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Performance Characteristics of Production VPTs

R M Brown, B W Kennedy, P R Hobson

(with crucial input from D J A Cockerill, M Raymond, C Seez)(and thanks to M Sproston, A L Lintern, J H Williams and

K W Bell for the RAL Measurements)

4 December 2002

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Outline of Talk Delivery status Test Status Specification Test set-up Test Results Radiation levels Face plate irradiation VPT Performance Anomalous behaviour Conclusions

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Photodetectors: end caps

•B-field orientation favourable for VPTs (Axes: 8.5o < || < 25.5o wrt to field)

•More radiation hard than Si diodes (with UV glass window)

• Gain 8 -10 at B = 4 T

• Active area of ~ 280 mm2/crystal

• Q.E. ~ 20% at 420 nm

= 26.5 mm

MESH ANODE

Vacuum Phototriode (VPT):

Single stage photomultiplier tube with fine metal grid anode (10 m pitch)

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VPT Gain vs Dynode Voltage

0

2

4

6

8

10

12

0 200 400 600 800 1000

Dynode Voltage

Gai

n

V(A)=1000V

V(A)=800V

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Technical specification

Response in a magnetic field:

There shall be a complete absence of internal discharge at normal operating voltage, in zero field, and for magnetic fields between 1 and 4T, at angles in the range 0o to 26o to the VPT axis.

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Delivery Status

0

2000

4000

6000

8000

10000

12000

14000

16000

# VPT

Date

VPT production

Planning 500 1000 1600 2300 3300 4300 5300 6300 7300 8400 9500 10500 11500 12600 13700 14800 15500

Delivered 500 1200 1900 2600 3200

Q1 2001

Q2 2001

Q3 2001

Q4 2001

Q1 2002

Q2 2002

Q3 2002

Q4 2002

Q1 2003

Q2 2003

Q3 2003

Q4 2003

Q1 2004

Q2 2004

Q3 2004

Q4 2004

Q1 2005

Q2 2005

Q3 2005

Q4 2005

%

18%21%

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Characterisation of VPTs

4.0T Solenoid at Brunel 1.8T Dipole Magnet at RAL

Detail of RAL test Cell

Perspex diffuser plate with LEDs at corners. (Red circle indicates effective VPT diameter)

All VPTs are measured at 0 B 1.8T and -30o 30o at RALSample VPTs are measured at B =4.0T and = 15o at Brunel

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Acceptance testing status

Ordered 500+15000 = 15500

Delivered 500+2700 = 3200

Visual inspection 500+2700 = 3200

Tested up to 1.8T 500+2200 = 2700

Tested at 4T 100+165 = 265

Faceplate irradiations 17 batches (36 faceplates)

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Delivery and testing vs time

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Determining the grid orientation

The result of the ‘’ scan depends on the ‘’ orientation of the grid. (Not fixed in prodn)

is determined during visual inspection. (Laser interference pattern)

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Anode response vs angle (1.8T)

Arrows indicate angular range covered by EE

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Anode response vs magnetic field

B =15o

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Anode sensitivity

86% have18< A< 40 e/MeV

A

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Normalisation of RAL Test Set-up

2002 2001 Difference

18.7 18.9 -1.0%

20.3 20.1 +1.4%

19.9 19.8 +1.0%

15.9 16.1 +0.8%

18.8 22.8 -20.9%

Estimated yield (e/MeV)For 5 prototype RIE tubes

‘Absolute yield’ estimatedfrom 1999 test beam run in H4

using prototype VPTs from ET, Hamamatsu and RIE.

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RAL/RIE Correlation

Anode sensitivity (RAL) (pulsed, B=1.8T)

versus

Photocathode-efficiency x Gain (RIE)

(dc, B=0T)

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Relative gain at 4T

Production tubes

0

10

20

30

40

50

60

70

0.8 0.85 0.9 0.95 1 1.05 1.1 >1.1

Relative 4T/0T pulsed gain (upper bin edge)

Nu

mb

er

in b

in

Passed

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Doses and neutron fluences

Integrated dose (kGy) and neutron fluence (x1013 cm-2) for L = 5x105 pb-1 (~10 yrs)

Black: Dose in the Crystals at the position of the shower maximumBlue: Dose behind the crystals at the position of the photodetectorsRed: Neutron fluences behind the crystals

0.20.350.5

3

2050

1.22

5

70

HCAL Barrel

ECAL Barrel

ECAL Endcap

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Faceplate irradiationYC-49 Batch 31226b

20.8 kGy dose

-0.02

0

0.02

0.04

0.06

0.08

0.1

300 400 500 600 700 800

Wavelength (nm)

Ind

uc

ed

ab

so

rba

nc

e

91.4% transmission of PbWO4 spectrum after 20.8 kGy

Radiation Hardness: Sample faceplates shall, neglecting surface reflection losses,

transmit at least 90% of PbWO4 light, following a dose of 20 kGy and exposure to a

fluence of 5x1014 fast neutrons cm-2.

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CMS ECAL Layout

3170 mm

1290 mm

Parameter Barrel End caps

Xtal size (mm3)Depth in X0

21.8 × 21.8 × 23025.8

30.0 × 30.0 × 22024.7

No. crystalsVolume (m3)Xtal mass (t)

612008.1467.4

146642.7722.9

Full projective geometry

(‘Off-pointing’ by ~3o)

Barrel: 17x2 Crystal types

End cap: 1 Crystal type

14648

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Transverse Noise

Analysis by Chris Seez et al:

‘Transverse noise’ ETnoise = Enoise x sin

Allows for light loss in PWO (dose vs ),etc

Exploits variation in VPT response to achieve uniform ET

noise after ‘sorting’

But assumes Response A 34 e/MeV

(28 e/MeV more realistic)

Coverage27%

29%

19%

12%

11%

2%

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Possible noise improvements for endcapif reduce dynamic range requirement to 1500 GeV

Cpf -> Cpf/2, Rpf -> 2.Rpfcharge amp. gain doubled and subsequent noise sources less significant

Gain RG Diff. stage gain

Energy range [GeV]

Noise [electrons]

Energy range [GeV]

Noise [electrons]

32 20 8 0 – 94 3166 0 – 47 2409

8 20 2 94 – 375 3351 47 - 188 2517

4 40 2 375 - 750 3934 188 – 375 2785

1 80 1 750 – 3000 7478 375 – 1500 4694

3 TeV fullscale

1.5 TeV fullscale

Noise simulation of ‘MGPA’(From talk by Mark Raymond)

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Anomalous behaviour at 1.8T

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Response vs time

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Anomalous behaviour at 4T

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Summary VPT Production is well underway (>20% delivered on schedule)

RAL capacity for testing at 1.8T is adequate and allows for some re-testing if required

Batch VPT testing at 4T and faceplate irradiation checks progressing smoothly at Brunel

The measured performance of the VPTs matches the EE design objectives, but ‘sorting’ will be required to accommodate the spread in anode response

Anomalous behaviour has been observed in some tubes at certain angles in a high magnetic field. This is under investigation by RIE