2Optical Module in NEMO Phase-2 ISEGTIM-CALA glass sphere 13” (Vitrovex):Single large area photomultiplier : Hamamatsu 10” PMT R7081Optical gel : Waker SilGel 612μ-metal wire cagePMT base circuit : ISEG PHQ7081-i-2m modifiedFEM (Front End Module) electronic boardSystem for timing calibration (TIM-CAL)FEM13” OM sketch: lateral view
3Optical Module in NEMO Phase-2 13” OM Lateral view 90° turnedPressure gauge12-pin connectorFEMOptical fibrePressure gauge12-pin connector (SEACON)Special OMs :LED beaconPORFIDOPiezo
4Glass spherestandard 13 inches deep-sea instrumentation vessels in borosilicate glass, produced by Vitrovextwo half spheres: ½ transparent, ½ painted blackno vacuum valveunique penetration for the 12-pin connectorRefractive index(>350 nm)Transmission>95% (>350 nm)Density at 20 0C2.23 g cm-3Thermal conductivity1.2 W m-1K-1Characteristics of 13 inches spheresDepth rating (m)10000Overall diameter (mm)330Wall thickness (mm)11Mass (kg)7.89Buoyancy (empty) (N)114Diameter shrinkage per 1000m depth (mm)0.30
5ISEG 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 controllableAnode current max : 100 microAmperePower consumption : 2000 VoltsModified on the ouput on NEMO requiremtsPicture of the ISEG base solderedModifications on ISEG base
6Magnetic shieldA 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 diameterpitch of 68 x 68 mmshadow on the photocathode ≈ 5%average shielding factor measured ≈ 4The cage around the 10” PMTPicture of the parts of the cage
7Facility to assemble the optical module 2 plexiglass vacuum boxes : 1x1x1 m, 300 mbar in less than 2 minutesPurposes:degassing of the optical gelclosing the two hemispheres of the OMplace where gluing PMT+ metal cage on the glass sphereDevice to mix the two component of the gel
8OM assembly procedure: base soldering Soldering of the ISEG base on the PMTBase solderingMechanical FrameBase positioningWires cut offThe end
9OM assembly procedure: cleaning cleaning of each element: optical paper and methyl alcohol- inner surface of the hemi-spheres- mu-metal cagemu-metal cage positioned into the glasshemisphere1 cycle of outgassing :- 250mbar (15 mim)- air reentry
10OM 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 hemisphere3 cycles of outgassing- 250mbar (3 mim)- air reentry
11Picture of outgassing of the gel into the sphere 3 cycles of outgassing remove the air-bubble inside the gel .
12OM assembly procedure: PMT positioning PMT mounted on the centering cross by means of a properly supportpositioning into the sphere by means of the centering cross3 cycles of outgassingPolimerization of the atmosferic pressure and room temperature (12 h)Mechanical support for PMT base and centering crossPMT positioned in the glass spherePMT mounted on the centering cross
13Assembled OMPicture of an assembled hemisphere: glass, PMT, Gel, mu-metal cage, ISEG
14Mechanical support for FEM electronic board and TIM-CAL The mounted FEMThe mounted TIM-CAL
15The 13” OM assembled with the 10” R7081 PMT Picture of the OM with FEM and TIM-CAL and optical fibrePicture of the optical module
16Cablaggio 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 PMTaccensione e funzionamento Tim-Cal ( tramite Tim-Controll)Accensione e funzionamento LED beacon, Porfido , Piezo
17Closure of the OM Sealing of the OM : hemisperes were aligned and joinedclosed under-pressure at 250 mbarexternal adhesive (Terostat) andfinal check of the whole OM
18Test 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 atmcontainer with weights to keep OM in the bottom of the chamberResults:No lack of vacuum inside OMNo water inside OMNo detachment of the gel
1910 inch. vs. 8 inch R7081 Hamamatsu (10” STD): 10 inch. photocathode Standard bialkali photocathode(QE ≈ 400nm)box and line with 10 stagesLength ≈ 300 mm maxR5912 HQE Hamamatsu (8” HQE):8 inch. photocathodeSuper bialkali photocathode(QE ≈ 400nm)box and line with 10 stagesLength ≈ 275 mm maxSketch of 10 in. PMT. (courtesy of Hamamatsu K.K.)Sketch of 8 in. PMT. (courtesy of Hamamatsu K.K.)
208 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
218 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 magneticaSemplificazione e riduzione tempi dell’assemblaggioRiduzione del costo del singolo OMIl 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)
22Measurements 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° )North0°Horizontalangles90°270°180°Tilt : 50°ZVerticalaxesNorth0°Horizontalangles90°270°180°ZVertical positionTilt : 0°VerticalaxesNorthZ90°270°180°Horizontal positionTilt : 90°Vertical axes0°Horizontal anglesTiltNORTHPMT downwardsDy 1Dy 290°270°180°0°Top viewFor each inclination, the PMT under test was rotated 360° around its vertical axis in 30° stepsEach PMT started its rotation from the same position with respect to the box and to the Earth’s magnetic fieldStarting position for each PMT
23Detection 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).
24Gain 8” SBA PMT (HQE) vs. 10” standard PMT : For any parameters and any PMTthe 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 the10” Std PMT
25TTS 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.
26Standard QE = QE min 20% at peak Prezzi unitari Quotazione 8 inch super bialkali e 10 inch bialkali photocathodeHQE = QE min 32 % at peakStandard QE = QE min 20% at peakPrezzi unitari8” R5912 HQE €; ( After pulse 2 <= 25 %)8” R5912 HQE SEL € ( After pulse 2 <= 15 %)consegna 70ggPrezzi per un quantitativo pari a 2000pcs8” 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).
28Detection 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” PMTThe increased QE in the HQE 8” PMT compensates the smaller detection area respect to the 10”90°90°NAKED SHIELDED
29GainGreatest 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
30Peak to Valley ratio NAKED SHIELDED Considerable variations for all the un-shielded PMTsGreat reductions in variation by using the magnetic shieldSmall improvements in average values with the magnetic shieldNAKED SHIELDED
31Charge Resolution (sigma) Large effects of magnetic field for the unshielded 10” PMTThe mu-metal cage greatly reduced the variation in 10” PMTNo large effects due to the magnetic field for 8” PMTs.The mu-metal cage reduced variations for both 8” PMTsNAKED SHIELDED
32TT NAKED SHIELDED No considerable effects of the mu-metal cage No significant variations due to magnetic field for all the PMTsNo considerable effects of the mu-metal cageDifference in average value due to the different size between 8” and 10” PMTNAKED SHIELDED
33TTS NAKED SHIELDED Variations over the 10% in all the un-shielded PMTs Considerable reduction in variations with the magnetic shieldNo significant improvement in average values with magnetic shieldNAKED SHIELDED