Test results from 500 preproduction VPTs R M Brown RAL - UK CERN 19 September 2001

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

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 CMS ECAL Annual Review - CERN Sept 2001 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 Selected supplier: RIE (St Petersburg) CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 3

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

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 CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 5

6. 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 Sample VPTs are measured at B =4.0T and  = 15o at Brunel Perspex diffuser plate with LEDs at corners. (Red circle indicates effective VPT diameter) 500 ‘Preproduction’ VPTs delivered by RIE in autumn 2000 CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 6

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

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

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

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

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

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

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

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

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

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

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

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 CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 18

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

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 5x1014 fast n cm-2 Require complete absence of internal discharge at 1000V, at 0T and 1T  B  4T CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 20

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 CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 21