Department of Physics and Astronomy, International Workshop on a Very Large Volume Neutrino Telescope for the Mediterranean Sea Department of Physics and Astronomy, Catania VLVnT08 - Toulon, Var, France, 22-24 April 2008 Characterization of a prototype of a new multianodic large area photomultiplier Leonora Emanuele INFN Catania on benhalf of NEMO collaboration Toulon, April 23 emanuele.leonora@ct.infn.it

The multianodic photomultiplier Two prototypes were tested : ZF0021; ZF0025 same shape of Hamamatsu R7081 (10’’) 4 anodic ouputs 4 separate amplification chains (10 dynode stages) Each anode is sensitive to one fourth of the photocathode area  PMT is a position sensitive photo-detector Drawing taken from Hamamatsu data sheets Picture of PMT Anodes identification (front view) For testing it was used a resistive voltage divider realized according to Hamamatsu Toulon, April 23 emanuele.leonora@ct.infn.it

The Testing Facility Measurements conditions: Dark box (2 x 1.7 x 1.5) m 410 nm Laser Source pulsed: width 60 ps, frequency range 0÷40 MHz PMT for test (naked or with μ-metal cage) Monitor PMT, to check stability of the light source during measurements Light source movement system, for scanning photocathode surface Dedicated code (LabView), to control movement and data acquisition Measurements conditions: PMT with μ-metal cage -room temperature and atmospheric pressure Picture of Dark box Drawn of source movement system. θ: vertical ; φ=orizzontal semicircular guide θ φ optical fibre carriage View of the Software Picture of PMT and light source movement system Toulon, April 23 emanuele.leonora@ct.infn.it

The prototype performances: Gain Gain has been measured studying for each anode the position of the single-photon electron peak as a function of HV value. Typical charge spectrum in single pe Experimental points for sample ZF0021 Similar behaviour for anode 1, 2, 3 The anode 4 presents a smaller gain: about - 25 % @ 1500 V for ZF0021 about - 20 % @ 1500 V for ZF0025 The dependence from the High Voltage is the same for all the anodes Different behaviour for Anode 4 could be related to dynods’ geometry Toulon, April 23 emanuele.leonora@ct.infn.it

The overall response. Linearity Response of the photomultiplier when the entirely photocatode is illuminated with a plane-wave pulsed beam, measured for each anode separately Voltage supply = 1550 Volt  Gain ≈ 5E7 Linearity Anode 1 of ZF0025 Picture of the pmt positioned to illuminate the whole photocathode Every anodes presents good linearity up to 100 photoelectrons The loss of linearity over the 100 photoelectrons was already measured in the standard R7081 PMTs Toulon, April 23 emanuele.leonora@ct.infn.it

The overall response. Charge and Timing Single photon charge spectrum Transit Time distribution in spe Discriminator threshold = 20 mV  1/ 3 spe Anode2 Anode A1 A2 A3 A4 P/V ratio 3.03 3.09 2.95 2.75 Gain [x 107] at 1550 V 5.0 5.4 3.9 σE / E % 33.62 30.62 37.34 35.15 TTS [ns] (FWHM) 4.62 3.95 3.54 4.16 Dark count rate (1/3 spe) ≈ 1Khz for each anode Summary of the ZF0025 properties Performances are comparable, except for gain of anode 4 Toulon, April 23 emanuele.leonora@ct.infn.it

Definition of Secondary Pulses According to Hamamatsu Toulon, April 23 emanuele.leonora@ct.infn.it

The overall response. Spurious pulses Typical Afterpulse 1 distribution Typical Afterpulse 2 distribution Pre pulses Delayed pulses Single pe typical Timing Distribution Anode A1 A2 A3 A4 Pre pulse [%] 0.05 0.18 0.24 Delayed pulse [%] 7.74 7.96 7.14 6.50 After Pulse 1 [%] 1.57 1.91 1.68 1.22 After Pulse 2 [%] 10.87 12.53 13.49 10.41 Summary of spurious pulses for ZF0025 Values are comparable ! Toulon, April 23 emanuele.leonora@ct.infn.it

The local response Response of each anode during the scan of the photocatode surface, with a single photoelectron pulsed beam ( spot’s diameter = 5 mm ) Used MAP: 324 local measurements with equal angular step Picture of the light source movement system to scan the photocathode Toulon, April 23 emanuele.leonora@ct.infn.it

The local response measured Area of the single photon peak for each anode. Are included events with charge more to 1/3 pe A1 A2 A4 A3 Reference system adopted Identification of the emission point from photocathode Each anode corresponds to one fourth The photocathode local response to single photoelectron for ZF0025. Color scale: in red the largest value; in blue the value less than 2 % of the largest Toulon, April 23 emanuele.leonora@ct.infn.it

The cross talk Measures of the 4 anodic signals when the center of sector 1 was illuminated with a spot Illuminated point 5 mm diam. laser intensity= 15 pe At any intensity light, in coincidence with main unipolar signal from A1, capacitive coupling between dynod chains generates bipolar parasitic signal in anodes A2, A3, A4 Parasitic signal amplitude 16 % of the main Parasitic signal charge 3% of the main Similar results were obtained illuminating the center of sectors A2, A3, A4 Pulse shape analysis in dedicated electronic board could improve the identification of the main signal Toulon, April 23 emanuele.leonora@ct.infn.it

Conclusions Two prototypes of the 4 anodes large area PMT were tested for each anode separately. The measurements present: good linearity up to 100 pe gain around 5E7 at voltage of 1550 volt similar time and charge characteristics at different anodes; only one anode (A4) presents smaller gain ( - 20 % @ 1500 V ) good identification of the emission points from photocathode presence of cross-talk: bipolar parasitic pulses with amplitudes about 16% of the main signal and a negligible charge, around 3% of the main Toulon, April 23 emanuele.leonora@ct.infn.it

… end. Thank you Toulon, April 23 emanuele.leonora@ct.infn.it

additional slides Toulon, April 23 emanuele.leonora@ct.infn.it

Typical spe pulse shape distribution Toulon, April 23 emanuele.leonora@ct.infn.it

Light Source Calibration Using a Hybrid Photo Diode (HPD) for the single-photoelectrons conditions light spectra for different laser power Using a bolometer for the range from 10 to 100 photoelectrons Toulon, April 23 emanuele.leonora@ct.infn.it

Amplitude of Cross – Talk signals is around 16 % respect to the main Amplitude of cross-talk signals (15 pe) C1 = anode1 ( trigger) ; C2 = anode2 ; C3 = anode3 ; C4 = anode 4 A1 A2 A3 A4 Amplitude of Cross – Talk signals is around 16 % respect to the main Toulon, April 23 emanuele.leonora@ct.infn.it

Negligible charge. Less than 3 % respect to main Charge of cross-talk signals (15 pe) C1 = anode1 ( trigger) ; C2 = anode2 ; C3 = anode3 ; C4 = anode 4 A1 A2 A3 A4 Negligible charge. Less than 3 % respect to main Toulon, April 23 emanuele.leonora@ct.infn.it

LabView code to control scanning Toulon, April 23 emanuele.leonora@ct.infn.it