The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter P R Hobson, D C Imrie, O Sharif
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Transcript of The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter P R Hobson, D C Imrie, O Sharif
HEP2001, Budapest, July 2001 R M Brown - RAL 1
The Vacuum Phototriodes for the CMS Electromagnetic Calorimeter
P R Hobson, D C Imrie, O Sharif
Brunel University, UK
K W Bell, R M Brown, D J A Cockerill, P S Flower, B W Kennedy, A L Lintern, M Sproston, J H Williams
CLRC - Rutherford Appleton Laboratory, UK
(With acknowledgements to H F Heath and colleagues at Bristol University, UK and D Seliverstov and colleagues at PNPI, Russia)
HEP2001Budapest - Hungary
July 2001
HEP2001, Budapest, July 2001 R M Brown - RAL 2
Outline of Talk Overview of CMS The Electromagnetic Calorimeter (ECAL) Properties of Lead Tungstate Radiation levels VPT Performance (End cap) APD Performance (Barrel) Status summary
HEP2001, Budapest, July 2001 R M Brown - RAL 3
Compact Muon Solenoid
Total mass : 12,500tOverall Diameter: 15.0mOverall Length: 21.6mMagnetic field: 4T
ECAL
Superconducting coil
HCAL
HEP2001, Budapest, July 2001 R M Brown - RAL 4
ECAL design objectivesBenchmark physics process:
Search for ~130 GeV Higgs via H (Sensitivity depends critically on mass resoln)
m / m = 0.5 [E1/ E1 E2
/ E2 / tan( / 2 )]
Where E / E = a / E b c/ E
Performance Aims: Barrel End cap
Stochastic term, a:(p.e. statistics/shower fluctuation)
2.7% 5.7%
Constant term, b:(non-uniformities, shower leakage)
0.55% 0.55%
Noise term, c:(Electronic noise, event pile-up)
Low L 155 MeV 205 MeV
High L 210 MeV 245 MeV
(Angular resolution limited by uncertainty in position of interaction vertex)
HEP2001, Budapest, July 2001 R M Brown - RAL 5
Lead Tungstate PropertiesAdvantages:• Fast• Dense• Radiation hard• Emission in visible
Disadvantages:• Temperature dependence• Low light yield Photodetector with gain (in a strong magnetic field)
PWO Radioluminescence Spectrum
0
5
10
15
20
340 380 420 460 500 540 580 620
Wavelength (nm)
Inte
ns
ity
Density [g/cm3] 8.28
Radn length,X0 [mm] 8.9
Interaction length [mm] 224
Molière radius [mm] 21.9
Decay time [ns] 5(39%)15(60%)100 (1%)
Refractive index 2.30
Max emission [nm] 425
Light yield [photon/MeV] ~50
Temp coeff [%/ºC] -2
HEP2001, Budapest, July 2001 R M Brown - RAL 6
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
HEP2001, Budapest, July 2001 R M Brown - RAL 7
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
HEP2001, Budapest, July 2001 R M Brown - RAL 8
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
HEP2001, Budapest, July 2001 R M Brown - RAL 9
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
HEP2001, Budapest, July 2001 R M Brown - RAL 10
VACUUM PHOTOTRIODE
HV FILTERING ELECTRONICS
CRYSTAL
‘Supercrystal’ Layout
‘Supercrystal’: carbon-fibre alveola containing 5x5 tapered crystals + VPTs + passive HV filter (160 Identical Supercrystals per Dee)
Signals fed via 600 mm cable to Preamplifier + Front End electronics behind Dee Backplate
HEP2001, Budapest, July 2001 R M Brown - RAL 11
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
500 ‘Preproduction’ VPTs delivered by RIE (St Petersburg)
HEP2001, Budapest, July 2001 R M Brown - RAL 12
Response vs Angle at B=1.8T
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-90 -60 -30 0 30 60 90VPT angle (deg.)
Rel
. An
od
e R
esp
on
se
Arrows indicate angular regions of
end caps
HEP2001, Budapest, July 2001 R M Brown - RAL 13
Typical magnetic response
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 0.5 1 1.5 2
Magnetic Field (Tesla)
Re
l. A
no
de
Re
sp
on
se
Response vs B-Field Strength
VPT Axis at 15o w.r.t. Magnetic Field
Gain Ratio (4T/0T)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
1 2 3 4 5 6 7 8 9 10 11 12 13
Relative Gain
Nu
mb
er
pe
r b
in
Batch 101-300
0.80 0.85 0.90 0.95 1.00 1.05 1.10
HEP2001, Budapest, July 2001 R M Brown - RAL 14
Distributions of Gain (B=0)
and Quantum Efficiency
0.0
5.0
10.0
15.0
20.0
15.0 17.5 20.0 22.5 25.0 27.5 30.0
Quantum Efficiency (%)
Gai
n
Batch 301-500
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Gain
Batch 301-500
Batch 101-300
6 8 10 12 14 16 18 20
Gain and quantum efficiency are uncorrelated0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Quantum Efficiency
Batch 301-500
Batch 101-300
16 18 20 22 24 26 28 30 (%)
Taken from the ‘passport’ supplied with each tube
by the manufacturer
HEP2001, Budapest, July 2001 R M Brown - RAL 15
0
5
10
15
20
25
30
35
40
45
50
1 11 21 31 41
Anode pulse height (Arb. unit)
Post-irradation
Prototypes
Batch 301-500
Batch 101-300
Batch 1-100
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
HEP2001, Budapest, July 2001 R M Brown - RAL 16
Test beam:Energy Resolution
No preshower detector With preshower detector
HEP2001, Budapest, July 2001 R M Brown - RAL 17
0
1
2
3
4
5
350 375 400 425 450 475 500 525 550 575 600 625 650 675 700Wavelength (nm)
Tran
smis
sio
n L
oss
(%
)
Sample 1
Sample 2
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)
HEP2001, Budapest, July 2001 R M Brown - RAL 18
VPT Behaviour Under Irradiation
60Co Irradiation (58 Gy/hr)
Photocurrent produced by Cerenkov light in VPT window.(Vertical lines correspond to pauses in irradiation)
0.0
5.0
10.0
15.0
0 5000 10000 15000 20000
Dose (Gy)
Ph
oto
curr
ent
(nA
)
CathodeAnode
Missing Data
VA=1000 VD= 800
HEP2001, Budapest, July 2001 R M Brown - RAL 19
VPT 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