Optical Module Procedure of assembly

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

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

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

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 : 150mW @ 2000 Volts Modified on the ouput on NEMO requiremts Picture of the ISEG base soldered Modifications on ISEG base

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

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

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

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

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

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

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 gel @ 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

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

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

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

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

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

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

10 inch. vs. 8 inch R7081 Hamamatsu (10” STD): 10 inch. photocathode Standard bialkali photocathode (QE ≈ 25% @ 400nm) box and line with 10 stages Length ≈ 300 mm max R5912 HQE Hamamatsu (8” HQE): 8 inch. photocathode Super bialkali photocathode (QE ≈ 32% @ 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.)

8 inch super bialkali photocathode Aumentando l’efficienza quantica si ha che il PMT 8 inch superbialkali (QE ≈ 32% @ 400nm) ha una efficienza di rivelazione confrontabile con il 10 inch standard bialkali (QE ≈ 25% @ 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

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)

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

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).

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

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.

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 2.38€; ( After pulse 2 <= 25 %) 8” R5912 HQE SEL4 2.73€ ( After pulse 2 <= 15 %) consegna 70gg Prezzi per un quantitativo pari a 2000pcs 8” R5912 HQE 1.242€; ( After pulse 2 <= 25 %) 8” R5912 HQE SEL4 1.431€ ( After pulse 2 <= 15 %) 10” R7081 standard QE 1.521€ ( 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).

Additional slides

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

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

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

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

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

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