data and that is mounted on a commercial PAMETTE card (DIGITAL). The PAMETTE card, mounted on a PCI bus, is used to provide the zero suppression, the extraction of the time and pulse information of each PMT, then it allows the trigger formation. Each mother board transmits also the information of the Slow Control Sensors that will be located close to the floor to which they belong. The signals of these sensors are first acquired and conditioned by a Slow Control System [11] that has been designed by the Collaboration. A Slow Control unit is based on a microcontroUer equipped with external R O M and R A M , plus an additional boards, developed by the Collaboration, containing the interface with the pulses. A prototype card has been successfullytested and used in real tests.
E.G. Anassontzis et al./Nuclear PhysicsB (Proc. Suppl.) 66 (1998) 247-251 4. Conclusions During the past two years NESTOR Collaboration made great progresses. The Construction of Optical Modules is a well established and successful operation: more than 40 OM have been already constructed and tested. The mechanical structure for three floors has also been constructed and tested. A deployment operation of a two floor structure has been carried on in shallow (~ 40m depth) and in deep water (~ 2500m depth). The electronics for data acquisition (for PMTs and for Slow Control Sensors) and for the transmission on optical fibres has been finalised. Tests made on first prototypes have been fully satisfactory. Cards needed for the first two floors are under construction. We plan to be soon operational. REFERENCES 1. Proceedings of the 2na NESTOR International Workshop, ed. L.K. Resvanis (University of Athens,1992) 2. Proceedings of the 3rd NESTOR International Workshop, ed. L.K. Resvanis (University of Athens,1993) 3. A. Capone et al. In Proceedings of the 2~th International Cosmic Ray Conference , Rome, Italy, (1995) 4. S. Bottal et al. In Proceedings of the 24th International Cosmic Ray Conference , Rome, Italy, 1 (1995) 1080 5. L.K.Resvanis et al.: NESTOR, A Neutrino Particle Astrophysics Underwater Laboratory for the Mediterranean, High Energy Neutrino Astrophysics Workshop, Hawaii, March 1992, V.J.Stenger, J.G.Learned, S.Pakvasa and X.Tata editors, World Scientific (1992), p. 325. 6. S.A. Khanaev and A.F. Kuleshov, in: Proceedings of the 2nd NESTOR International Workshop, Fortress of Niokastro, Pylos, Greece, 19-21 October, 1992, edited by L. K. Resvanis (Physics Laboratory, University of Athens, Athens, 1993), p. 253. 7. E. Anassontzis et al., NucL Instruments and Methods A 349 (1994) 242.
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8. T.A. Demidova and I. A. Repin, in: Proceedings of the 2nd NESTOR International Workshop, Fortress of Niokastro, Pylos, Greece, 19-21 October, 1992, edited by L. K. Resvanis (Physics Laboratory, University of Athens, Athens, 1993), p. 284. 9. E. Trimonis and M. Rudenko, in: Proceedings of the 2nd NESTOR International Workshop, Fortress of Niokastro, Pylos, Greece, 19-21 October, 1992, edited by L. K. Resvanis (Physics Laboratory, University of Athens, Athens, 1993), p. 321. 10. M. Bonori et al. In NESTOR data transmission, Dipartimento di Fisica, Universita di Roma "La Sapienza", Nota Interna n. 1055, 25 maggio 1995 (1995) 11. P. Locchi, A. Martini and L. Trasatti, in First Test of CRONOS, the NESTOR Slow Control System, LNF-97/004 (IR), (1997)