1. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 1 Test results from 500 preproduction VPTs R M Brown RAL - UK CERN 19 September 2001

2. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 2 Outline of talk VPT Operation Supercrystal layout Test facilities at RAL and Brunel Characterisation results: Angle scan B-field response Gain Photocathode sensitivity Radiation hardness Photocathode uniformity Technical specification Summary

3. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 3 Photodetectors: end caps B-field orientation favourable for VPTs (Axes: 8.5 o < | | < 25.5 o wrt to field) More radiation hard than Si diodes (with UV glass window) Gain 8 -10 at B = 4 T Active area of ~ 280 mm 2 /crystal Q.E. ~ 20% at 420 nm = 26.5 mm MESH ANODE Vacuum Phototriode (VPT): Single stage photomultiplier tube with fine metal grid anode Selected supplier: RIE (St Petersburg)

4. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 4 VPT Gain vs Dynode Voltage

5. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 5 VACUUM PHOTOTRIODE HV FILTERING ELECTRONICS CRYSTAL Supercrystal Layout Supercrystal: carbon-fibre alveola containing 5x5 tapered crystals + VPTs + passive HV filter (138 Identical Supercrystals per Dee) Signals fed via 600 mm cable to Preamplifier + Front End electronics behind Dee Backplate

6. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 6 Characterisation of VPTs 4.0T Solenoid at Brunel1.8T 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 -30 o 30 o at RAL Sample VPTs are measured at B =4.0T and = 15 o at Brunel 500 Preproduction VPTs delivered by RIE in autumn 2000

7. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 7 Response vs Angle at B=1.8T Arrows indicate angular regions of end caps

8. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 8 Response vs B-Field Strength VPT Axis at 15 o w.r.t. Magnetic Field 0.80 0.85 0.90 0.95 1.00 1.05 1.10

9. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 9 Distributions of Gain (B=0) and Quantum Efficiency 6 8 10 12 14 16 18 20 Gain and quantum efficiency are uncorrelated 16 18 20 22 24 26 28 30 (%) Taken from the passport supplied with each tube by the manufacturer

10. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 10 0 10 20 30 40 50 60 70 80 90 100 Anode Response Distribution B=1.8T =15 o Spread in anode response Some sorting of VPTs necessary

11. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 11 Test beam:Energy Resolution No preshower detector With preshower detector

12. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 12 Faceplate optical transmission Post-irradiation Loss in optical transmission of 2 faceplate samples after 25 kGy 60 Co irradiation (380Gy/hour) (approx 10 yrs LHC at = 2.6)

13. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 13 VPT Behaviour Under Irradiation 60 Co Irradiation (58 Gy/hr) Photocurrent produced by Cerenkov light in VPT window. (Vertical lines correspond to pauses in irradiation) V A =1000 V D = 800

14. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 14 Photocathode Uniformity VPT operated as a diode Blue LED ( = 430 nm, 0.5mm spot)

15. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 15 Cathode uniformity - VPT 137

16. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 16 Cathode uniformity - VPT 354

17. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 17 e - beam vs LED measurement

18. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 18 B-field sensitivity (H2 vs RAL) Relative response of prototype 1 VPTs: RAL B=1.8T vs H2 B=3.0T Relative response, B=3.0T/B=0T, H2

19. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 19 Technical Specification for Pre-production VPTs

20. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 20 Technical Specification for Production VPTs Burn-in less severe (4hrs @ 100nA vs 10hrs @ 200nA), Burn-in ratio tightened from 0.8 t0 0.9 Lower limit on P and G reduced, but previously defined before burn-in Lower limit on product PxG effectively increased There is now an upper limit on PxG to limit spread in anode response Sample faceplates must transmit 90% of PWO light after 20kGy and 5x10 14 fast n cm -2 Require complete absence of internal discharge at 1000V, at 0T and 1T B 4T

21. CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 21 Summary A new generation of fine-mesh VPTs has been developed to satisfy the high magnetic field/radiation hardness requirements of CMS An automated characterisation facility has been commissioned to handle 15000 devices The performance of 500 pre-production VPTs from RIE meets CMS requirements Some sorting by anode sensitivity will be necessary The technical specification has been revised The full production order for 15000 devices is about to be placed