pad hpd proposal 3 nov 1999 c. joram the pad hpd as photodetector of the lhcb rich detectors ...
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Pad HPD Proposal 3 Nov 1999 C. JoramTRANSCRIPT
Pad HPD Proposal 3 Nov 1999 C. Joram
The Pad HPD
as Photodetectorof the
LHCb RICH Detectors
General Design L0 Electronics R&D: Results + Future Tube Fabrication + costs
C. Joram
for the
Pad HPD team
Pad HPD Proposal 3 Nov 1999 C. Joram
Granularity ca. 2.5 mm
High filling factor Single photon sensitivity
Robust operationCost effectiveness
LHCb RICH Requirements
Large area High sensitivity for E<5.5 eV
LHC speed readout
Pad HPD Proposal 3 Nov 1999 C. Joram
Pad HPD Proposal 3 Nov 1999 C. Joram
The Design of the Pad HPD Total (active) diameter: 127 (114) mm
69% filling factor when hex. closed pack + 3mm gap space for mu-metal + insulation
Bialkali photocathode + UV extended borosilicate window good compromise between E and
chrom.
Fountain shaped electron optics purely linear adjustable demagnification strong E-field over full tube robustness against magnetic fields
Work at maximum high voltage (25 kV) large signal (ca. 6000-6500 e-) low point spread function (pixel error) robustness against magnetic fields
Round Si sensor with pads of 1 x 1 mm2
no dead space, no unused pads pixel error matches other error sources
E
n
Pad HPD Proposal 3 Nov 1999 C. Joram
Analog readout electronics full exploitation of information continuous online pedestal determination + subtraction can cope with common mode + other noise sources
Tube design allows to re-use all components
Tube can be manufactured by LHCb RICH group or by industry
Pad HPD Proposal 3 Nov 1999 C. Joram
Summary of the Pad HPD characteristics
General:
total diameter 127 mm (5")active diameter 114 mmgranularity at entrance window 2.3 x 2.3 mm2
entrance window type UV-extended borosilicate glassentrance window transmission T=50% at ca. 250 nm, T=0 at ca. 200 nmphotocathode bialkali K2CsSb, semitransparentquantum efficiency > 20% at 390 nm
Electrostatics:
electrodes 4 concentric ring electrodesfocusing fountain typedemagnification 2.3, constant over full active diameter
Silicon sensor:
Si sensor diameter 50 mm active diameterSi sensor thickness 300 m (160 m will be tested, which will result in a
faster charge collection)segmentation 2048 pads of 1 x 1 mm2, no dead spaceE-loss in dead layer (n+ + Al) ca. 1 keV
Readout electronics:
Level-0 readout Analog readout scheme. 16 SCTA128 chips, inside tubeSCTA128 features comply with LHCb specifications (25 ns peaking time, 4s L0 latency, 32 fold multiplexing)Operation:
max. cathode voltage -25 kVsignal 6600 e- (expected)pedestal noise 650 e- (expected)S/N ratio 10 (expected)single el. det. efficiency 92.8%, 4 sigma cut (expected)
Mounting:
Tube arrangement Hexagonal close packingTotal number of tubes 216gap between tubes 3 mm (allowing for -metal shielding)active area fraction 69%
Pad HPD Proposal 3 Nov 1999 C. Joram
L0 Electronics of the Pad HPD
SCTA128 modified according to LHCb specifications. SCTA128_LHCb Analog readout chip in rad hard DMILL technology. Chip is fully identical with proposed vtx chip.
preamp shaperanalog pipeline
4 x
32 fo
ld a
nalo
g m
ultip
lexi
ng
silicon diode
128 channels
derand.buffer
diffe
rent
ial a
nalo
g ou
t
SCTA128 exists and has demonstrated peaking time 25 ns analog multiplexing at 40 MHz expected noise figures: 398 + 55 pF-1
For the Pad HPD (ca. 4 pF) we expect a pedestal noise of 650e- ENC S/N = 10 det. = 92.8% (4 cut)
Necessary LHCb modifications will be discussed under future R&D
Pad HPD Proposal 3 Nov 1999 C. Joram
R&D programme of the Pad HPD
1996 1997 1998 1999 2000
Concept, design, fabrication of HPD components
Test of electron optics, Si sensor, VA electronics (CsI PC)
Design, fabrication, commissioning of HPD plant
Development of tube processing (PC, sealing, getter)
Further optimization of processing. Final electronics.
Main Results of the R&D
Difficulties and problems
Future R&D
Pad HPD Proposal 3 Nov 1999 C. Joram
Main Results of the R&D
0
3
6
9
12
15
18
21
24
27
Q.E
. (%
)
Photocathode 59Center of cathodeNon-uniformity <10%
300 350 400 450 500 550 600 650
wavelength (nm)
4.00
3.69
3.39
3.39
3.09
2.83
2.50
2.24
2.09
1.99
energy (eV)
47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
cathode no.
