Timing Calibration of the NEMO Optical Sensors

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Timing Calibration of the NEMO Optical Sensors

• G. Caporaletti, M. Circella, C. De Marzo, M.
  Ruppi
• Istituto Nazionale di Fisica Nucleare, Bari
• on behalf of the NEMO Collaboration

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NEMO Neutrino Mediterranean Observatory Collaborat
ion
INFN Bari, Bologna, Cagliari, Catania, Genova,
LNF, LNS, Napoli, Pisa, Roma CNR Istituto di
Oceanografia Fisica, La Spezia Istituto di
Biologia del Mare, Venezia Istituto Sperimentale
Talassografico, Messina Istituto Nazionale di
Geofisica e Vulcanologia Istituto Nazionale di
Oceanografia e Geofisica Sperimentale Universitie
s Bari, Bologna, Cagliari, Catania, Genova,
Napoli, Pisa, RomaLa Sapienza
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Neutrino Telescopes
We want to measure neutrinos coming from
astrophysical sources
The apparatus is deployed at large depth undersea
to reduce the background from charged particles.
Neutrinos are searched by detecting particles
arriving from the bottom
neutrino
Cherenkov light
muon
3500m depth
The tracks of muons produced from interacting
neutrinos are reconstructed from the measurements
of Cherenkov light collected by a grid of sensors
neutrino
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NEMO Telescope layout
Tower
Secondary JB

• 1 primary Junction Box
• 8-9 secondary Junction Boxes
• 64-81 towers
• 140 m grid pitch
• 64-72 PMT on each tower
• 4096-5832 PMT in total

Primary JB
1120-1440 m
Huge apparatus of more than 1 km side and 800 m
tall
140-180 m
140-180 m
Electro-optical cable to shore
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NEMO Phase 1 project
A prototyping activity of realization of a
detector subsystem including all critical
components
UNDERWATER LAB TEST SITE
SHORE LABORATORY Catanias port
EO CABLE Already deployed, it connects the shore
station to the undersea test site Length 25
km 10 Optical Fibers ITU- T G-652 6 Electrical
Conductors
About 20km off the Catania coast
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Tower Layout
FCM (Floor Control Module)

• Optical Module
• ( FE electronics)

Data from OM are collected in FCM and delivered
over an optical fiber in a dedicated DWDM
wavelength to shore (the path is completely
passive between the shore and each FCM)
750 m
Junction Box
DWDM mux
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Time calibration in NEMO (the approach)
Floor Control Module
Goal determine the offsets in local time
measurements (relative timing calibration)
Optical Module ( FE electronics)
Tower JB
Secondary JB
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Optical calibration system
Optical Module
diffuser
Optical fibre
splitter
A command coming from shore activates a light
pulse from a pulser in the FCM. This light pulse
is delivered to the OM of one floor over a
network of optical fibers.
Pulser
Optical source
FCM (Floor Control Module)
FCM electronics interface
shore
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The Pulser
LED
C2
R3
R1
C1
Q1
Q2
Vi
R2
Among several configurations of the pulser
circuit that we have studied, simulated and
implemented, we have finally selected one, very
simple yet very performing
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The Pulser
Agilent HLMP CB15 InGaN Blue LED Peak Wavelength
472 nm Viewing angle 15
LED
C2
R3
R1
C1
Q1
Q2
Vi
R2
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Optical coupling
Thorlabs F220FC-A
Optical power picked up from the fiber has been
optimized by means of an optical collimator
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Optical fiber

• An extensive evaluation of the
• performance of different fibers
• (monomode and multimode)
• was done.
• The optimal fiber for this
• application has to be
• Multimode (small intermodal
• dispersion in few tens meters)
• Large NA
• Large core

Selected fiber Thorlabs ASF50/125 Multimode
0.22 NA Core 50 ?m
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The sensor used for the tests
Module PMT Hamamatsu H6780 Rise time 0.78 ns
5.5 cm

• Advantages of this sensor
• Fast
• Low TTS (0.28ns)
• Compact
• High-voltage power supply implemented inside the
  module
• Easy to use

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Tests 1
Tests of pulser board Fiber 20m
Fall time 2.5 ns
FWHM lt 7 ns
Standard deviation of time delay from trigger lt
100 ps
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Tests 2
Tests of pulser board Fiber 40m
Fall time 2.8 ns
FWHM 7.1 ns
Standard deviation of time delay from trigger lt
100 ps
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Tests 3
Tests of pulser board Fiber 20m splitter 2x4
Fall time 2.4 ns
FWHM 6 ns
Standard deviation of time delay from trigger
300 ps
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Tests 4
Hamamatsu PLP-10 LED Head Peak power
3.7mW FWHM 5.4 ns Wavelength 464 nm
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Tests 5
Test conditions Fiber 20m Collimator F220FC-A
Pulser
trigger
PLP-10
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Future extension
To upper floor
We will offer redundancy to the "echo" timing
calibration by using the same optical pulser to
illuminate the sensors of more than one floor
From lower floor
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Conclusions

• The timing calibration in NEMO will be performed
  by
• I Echo calibration
• II Optical calibration
• The optical calibration system has been
  developed and extensively tested
• All tests made so far give good results
• An extension of the optical calibration system
  is currently under evaluation it will allow
  redundant measurements to the "echo" timing
  calibration
• The solution described in this work is
  functional, cheap and scalable to any neutrino
  telescope of km3 scale. It will be operated in a
  prototype tower of NEMO Phase 1 next year