Test Results on the Photomultiplier Tubes for the ANTARES Neutrino Telescope Juan-de-Dios Zornoza...

Test Results on the Test Results on the Photomultiplier Tubes for Photomultiplier Tubes for the ANTARES Neutrino the ANTARES Neutrino

TelescopeTelescopeJuan-de-Dios ZornozaJuan-de-Dios Zornoza

IFIC (CSIC–Valencia University, Spain)IFIC (CSIC–Valencia University, Spain)

On behalf of the ANTARES collaborationOn behalf of the ANTARES collaboration

International Workshop on UHE Neutrino TelescopesChiba, July 29-30, 2003

J. D. Zornoza - IFICJ. D. Zornoza - IFIC

ContentsContents ANTARES experimentANTARES experiment PMTs specificationsPMTs specifications Comparison of PMT candidatesComparison of PMT candidates

– Experimental setup at IFICExperimental setup at IFIC– ResultsResults– ConclusionsConclusions

Tests on the Hamamatsu R7081-20Tests on the Hamamatsu R7081-20– Experimental setup at DAPNIAExperimental setup at DAPNIA– ResultsResults– ConclusionsConclusions


ANTARES DetectorANTARES Detector The detector will consist of a 3D matrix of The detector will consist of a 3D matrix of 900 photomultipliers900 photomultipliers housed in housed in

pressure-resistant glass spheres.pressure-resistant glass spheres. These PMTs will detect the These PMTs will detect the Cherenkov lightCherenkov light emitted by the emitted by the muonmuon produced produced

in the CC interaction of the neutrino.in the CC interaction of the neutrino. The detector will be located in the The detector will be located in the MediterraneanMediterranean sea (near Toulon, France) sea (near Toulon, France)

at at 2475 m2475 m deep. deep.

350m350mactiveactive

Submarine Submarine Electro-opticalElectro-optical Cable ~40kmCable ~40km

Junction BoxJunction Box

Readout cablesReadout cables

Shore station

Shore station

anchoranchor

buoybuoy

Electronics containerElectronics container

~60m~60mCompass,Compass,tiltmetertiltmeter

Optical ModulesOptical Modules

Acoustic BeaconAcoustic Beacon

~100m

12 strings


The Optical ModuleThe Optical ModulePressure-resistant sphere

•Material: Vitrovex 8330 •Resistant to 700 bars•Inner diameter: 425 mm•Transm.: >95% (350 nm)•Good optical matching

•Material: μ metal (nickel-iron alloy)•Magnetic permeability: 5x104-1.5x105

•Magnetic field at ANTARES site: 44 μT

Magnetic Shield

Optical glue•Material: Silicone rubber gel•Optical matching glass sphere - PMT•Fixation of the mechanical position of the different elements

PMT base

•Modified version of PHQ5912 from iSeg•Compact design•Low voltage supply (±5V)•Voltage stability: 10-4

•Three last dynodes active

Internal LED•Blue LED to monitor PMT transit time•Pulse rise time: ~2 ns•Light output: 0 to 40 pJ•Stability:±5%.

The main element of the Optical Module is the PMT. The sphere also houses additional elements for operation and calibration.


Specifications (I)Specifications (I) Dimensions: the PMTs for neutrino telescopes should have a large sensitive

surface. However, the PMT has to fit in the glass sphere so the photocathode radius of curvature is limited to 19 cm (15'' PMT) and the total PMT height to 35 cm.

Gain: the amplitude of the single photoelectron (SPE peak) pulses has to be larger than 40 mV to avoid problems caused by electronic noise. This value corresponds to a gain of 5x107. In order to have a safety margin, the PMT must be able to reach a gain of 5x108.

Nominal voltage: the high voltage at which the gain is 5x107 is called nominal voltage (HVnom) and should be lower than 2000 V so as to avoid ageing problems. The specifications explained in this section are required always at the nominal voltage.

Dark noise: due to the optical background from 40K decays, the dark noise limit is not very stringent in the ANTARES experiment. This limit has been established at 25% the rate due to 40K, i.e. 15 kHz for a 10'' PMT.


Specifications (II)Specifications (II) Peak to valley ratio: in order to isolate properly the single photoelectron

signal from the pedestal, a minimum peak to valley ratio of 2 is required.

Transit time spread: transit time spread (TTS) is one of the most important parameters since a large value of the TTS could limit the angular resolution of the detector, which depends on time resolution. For this reason, a maximum of 3.6 ns (FWHM) has been established.

