1. 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, 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

2. 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

3. 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

4. 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 V for ZF about 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

5. 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

6. 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

7. Definition of Secondary Pulses
According to Hamamatsu
Toulon, April 23

8. 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

9. 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

10. 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

11. 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

12. 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 ( 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

13. … end.
Thank you
Toulon, April 23

14. additional slides
Toulon, April 23

15. Typical spe pulse shape distribution
Toulon, April 23

16. 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

17. 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

18. 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

19. LabView code to control scanning
Toulon, April 23