Performance Characteristics of Production VPTs R M Brown, B W Kennedy, P R Hobson

1. 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 andK W Bell for the RAL Measurements) 4 December 2002 CMS Week, CERN, 2002 R M Brown - RAL 1

2. Outline of Talk • Delivery status • Test Status • Specification • Test set-up • Test Results • Radiation levels • Face plate irradiation • VPT Performance • Anomalous behaviour • Conclusions CMS Week, CERN, 2002 R M Brown - RAL 2

3. =26.5 mm MESH ANODE 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 • Vacuum Phototriode (VPT): • Single stage photomultiplier tube with fine metal gridanode (10mm pitch) CMS Week, CERN, 2002 R M Brown - RAL 3

4. VPT Gain vs Dynode Voltage CMS Week, CERN, 2002 R M Brown - RAL 4

5. 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. CMS Week, CERN, 2002 R M Brown - RAL 5

6. Delivery Status 21% CMS Week, CERN, 2002 R M Brown - RAL 6

7. Characterisation of VPTs Detail of RAL test Cell 4.0T Solenoid at Brunel 1.8T Dipole Magnet at RAL All VPTs are measured at 0  B  1.8T and -30o 30o at RAL Perspex diffuser plate with LEDs at corners. (Red circle indicates effective VPT diameter) Sample VPTs are measured at B =4.0T and  = 15o at Brunel CMS Week, CERN, 2002 R M Brown - RAL 7

8. Acceptance testing status CMS Week, CERN, 2002 R M Brown - RAL 8

9. Delivery and testing vs time CMS Week, CERN, 2002 R M Brown - RAL 9

10. 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) CMS Week, CERN, 2002 R M Brown - RAL 10

11. Anode response vs angle (1.8T) Arrows indicate angular range covered by EE CMS Week, CERN, 2002 R M Brown - RAL 11

12. Anoderesponsevsmagneticfield B =15o CMS Week, CERN, 2002 R M Brown - RAL 12

13. Anode sensitivity 86% have 18< A< 40e/MeV A CMS Week, CERN, 2002 R M Brown - RAL 13

14. Normalisation ofRAL Test Set-up 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. CMS Week, CERN, 2002 R M Brown - RAL 14

15. RAL/RIE Correlation Anode sensitivity (RAL) (pulsed, B=1.8T) versus Photocathode-efficiency x Gain (RIE) (dc, B=0T) CMS Week, CERN, 2002 R M Brown - RAL 15

16. Relative gain at 4T CMS Week, CERN, 2002 R M Brown - RAL 16

17. HCAL Barrel ECAL Endcap 0.2 1.2 0.35 0.5 2 ECAL Barrel 5 3 70 20 50 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 maximum Blue: Dose behind the crystals at the position of the photodetectors Red: Neutron fluences behind the crystals CMS Week, CERN, 2002 R M Brown - RAL 17

18. Faceplate irradiation 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. CMS Week, CERN, 2002 R M Brown - RAL 18

19. CMS ECAL Layout Full projective geometry (‘Off-pointing’ by ~3o) Barrel: 17x2 Crystal types End cap: 1 Crystal type 1290 mm 3170 mm 14648 CMS Week, CERN, 2002 R M Brown - RAL 19

20. Transverse Noise Analysis by Chris Seez et al: ‘Transverse noise’ ETnoise = Enoisex sin Allows for light loss in PWO (dose vs ),etc Exploits variation in VPT response to achieve uniform ETnoise after ‘sorting’ But assumes Response A  34e/MeV (28e/MeV more realistic) CMS Week, CERN, 2002 R M Brown - RAL 20

21. Noise simulation of ‘MGPA’(From talk by Mark Raymond) 3 TeV fullscale 1.5 TeV fullscale Possible noise improvements for endcap if reduce dynamic range requirement to 1500 GeV Cpf -> Cpf/2, Rpf -> 2.Rpf charge amp. gain doubled and subsequent noise sources less significant CMS Week, CERN, 2002 R M Brown - RAL 21

22. Anomalous behaviour at 1.8T CMS Week, CERN, 2002 R M Brown - RAL 22

23. Response vs time CMS Week, CERN, 2002 R M Brown - RAL 23

24. Anomalous behaviour at 4T CMS Week, CERN, 2002 R M Brown - RAL 24

25. 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 CMS Week, CERN, 2002 R M Brown - RAL 25