CMS Week, CERN, 2002 R M Brown - RAL 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 and K W Bell for the RAL Measurements) 4 December 2002

CMS Week, CERN, 2002 R M Brown - RAL 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 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 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 (10  m pitch)

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

CMS Week, CERN, 2002 R M Brown - RAL 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 0 o to 26 o to the VPT axis.

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

CMS Week, CERN, 2002 R M Brown - RAL 7 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

CMS Week, CERN, 2002 R M Brown - RAL 8 Acceptance testing status Ordered = Delivered = 3200 Visual inspection = 3200 Tested up to 1.8T = 2700 Tested at 4T = 265 Faceplate irradiations17 batches (36 faceplates)

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

CMS Week, CERN, 2002 R M Brown - RAL 10 Determining the grid orientation The result of the ‘  ’ scan depends on the ‘  ’ orientation of the grid. (Not fixed in prod n )   is determined during visual inspection. (Laser interference pattern)

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

CMS Week, CERN, 2002 R M Brown - RAL 12 Anode response vs magnetic field  B =15 o

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

CMS Week, CERN, 2002 R M Brown - RAL 14 Normalisation of RAL Test Set-up Difference % % % % % Estimated yield (e/MeV) For 5 prototype RIE tubes ‘Absolute yield’ estimated from 1999 test beam run in H4 using prototype VPTs from ET, Hamamatsu and RIE.

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

CMS Week, CERN, 2002 R M Brown - RAL 17 Doses and neutron fluences Integrated dose (kGy) and neutron fluence (x10 13 cm -2 ) for  L = 5x10 5 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 HCAL Barrel ECAL Barrel ECAL Endcap

CMS Week, CERN, 2002 R M Brown - RAL 18 Faceplate irradiation 91.4% transmission of PbWO 4 spectrum after 20.8 kGy Radiation Hardness: Sample faceplates shall, neglecting surface reflection losses, transmit at least 90% of PbWO 4 light, following a dose of 20 kGy and exposure to a fluence of 5x10 14 fast neutrons cm -2.

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

CMS Week, CERN, 2002 R M Brown - RAL 20 Transverse Noise Analysis by Chris Seez et al: ‘Transverse noise’ E T noise = E noise x sin  Allows for light loss in PWO (dose vs  ),etc Exploits variation in VPT response to achieve uniform E T noise after ‘sorting’ But assumes Response A  34 e/MeV (28 e/MeV more realistic) Coverage 27% 29% 19% 12% 11% 2%

CMS Week, CERN, 2002 R M Brown - RAL 21 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 GainRGRG Diff. stage gain Energy range [GeV] Noise [electrons] Energy range [GeV] Noise [electrons] – – – – – – TeV fullscale1.5 TeV fullscale Noise simulation of ‘MGPA’ (From talk by Mark Raymond)

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

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

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

CMS Week, CERN, 2002 R M Brown - RAL 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