Pre-pulses and after-pulses: pre-pulses and after-pulses may induce misreconstructed events. The definitions and the maximum rates are in the table below. The time window is defined with respect to the expected time of the main pulse. The third column indicates if the pulse is correlated in time with a main pulse.

Type Time windowSelection

Limit

Pre-pulses [-100 ns, -10 ns] <1%

Delayed pulses [10 ns, 100 ns] <5%

After-pulses-1* [10 ns, 100 ns] <1%

After-pulses-2 [100 ns, 16 μs] <10%

*After-pulses-1 are correlated in time with a main pulse.


CandidatesCandidates Several models were studied in the pre-selection stage.Several models were studied in the pre-selection stage. Three models were considered candidates for the ANTARES Three models were considered candidates for the ANTARES

experiment (experiment (**).).

PhotomultiplierPhotocathode

diameterNumber of

stagesDynode

Structure

Hamamatsu R2018 15” 13 Venetian blind

Hamamatsu R5912-02 8” 14 Box line

Photonis XP1802 9” 11 Linear focused

ETL 9353 8” 12 Linear focused

ETL 9360KB 11” 12 Linear focused

*Hamamatsu R7081-20 10” 14 Box line

*Photonis XP1804/D2 10.6” 10 Linear focused

*Hamamatsu R8055 13” 11 Box line

Hamamatsu R7081-20 Photonis XP1804/D2 Hamamatsu R8055


Experimental Setup at IFIC (I)Experimental Setup at IFIC (I)

The PMT is inside a black box. A μ-metal cage is used in order

to shield it from the Earth magnetic field.

The laser is pulsed by means of a pulse generator and the light output is guided via an optical fiber cable inside the box.

A Lambertian diffuser is used to illuminate uniformly the photocathode.

Data acquisition is performed by CAMAC modules and the oscilloscope and sent to a PC via GPIB.

Laser

NIM Modules

Generador de pulsos

Digital Oscilloscope

CAMAC ModulesPC with Labview

Scheme of the experimental setup used at IFIC, Valencia.


Experimental Setup at IFIC (II)Experimental Setup at IFIC (II)

The laser used in the The laser used in the calibration is a Nd-YAG calibration is a Nd-YAG device. device.

It emits intense (~1It emits intense (~1μμJ) J) and short (FWHM ~ 0.8 and short (FWHM ~ 0.8 ns) pulses at ns) pulses at =532 nm =532 nm ((greengreen).).

In few minutes, a good In few minutes, a good stability is reached stability is reached (<(<3%).3%).

An internal photodiode An internal photodiode measures the emission measures the emission time with very good time with very good precision (~50 ps)precision (~50 ps)


SPE spectrumSPE spectrum The single photoelectron (SPE) charge spectrum is fitted to a The single photoelectron (SPE) charge spectrum is fitted to a

function which takes into account the different contributing terms:function which takes into account the different contributing terms:

G Gaussian distribution

P Poissonian distribution

F Valley distribution (exp + G)

μn= n·μ1 and n2= n·1

2

ω fraction of wrongly amplified electrons.

β fraction of the valley events moving to the exponential

α slope of the exponential

1

),;();(),,;(),;()(n

nnnvalleypedpedped qGnPqFqGqS

notation:notation:


GainGain

•The largest gain and the fastest increase with voltage are attained for the R7081-20 model (it has 14 dynodes).

•The model with higher nominal voltage is the R8055, since it is optimized for TTS, not for gain.

• The three models reach a gain of 108.

ModelModel HVHVnomnom (V) (V)

R7081-20R7081-20 13401340

XP1804/D2XP1804/D2 16801680

R8055R8055 19001900

Nominal voltage Nominal voltage

(Gain=5x10(Gain=5x1077))


Amplitude (SPE peak)Amplitude (SPE peak)

•The behaviour for amplitude (SPE peak) is similar to the case of gain. The highest amplitude is reached by the R7081-20.

•The value of the R8055 model at the nominal voltage is slightly low.

ModelModel Amplitude Amplitude (mV)(mV)

R7081-20R7081-20 4646

XP1804/D2XP1804/D2 6060

R8055R8055 3434

Amplitude @ HVAmplitude @ HVnomnom


Peak to ValleyPeak to Valley

•The peak to valley ratio of the R7081-20 and the XP1804/D2 at nominal voltage is around 2.7.

•The behaviour of the R8055 is very good: high P/V and quite stable around the HVnom.

