1. Optical Module
Procedure of assembly

2. Optical Module in NEMO Phase-2
ISEG
TIM-CAL
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)
FEM
13” OM sketch: lateral view

3. Optical Module in NEMO Phase-2
13” OM Lateral view 90° turned
Pressure gauge
12-pin connector
FEM
Optical fibre
Pressure gauge
12-pin connector (SEACON)
Special OMs :
LED beacon
PORFIDO
Piezo

4. 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
(>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

5. ISEG PMT base PHQ7081-i-2m (modified)
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 : 2000 Volts
Modified on the ouput on NEMO requiremts
Picture of the ISEG base soldered
Modifications on ISEG base

6. Magnetic shield
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
The cage around the 10” PMT
Picture of the parts of the cage

7. Facility to assemble the optical module
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
Device to mix the two component of the gel

8. OM assembly procedure: base soldering
Soldering of the ISEG base on the PMT
Base soldering
Mechanical Frame
Base positioning
Wires cut off
The end

9. 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 :
- 250mbar (15 mim)
- air reentry

10. OM assembly procedure: optical gel mixturing
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
- 250mbar (3 mim)
- air reentry

11. Picture of outgassing of the gel into the sphere
3 cycles of outgassing remove the air-bubble inside the gel .

12. OM assembly procedure: PMT positioning
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 atmosferic pressure and room temperature (12 h)
Mechanical support for PMT base and centering cross
PMT positioned in the glass sphere
PMT mounted on the centering cross

13. Assembled OM
Picture of an assembled hemisphere: glass, PMT, Gel, mu-metal cage, ISEG

14. Mechanical support for FEM electronic board and TIM-CAL
The mounted FEM
The mounted TIM-CAL

15. The 13” OM assembled with the 10” R7081 PMT
Picture of the OM with FEM and TIM-CAL and optical fibre
Picture of the optical module

16. Cablaggio delle connessioni elettriche per la semi-sfera nera
Il Modulo Ottico interamente connesso ( ma non chiuso ) viene testato:
comunicazione EFCM-FCM-FEM, accensione FEM, accensione PMT, rate in dark PMT
accensione e funzionamento Tim-Cal ( tramite Tim-Controll)
Accensione e funzionamento LED beacon, Porfido , Piezo

17. Closure of the OM Sealing of the OM :
hemisperes were aligned and joined
closed under-pressure at 250 mbar
external adhesive (Terostat) and
final check of the whole OM

18. Test in Hyperbaric 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
container with weights to keep OM in the bottom of the chamber
Results:
No lack of vacuum inside OM
No water inside OM
No detachment of the gel

19. 10 inch. vs. 8 inch R7081 Hamamatsu (10” STD): 10 inch. photocathode
Standard bialkali photocathode
(QE ≈ 400nm)
box and line with 10 stages
Length ≈ 300 mm max
R5912 HQE Hamamatsu (8” HQE):
8 inch. photocathode
Super bialkali photocathode
(QE ≈ 400nm)
box and line with 10 stages
Length ≈ 275 mm max
Sketch of 10 in. PMT. (courtesy of Hamamatsu K.K.)
Sketch of 8 in. PMT. (courtesy of Hamamatsu K.K.)

20. 8 inch super bialkali photocathode
Aumentando l’efficienza quantica si ha che il PMT 8 inch superbialkali (QE ≈ 400nm) ha una efficienza di rivelazione confrontabile con il 10 inch standard bialkali (QE ≈ 400nm)
Possibilità 1: data la minore lunghezza dell’8” ci sarebbe lo spazio per montare sulla base ISEG un socket per sostituire l’operazione di saldatura

21. 8 inch super bialkali photocathode
Possibilità 2: data la minore dipendenza rispetto al campo magnetico terrestre si potrebbe realizzare un OM senza l’utilizzo della gabbia magnetica
Semplificazione e riduzione tempi dell’assemblaggio
Riduzione del costo del singolo OM
Il PMT superbialkali presenta una frazione di after pulse tipo 2 ( impulsi spuri from 100ns to 16 us after main pulse ) dell’ordine del 15% ( rispetto al 5% su uno standard bialkali PMT)

