Catania

Assembly and Design of the Optical Modules for the NEMO Phase-2

E. Leonora, S. AielloINFN, sez. Catania

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 2

NEMO Phase-2

It consists of new infrastructure at the deep-sea site of Capo Passero, Sicily, at 3500 m depth :

- 100 km cable, linking the site to the shore

- a shore station, inside the harbor of Portopalo of Capo Passero

- the underwater infrastructures need to connection

- the prototype of the detector :

- 8 storeys tower

- 2 Optical Modules (OMs) at each end

( Vertical, Horizontal)

- 4 OMs per storey

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 3

Optical Module in NEMO Phase-2

• A glass sphere 13” (Vitrovex):

• Single large area photomultiplier : Hamamatsu 10” PMT R7081

• Optical gel : Waker SilGel 612

• μ-metal wire cage

• PMT base circuit : ISEG PHQ7081-i-2m modified

• FEM (Front End Module) electronic board

• System for timing calibration (TIM-CAL)

13” OM sketch: lateral view

TIM-CAL

FEM

ISEG

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 4

13” OM Lateral view 90° turned

Pressure gauge

12-pin connectorFEM

Optical fibre

Optical Module in NEMO Phase-2

• Pressure gauge

• 12-pin connector (SEACON)

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 5

Glass sphere

• standard 13 inches deep-sea instrumentation vessels in borosilicate glass, produced by Vitrovex

• two half spheres: ½ transparent, ½ painted black

• no vacuum valve

• unique penetration for the 12-pin connector

Refractive index 1.48 (>350 nm)

Transmission >95% (>350 nm)

Density at 20 0C 2.23 g cm-3

Thermal conductivity 1.2 W m-1K-1

Characteristics of 13 inches spheres

Depth rating (m) 10000

Overall diameter (mm) 330

Wall thickness (mm) 11

Mass (kg) 7.89

Buoyancy (empty) (N) 114

Diameter shrinkage per 1000m depth (mm)

0.30

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 6

Large area photomultiplier

R7081 Hamamatsu: • 10 inch. photocathode• Standard bialkali photocathode (QE ≈ 25% @ 400nm)• 10 stages

A batch of 72 PMTs was bought and characterized

Picture of a test box

Dimensions of the R7081(Courtesy of Hamamatsu)

Sketch of test apparatus

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 7

  mean value

values range

Voltage at Gain 5E7 [V] 1655 1595÷1775

Dark Count rate [Hz] 1388* 674÷3000*

P/V ratio 3.5 2.6÷4.3

Charge resolution σ % 31.6 23.5÷ 41.4

TTS FWHM [ns] 2.8 2.5÷3.3

Pre-Pulse % 0.02 0.001÷ 0.11

Late Pulse % 5.5 3.8÷6.6

Type 1 after pulse % 1.1 0.8÷1.9

Type 2 after pulse % 4.4** 2.2÷7.3**

Procedure and results of measurements were published on NIM A: S.Aiello, E. Leonora et al. Nucl. Instr. Meth. A, 614 (2010) 206-212

Measurements on 72 R7081 Hamamatsu PMTs

* Excluding one PMT with DC rate of 4093 Hz

** Excluding one PMT with type 2 after pulse fraction of 10.4%.

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 8

Main features: • Active base• +5 Volts supply (bipolar voltage supply before modification) • Cathode-1^dynode and 1^dynode-anode voltages individually controllable • Anode current max : 100 microAmpere • Power consumption : 150mW @ 2000 Volts• Modified on the ouput on NEMO requiremts

ISEG PMT base PHQ7081-i-2m (modified)

Picture of the ISEG base solderedModifications on ISEG base

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 9

Effect on the anode signal of the ISEG modification

The same signal obtained with the damping resistors

- no ringing in the signal

- increase in signal rise time and width

- saturation starts around at 100-120 p.e.

- limit about 1 nC for laser pulsed (width of 60 ps)

1 p.e typycal signal from Hamamatsu R7081with the ISEG base

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 10

Purposes :• Optical link between PMT photocatode and glass sphere• Mechanical assembly of the PMT with the glass sphere.