ModelModel P/VP/V

R7081-20R7081-20 2.72.7

XP1804/D2XP1804/D2 2.72.7

R8055R8055 3.73.7

Peak to Valley @ HVPeak to Valley @ HVnomnom


Energy ResolutionEnergy Resolution

•The behaviour of the R7081 at low voltages is unstable, but around the HVnom is flat (~30%).

•The XP1804/D2 is also almost flat around the same value. The R8055 curve is a bit worse since it grows with voltage up to 35%.

ModelModel Energy Energy ResolutionResolution

R7081-20R7081-20 30%30%

XP1804/D2XP1804/D2 31%31%

R8055R8055 34%34%

Energy resolution @ HVEnergy resolution @ HVnomnom

*The energy resolution is defined as the ratio of the charge SPE peak width over its position.


Transit Time SpreadTransit Time Spread

• The level of illumination is around 0.3.• The threshold of discrimination is ½ photoelectron.

tpp

pt

pptf 22

1

2

1

3 exp2

exp2

1)(

0

Example of Time Distribution• The time distribution measured by the TDC is fitted to the product of a Gaussian and an exponential:

• A calibrated PMT (TTS=0.230.01 ns) is used to measure the contribution not due to the PMT

2222eleclaserPMTtot FWHMFWHMFWHMFWHM


TTSTTS

•The slope of the decrease of TTS with voltage is quite similar for the three models.

•The better value at HVnom is obtained by the XP1804/D2. All of them are within the specifications.

ModelModel TTS (ns)TTS (ns)

R7081-20R7081-20 3.03.0

XP1804/D2XP1804/D2 2.02.0

R8055R8055 2.62.6

TTS @ HVTTS @ HVnomnom


Dark Current NoiseDark Current Noise

•The lower dark noise rate of the R7081-20 can be partially attributed to its smaller surface.

•When normalizing to the same area, R7081-20 remains the better, but the other models are within the specifications.

ModelModel DC (Hz)DC (Hz)

R7081-20R7081-20 500500

XP1804/D2XP1804/D2 43004300

R8055R8055 69006900


@ HV@ HVnomnom @½ pe @½ pe


After-pulsesAfter-pulses

RateRate Pre-pulsesPre-pulses[-100 ns, -10 ns][-100 ns, -10 ns]

Delayed Delayed PulsesPulses

[10 ns, 100 ns][10 ns, 100 ns]

After-pulses-1After-pulses-1[10 ns, 100 ns][10 ns, 100 ns]

After-pulses-2After-pulses-2[100 ns, 16 [100 ns, 16 μμss]]

R7081-20R7081-20 <0.01%<0.01% 3.6%3.6% 1.0%1.0% 3.8%3.8%

XP1804/D2XP1804/D2 <0.01%<0.01% 4.7%4.7% 3.2%3.2% 18%18%

R8055R8055 2.2%2.2% 5.0%5.0% 2.4%2.4% 19%19%

•Pre-pulse rate is OK for the R7081-20 and the XP1804, but too high for R8055.

•All PMTs exhibit acceptable delayed pulse rates.

•Only R7081-20 have good values of after-pulses 1 and 2.


SummarySummary

In general, the three models are within the In general, the three models are within the specifications.specifications.

The nominal amplitude of the R8055 is The nominal amplitude of the R8055 is slightly low.slightly low.

The XP1804/D2 and the R8055 show a The XP1804/D2 and the R8055 show a high rate of after-pulses.high rate of after-pulses.

Finally, the R7081-20 was considered the Finally, the R7081-20 was considered the best choice.best choice.


Experimental Setup at DAPNIAExperimental Setup at DAPNIA After the choice of the model After the choice of the model

(R7081-20), the full sample of (R7081-20), the full sample of ANTARES PMTs (912) has been ANTARES PMTs (912) has been tested by means of an tested by means of an experimental setup capable to experimental setup capable to provide a fast way to provide a fast way to characterize them.characterize them.

This characterization was This characterization was carried out in the ‘recette’ test carried out in the ‘recette’ test bench, which consists of a light bench, which consists of a light tight plastic cylinder 1.5 m long tight plastic cylinder 1.5 m long and 0.46 m in diameter.and 0.46 m in diameter.

The PMT is illuminated by a blue The PMT is illuminated by a blue LED guided by an optical fiber.LED guided by an optical fiber.

A Lambertian diffuser is used for A Lambertian diffuser is used for uniform illumination of the uniform illumination of the whole photocathode.whole photocathode.

•All final test have been performed with an optimsed PMT base. This explains the difference between the HVnom and the TTS obtained during the final tests and the results discussed previously.


