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
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.
Mar 28, 2015
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CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 1
Test results from 500 preproduction VPTs
R M BrownRAL - UK
CERN19 September 2001
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 3
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
Selected supplier:RIE (St Petersburg)
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 4
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
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 6
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 in autumn 2000
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 7
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 8
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 9
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 10
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 11
Test beam:Energy Resolution
No preshower detector With preshower detector
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 12
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)
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 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)
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 14
Photocathode Uniformity
88 first measurement
0
20
40
60
80
100
120
140
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43
measurements
curr
ent
in n
A
VPT operated as a diode
Blue LED ( = 430 nm, 0.5mm spot)
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 15
Cathode uniformity - VPT 137
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 16
Cathode uniformity - VPT 354
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 17
e- beam vs LED measurement
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
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 19
Technical Specification for Pre-production VPTs
Quantity Meaning RangeP Photocathode quantum
efficiency at 420nm18%
G Current gain at zero field 8B Burn-in ratio 0.8R (Response at
4T)/ (Response at 0T) 0.75
Q Q = PGBR 1.15F Excess noise factor < 4.0ia
max Maximum anode currentfrom 0 - 4T
2 nA
Length Overall length of VPT 46mmStublength
Length of seal-off stub 14mm
Diameter External diameter ofinsulating sleeve
26.3-26.5mm
Table 1. Technical specification of VPTs. Measurements are to bemade with anode and dynode voltages of 1000V and 800Vrespectively relative to the photocathode, using a blue LED of430nm wavelength.
CMS ECAL Annual Review - CERN Sept 2001 R M Brown - RAL 20
Technical Specification for Production VPTs
Revised Technical Specification
Quantity Meaning Range
P Photocathode quantum efficiency at 420 nm 15%
G Current gain at zero B-field 7
PxG Indicative of anode response at zero B-field 1.4 PxG 3.8
R Response at 4T/Response at 0T 0.75
B Burn-in ratio (4 hours @ IPC=100nA): IA(f)/IA(I) 0.9
Ia
max
Maximum anode dark current at zero B-field(at 1100V, after 10 minutes at 1200V)
2nA
F Excess noise factor at 4T and 15O 4.5
DAngular dependence of anode response at 4Tover the range 8O 26O, relative to 15O
10%
HLoss of anode response after 20kGy and5x1014 fast neutrons cm-2
10%
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 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
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