22. Measurements of the effects of the Earth’s magnetic field
Every PMTs was measured in 3 inclinations:
- vertical downwards ( Tilt = 0° ) ; 50° downwards ( Tilt = 50° ); horizontal ( Tilt = 90° )
North 0°
Horizontal
angles
90°
270°
180°
Tilt : 50° Z
Vertical
axes
North 0°
Horizontal
angles
90°
270°
180° Z
Vertical position
Tilt : 0°
Vertical
axes
North Z
90°
270°
180°
Horizontal position
Tilt : 90°
Vertical axes 0°
Horizontal angles
Tilt
NORTH
PMT downwards
Dy 1
Dy 2
90°
270°
180° 0°
Top view
For each inclination, the PMT under test was rotated 360° around its vertical axis in 30° steps
Each PMT started its rotation from the same position with respect to the box and to the Earth’s magnetic field
Starting position for each PMT

23. Detection efficiency 8” SBA PMT (HQE) vs. 10” standard PMT :
Without µ-metal cage the 8” SBA PMT can lose up to 15% in Relative Efficiency and P/V ratio (especially for 50° and horizontal inclinations). The others parameters are less influenced.
Both equipped with µ-metal cage, the 10” Std PMT shows a Relative Efficiency slightly higher than the 8” SBA PMT (+5% on average over the angles and inclinations).

24. Gain 8” SBA PMT (HQE) vs. 10” standard PMT :
For any parameters and any PMT
the 50°direction is the one which shows the greater influence on the magnetic field.
As expected the 8” SBA PMT shows a lower dependency on Earth magnetic field than the
10” Std PMT

25. TTS 8” SBA PMT (HQE) vs. 10” standard PMT :
Averaged (over the angles and inclinations) the 8” SBA PMT has a TTS value which is around 1ns below the 10” Std.

26. Standard QE = QE min 20% at peak Prezzi unitari
Quotazione 8 inch super bialkali e 10 inch bialkali photocathode
HQE = QE min 32 % at peak
Standard QE = QE min 20% at peak
Prezzi unitari
8” R5912 HQE €; ( After pulse 2 <= 25 %)
8” R5912 HQE SEL € ( After pulse 2 <= 15 %)
consegna 70gg
Prezzi per un quantitativo pari a 2000pcs
8” R5912 HQE €; ( After pulse 2 <= 25 %)
8” R5912 HQE SEL € ( After pulse 2 <= 15 %)
10” R7081 standard QE € ( After pulse 2 <= 5 %)
consegna dall'ordine circa 3mesi per i primi 200pcs, i successivi con un rate di 200pcs/month ( in totale poco più di 1 anno).

27. Additional slides

28. Detection efficiency 0° 0° 50° 50° 90° 90° NAKED SHIELDED
In naked 8” PMTs the impact of the magnetic field was smaller than naked 10”
The shield reduced considerably the variations for the 10” PMT
The increased QE in the HQE 8” PMT compensates the smaller detection area respect to the 10”
90°
90°
NAKED SHIELDED

29. Gain
Greatest gain variation was less than 10% for both the naked 8”
Considerable variations in the 10” PMT naked, up to 29%
The shield reduces variations in both the 8” PMTs, with variations less than 4.4 %
The shield reduces strongly the variations in the 10” PMT, with variation less than 7%
NAKED SHIELDED

30. Peak to Valley ratio NAKED SHIELDED
Considerable variations for all the un-shielded PMTs
Great reductions in variation by using the magnetic shield
Small improvements in average values with the magnetic shield
NAKED SHIELDED

31. Charge Resolution (sigma)
Large effects of magnetic field for the unshielded 10” PMT
The mu-metal cage greatly reduced the variation in 10” PMT
No large effects due to the magnetic field for 8” PMTs.
The mu-metal cage reduced variations for both 8” PMTs
NAKED SHIELDED

32. TT NAKED SHIELDED No considerable effects of the mu-metal cage
No significant variations due to magnetic field for all the PMTs
No considerable effects of the mu-metal cage
Difference in average value due to the different size between 8” and 10” PMT
NAKED SHIELDED

33. TTS NAKED SHIELDED Variations over the 10% in all the un-shielded PMTs
Considerable reduction in variations with the magnetic shield
No significant improvement in average values with magnetic shield
NAKED SHIELDED