The eyes of ANTARES

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The eyes of ANTARES

• Pascal VERNIN
• From Jean-Pierre SCHULLER
• CEA Saclay/DAPNIA
• VLVnT workshop, Amsterdam, 5/10/2003

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Outline

• Detector Design
• The optical modules
• Requirements
• PMTs
• Accessories magnetic shielding, base and so on
• Assembly and final checks
• Optical module in sea water
• Conclusions

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The 0.1 km2 Detector
Shore station
2500m
60m
Acoustic beacon
buoy
Electro-optic submarine cable 50km
350m active
12m
Electronics containers
100m
Junction box
anchor
Readout cables
12 lines 1 instrumented line
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Optical modules - Requirements (1)

• Hemispherical photo-cathode
• Sensitive area as large as possible

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Optical modules - Requirements (2)

• Limiting factors for the size
• Mechanics housing high pressure sphere 17
• Noise (proportional to surface) reconstruction
  efficiency
• Spread of transit time time measurement

But, ageing!?
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Optical modules - Requirements (3)

• Ageing test

Duration of the test eq. to gt 10 years of Antares
running
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Optical modules - Requirements (4)

• Energy measurement capability
• Clear spe spectrum
• Lower limit on peak/valley ratio

• Resolution of multi-hit
• Constraints in signal timing

• Reconstructions efficiency
• Upper limit on dark count
• Upper limits on fake signals

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Optical modules PMTs Specs
To summarise

• Sensitive area ? 500 mm2
• (quantum ? collection) efficiencies gt 16
• Amplification 2. 108 for HV lt 2500 V

At working point (? amplification 5. 107)

• Transit time spread lt 3.6 ns (FWHM)
• Dark count (_at_ 0.3 spe) lt 10 kHz
• Peak/valley gt 2
• Shape of signal tr lt 5 ns tw lt 12 ns and tf lt 15
  ns
• Pre, late and after pulses lt 1 , 2, 10

in the window .1, 16 ms after
in the window 10, 100 ns after
in the window -100, -10 ns before the true pulse
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Optical modules PMTs Selection

• Commercially available PMTs (97)
• E.T.L. 8
• Hamamatsu 8, 10, 15, 20
• Photonis 9

• The candidates

• Proposed developments
• E.T.L. 11
• Hamamatsu 13
• Photonis 12

• The winner is

10 Hamamatsu
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Optical modules - Systematic checks

• 900 tubes delivered
• Control of specs on all PMT

• Scanning of photo-cathode (for some)

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Optical modules - Systematic checks

• 900 tubes delivered
• Control of specs on all PMTs
• rejection lt 2 always due to P/V ratio 1.9 or
  1.85 instead of 2 !
• very constant quality

One batch 100 PMTs
Rectangular box rms

• Scanning of photo-cathode (for some)

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Optical modules - Magnetic shielding (1)

• Earth magnetic field influences the trajectory of
  photo-electrons especially between photo-cathode
  and 1st dynode
• Effect on collection efficiency
• depends on PMT orientation w.r.t. field
• increases of the non-uniformity of the response
  over the sensitive area

? Magnetic shielding needed
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Optical modules - Magnetic shielding (2)

• Foil of ?-metal excluded !
• cage
• Size of mesh and wire diameter
• compromise between field reduction and shadowing
  effects

• Cage ?-metal wire
• ?R ? 105
• ? 1.08 mm
• Mesh 68 mm x 68 mm

Reduction factor of transverse field components
gt 3
Prod. by ITEP-Moscow
Improvement on uniformity cf. previous slide
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Optical modules - Magnetic shielding (3)

• Improvements on the P/V ratio and TTS

Rem this TTS includes the 1 ns width of the
light source!
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Optical modules - Bases (1)

• Passive base cascade of resistors
• Consumption of 3 W too large
• Active base Cockcroft-Walton cell

• Main (common) characteristics

• Power supply 48 V
• 800 V (fixed) between PK and D1
• Pilot voltage 0 to 1.5 V (0 to 1500 V between D1
  and last dynode)
• Output for anode, last dynode and last but 2
  dynode
• Noise lt 5 mV pp on output
• Consumption ? 300 mW

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Optical modules - Bases (2)

• Linearity VAD vs. vset

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Optical modules - Time calibration (1)

• Motivation
• the transit time is one of the components that
  give the signal timing
• It is related to the true high voltage applied to
  the PMT

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Optical modules - Time calibration (2)

• Question 1
• TT is measured with uniform illumination of all
  the photo-cathode
• This system illuminate only the central part of
  the photo-cathode
• The results are comparable ?

shift 0.3 ns ? OK

• Question 2
• How the Al coating thickness is reproducible ?

• On the same tube
• Ok within a factor 2 (in light transmission)
• (measured o.d. ? 4)
• For ? tubes
• very similar
• (systematic measurements on the way)

VAD vs. TTV - TTVref (ns)
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Optical modules - Assembly (1)
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Optical module - Assembly (2)
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Optical module - Assembly (3)
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Optical modules - Final checks

• Before an optical module is declared good, simple
  functional tests are done
• Spe amplitude
• LEDs response

• And by sampling
• Scanning

• Environnemental tests (to simulate transportation
  and sea operations)
• Vibrations
• Temperature cycling

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Optical properties of sea water
Water transparency
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Optical background in sea water

• On 10 PMt
• 60 kHz from 40K - b- decay bacteria (_at_ .3 spe
  threshold)
• MHz bioluminescence bursts (rise time few ms,
  duration 1 s)
• ? Dead time lt 5

102?
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Conclusions and future

• 900 tubes delivered
• Exhibit good performances and constant quality
  level
• Production of optical modules started smoothly

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F I N E
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The Sector Line
Optical Module
Local Control Module
Optical module frame
Junction Box
InterLink cable
to shore station
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The Mini Instrumentation Line
Mechanical Cable

• Current profiler
• ADCP 300 kHz of RDI
• Orientated downwards
• Current profile for 150 m
• Resolution 0.5 cm/s
• RS232 interface
• Temperature/Salinity
• Modèle 37-SI MicroCAT
• Resolution 10-4 C, 10-4 S/m
• RS232 interface
• Transmissionmeter
• CSTAR of Wetlabs
• Measures over 25cm
• Analog response

Sound Velocimeter
ADCP
Electro Mechanical Cable 3 fibres for DAQ
100m
Acoustic Positioning Modules (receivers)
Optical Beacon
CTD
CSTAR
Electro Mechanical Cable 2 fibres for DAQ, 1 for
clock
100m
LASER Beacon
Acoustic Positioning Modules
2 fibres for DAQ 1 for clock
JB
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Sphere Implosion Test
Pascal COYLE Les Houches Jan 2002

• Stored potential energy in sphere at 2600m
  V?P 1 mega Joule !!
• Risk of accidental implosion provoking a
  catastrophic chain
• reaction (a la SuperKamiokande)

Tests (June 2000) Two storeys 12m apart, 1
sphere weakened, implosion occurred at a depth of
2600m
AFTER
BEFORE

• RESULT
• -Neighbouring spheres on same
• storey also imploded
• Electronics in LCM destroyed
• Upper storey intact
• Mechanical cable unbroken

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Installations in La Seyne sur Mer
Detector Assembly Hall Foselev Marine
La Seyne sur Mer
Land Cable ( Fibre optics )
Power Hut Les Sablettes
Submarine cable (Fibre optics power )
Shore Station Villa Michel Pacha
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Degradation of light signal glass sphere
bio-fouling
For q gt 90º transmission loss lt 1.5 in 1 yr
(and saturates)