Main requirements:

• High trasparency

• Refractive index close to that of sphere and PMT window

• Good rigidity to hold the OM components with a sufficiently elastic properties to absorb shocks

• Properties should be stable over 10-year period

Waker SilGel 612 two components (A e B) (silicone gel)

Tests on 4 different mixtures 40B/100A, 50B/100A, 60B/100A, 70B/100A

Optical Gel

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Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 11

mixtureSilGel

40B/100A

50B/100A

60B/100A

70B/100A

absorption length at 400 nm

12 cm 30 cm 33 cm 35 cm

mixtureSilGel

40B/100A

50B/100A

60B/100A

70B/100A

Transmittanceat 400 nm

85% 93.8% 94.3% 94.7%

Silgel Optical Properties measurements

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 12

mixtureSilGel 40B/

100A50B/100A

60B/100A

70B/100A

Refraction index at 400

nm 1.43 1.50 1.47 1.38

Good matching with the glass sphere (n=1,48 at 350÷450

nm)for ratios 50B/100A and 60B/100A

The selected silgel mixture

Considering optical testsand mechanical tests

mixture chosen was 50B/100A

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 13

A cage of mu-metal wire was chosen as magnetic shield (ITEP, Moscow):• a hemispherical part ( 30 cm diameter, 14 cm height)• a flat part (30 cm diameter ) with a hole in its centre ( 12 cm diam.)• wire of 1 mm of diameter• pitch of 68 x 68 mm • shadow on the photocathode ≈ 5%• average shielding factor measured ≈ 4

Magnetic shield

Picture of the parts of the cage The cage around the 10” PMT

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 14

The influence of the Earth’s magnetic field, and the effect of the mu-metal cage, was studied on the 10” PMT for three different inclination: vertical downwards (0°), horizontal (90°), and tilted of 50°

Effects of the mu-metal cage on PMT : facilities

A dark box able to rotate with respect to vertical axes (1° step) and to change its inclination (10 °step) was realized.

No magnetic materials were used in its constructions

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 15

• The magnetic shielding reduced strongly the variations in the PMT and even improved performance.

Further information on E. Leonora, “Terrestrial Magnetic Field Effects on Large Photomultipliers” in this Workshop

Effects of the mu-metal cage on PMT : results

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 16

2 plexiglass vacuum boxes : 1x1x1 m, 300 mbar in less than 2 minutes

Purposes:

• degassing of the optical gel

• closing the two hemispheres of the OM

• place where gluing PMT+ metal cage on the glass sphere

Picture of the vacuum boxes

Facility to assemble optical module

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 17

Soldering of the ISEG base on the PMT

Mechanical Frame Base positioningBase soldering

Wires cut off

The end

OM assembly procedure: base soldering

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Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 18

OM assembly procedure: cleaning • cleaning of each element: optical paper and methyl alcohol

- inner surface of the hemi-spheres- mu-metal cage

• mu-metal cage positioned into the glass hemisphere

• 1 cycle of outgassing :- vacuum @ 250mbar (15 mim)- air reentry

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Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 19

• mixture gel preparation 1.5 litre x OM: 1 lltre A + 0,5 litre B at 120 giri/min.

• pouring the gel into the glass hemisphere• 3 cycles of outgassing

- vacuum @ 250mbar (3 mim)- air reentry

OM assembly procedure: optical gel mixturing

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 20

Picture of outgassing of the gel into the sphere

3 cycles of outgassing remove the air-bubble inside the gel .

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 21

• PMT mounted on the centering cross by means of a properly support• positioning into the sphere by means of the centering cross• 3 cycles of outgassing • Polimerization of the gel @ atmosferic pressure and room temperature (12 h)

OM assembly procedure: PMT positioning

Mechanical support for PMT base and centering cross

PMT mounted on the centering cross

PMT positioned in the glass sphere

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 22

Assembled OM

Picture of an assembled hemisphere: glass, PMT, Gel, mu-metal cage, ISEG

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 23

Mechanical support for FEM electronic board and TIM-CAL

The mounted FEM The mounted TIM-CAL

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 24

The 13” OM assembled with the 10” R7081 PMT

Picture of the optical fibre for calibrationPicture of the OM with FEM and TIM-CAL

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 25

Closure of the OM

Sealing of the OM :• hemisperes were aligned and joined• closed under-pressure at 250 mbar • external adhesive (Terostat) and tape

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 26

Test pressure profile

0

50

100

150

200

250

300

350

400

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Time [ hours ]

Pre

ss

ure

[B

ar]

container with weights to keep OM in the bottom of the chamber

The watertight and mechanical resistance of the OM assembled was tested in the hyperbaric chamber of NEMO test site (Catania harbour) up to 350 atm

Test in Hyperbaric Chamber

Results:

No lack of vacuum inside OM

No water inside OM

No detachment of the gel

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 27

Conclusion

• 13” Optical Modules with single large 10” PMT was designed

• Each single component was chosen after intense phase of test:

- test on PMTs

- test on the base for Voltage Supply

- test on optical gel

- test on a mu-metal cage as magnetic shield

• A definitive procedure of assembly was defined

• 32 OM were assembled

• Tests in Hyperbaric chamber were done

• experimental OMs ( Acoustic OM, LED-Beacon, PORFIDO system)

The OMs will be deployed soon in NEMO Phase-2

Catania

Erlangen 12-14 October 2011 emanuele.leonora@ct.infn.it 28