GainGain

•The mean of the distribution is ~1800 V with an RMS around 50 V.

•In all cases, the nominal voltage is below 2000 V, as required. Moreover, all the tubes reach a gain of 108.

Evolution of HVnom with the batch numberEvolution of HVnom with the batch number


Amplitude – Peak to ValleyAmplitude – Peak to Valley

•There are 20 PMTs with a low P/V value, but the mean P/V is around 2.8, i.e. within the specifications.

•There is a correlation with the batch number, which indicates a gradual improvement in this parameter.

•The mean amplitude is larger than 40 mV, which is within the recommended value.

•The amplitude of all the PMTs is larger than 35 mV.


Pulse ShapePulse Shape

Mean rise time is slightly higher than 4 ns and fall time is around Mean rise time is slightly higher than 4 ns and fall time is around 12 ns.12 ns.

Regarding time width, the value for all the PMTs is lower than 9 ns, Regarding time width, the value for all the PMTs is lower than 9 ns, i.e. acceptable according to the specifications.i.e. acceptable according to the specifications.

Rise time (ns)Rise time (ns) Time width (ns)Time width (ns)Fall time (ns)Fall time (ns)


TTSTTS•The value of TTS has been improved by a modification in the PMT base design.

•The distribution of the values of the transit time spread (FWHM) has a mean value of 2.8 ns and RMS of 0.15 ns.

•There is no tube with a TTS value larger than 3.6 ns.



•Almost all the PMTs have a dark current rate lower than 9000 Hz, i.e. within the specifications for a tube whose photocathode surface is 450 cm2.

•Only two PMTs are above this limit. Moreover, 85% of the tubes are below 3000 Hz.Threshold=1/4 pe


Pre-pulses and Delayed PulsesPre-pulses and Delayed Pulses

•The pre-pulse rate is very low (<0.1% for all the PMTs).

•Results for delayed pulses are also OK. Only two units exhibit a rate larger than 5%.


After-pulsesAfter-pulses

• The distribution of the after-pulses-1 shows two types of PMTs. Those of the first batch are above 2% and the rate for the rest is around 1.5%

•The after-pulse-2 rate is within the limits, since all PMTs show a rate below 6%.


Ageing (I)Ageing (I) Long term stability has to be checked.Long term stability has to be checked. Three PMTs were placed in a black box and excited by three Three PMTs were placed in a black box and excited by three

independent LEDs.independent LEDs. LEDs reproduced the optical background environment (LEDs reproduced the optical background environment (4040K and K and

bioluminiscence), increased by a factor two to speed up the bioluminiscence), increased by a factor two to speed up the process:process:– A continuous rate of 100 kHzA continuous rate of 100 kHz– Bursts of 1 MHz lasting 0.1 second every second.Bursts of 1 MHz lasting 0.1 second every second.


Ageing (II)Ageing (II)

Time (days)

Gain

(x1

08)

0.80.8

1.81.8

00 300300

Evolution of gain at HV constant Along the first 100 days, the Along the first 100 days, the three PMTs showed an three PMTs showed an increase of 50-70% in gain, increase of 50-70% in gain, and then stabilized (running-in and then stabilized (running-in phase).phase).

P/V, energy resolution, TTS P/V, energy resolution, TTS and dark noise remained and dark noise remained stable.stable.

After-pulse-2 rate showed an After-pulse-2 rate showed an increase (30%) most likely due increase (30%) most likely due to the accumulation of ionized to the accumulation of ionized gas atoms.gas atoms.


ConclusionsConclusions

The PMTs are a key component of the ANTARES neutrino The PMTs are a key component of the ANTARES neutrino telescope.telescope.

A list of specifications has been done in order to choose A list of specifications has been done in order to choose the optimum PMT.the optimum PMT.

After a pre-selection stage, three models were considered After a pre-selection stage, three models were considered as candidates: R7081-20, XP1804/D2 and R8055.as candidates: R7081-20, XP1804/D2 and R8055.

Taking into account these results, the R7081-20 was Taking into account these results, the R7081-20 was considered the best option.considered the best option.

A large sample of 912 units of the selected model has been A large sample of 912 units of the selected model has been tested and the results are satisfactory.tested and the results are satisfactory.

Test Results on the Photomultiplier Tubes for the ANTARES Neutrino Telescope Juan-de-Dios Zornoza...

Documents

Transcript of Test Results on the Photomultiplier Tubes for the ANTARES Neutrino Telescope Juan-de-Dios Zornoza...