0
2
4
6
8
10
12
14
16
18
20
22
24
Q.E
. (%
) at 4
00 n
m
Q.E. of a good HPD
Summary ofall cathodesproduced sinceMarch 1999
Quantum efficiency of bialkali cathodes
Pad HPD Proposal 3 Nov 1999 C. Joram
Comparison of lab. measured Q.E. and test beam data
PC59 tested with 180 cm long C4F10 radiator
• Expect 48 p.e.• Find 54 p.e. (noise subtracted)
• Agreement withinuncertainties
Online displayof single eventring
-30
-20
-10
-0
10
20
30
x silic
on (m
m)
m = 2.7
114 mm
0.00 31.75 63.50 95.25 127.00
xcathode (mm)
Electron Optics of the Pad HPD
• 114 mm active
• Linear demagnification,• adjustable
• Fit residuals 200 m
Pad HPD Proposal 3 Nov 1999 C. Joram
Electron optics with mu-metal shield
-25
-20
-15
-10
-5
0
x silic
on (m
m)
m = 2.2
57 mm
60.0 77.5 95.0 112.5 130.0
xcathode (mm)
160
mm
63.5
mm
110
mm
128 mm, 0.9 mm thick
Linear opticsnot affected by grounded shield.
Pad HPD Proposal 3 Nov 1999 C. Joram
Point spread function
measured on Si plane
14 15 16 17 18 19 20 21 22 23 24 25Cathode Voltage (kV)
200
250
300
350
400
450
500
Poi
nt S
prea
d F
unct
ion
(m
)
Pixel Error
Pad HPD Proposal 3 Nov 1999 C. Joram
Measurement in B-field (Helmholtz coil)
11 12 13 14 15 16 17 18 19 20 21
UC (kV)
15
20
25
30
/B
(mra
d/G
auss
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
R
/R/B
(%/G
auss
)
Axial B-field, no shield
0 5 10 15 20 25
Baxial (Gauss)
0
10
20
30
40
50
60
(mra
d) a
t UC =
16
kV
Axial B-field, 160 mm long mu-metal shield
/B = 2.2 mrad / GaussR/R negligible
pad granularity: 1 mm = 40 mrad
Axial B-field, no shield
Axial B-field, with shield
Pad HPD Proposal 3 Nov 1999 C. Joram
-1 1 3 5 7 9 11 13 15 17 19
By (Gauss)
-1
0
1
2
3
4
x-sh
ift (m
m) a
t UC =
14
kV
Transverse B-field (in y direction)
with and without 160 mm long mu-metal shield
x = 32 m/Gauss
x = 0.39 mm/Gauss
• A 160 mm long mu-metal shield is very effective forBE : reduction of by factor 12, R/R0BE: reduction of x by factor 12
• For reasonably low fields (B<10 Gauss) the shift and the rotation becomes negligible
• A short shield (110 mm) has been tested but found to be less efficient (only factor 3 reduction)
• If a long shield has to be used, a pointing geometry is possible (12% fewer tubes required)
measured on Si-plane
x
y
B
Transverse B-field,
For reasonably low fields (B<10 Gauss) the shift and the rotation become negligible
pointing geometry
16 6
Pad HPD Proposal 3 Nov 1999 C. Joram
0 2 4 6 8 10 12 14 16 18 20 22voltage (kV)
0
10
20
30
40
50
60
70
80
90
pulse
hei
ght o
f 1st
pho
toel
ectro
n (A
DC
bin
s)
0.53 kV
num
ber o
f e/h
pai
rs
1000
2000
3000
4000
5000
6000
Pedestal cut (4)
Single pad
S/N = 20
1 p.e.
2 p.e.
3 p.e.
Viking VA3 chip (peak = 1.3 s, 300 e- ENC)UC = -26 kV
ADC counts
Signals on the Si sensor
thanks to a thinned n+ and Al layer
Pad HPD Proposal 3 Nov 1999 C. Joram
Exposure to direct charged particles
•Data at 0º and 25º incidence angle
•Photons from C-effect in window well localized 20-40 multi photon hits.
•Charged particles in Si sensor easily identifiable
•Results in agreement with Malcolm’s simulations.
•Analog information useful for event cleaning.
C-photonsfrom windowx = x 1.2 mm
Signals fromcharged particlesx 1.3 mmY 2.2 mm
Pad HPD Proposal 3 Nov 1999 C. Joram
Difficulties and ProblemsPhototube fabrication is not extremely difficult, but...
we started essentially from zero many parameters have to be precisely tuned difficult diagnostics of ambiguous symptoms only few trials
Two problems caused significant delays Some envelopes develop leaks during bakeout
Problem understood and fixedby SVT. A good fraction of our
envelopes are affected.However: All tubes can be repaired!
Some tubes with bialkali cathodedo not stand full cathode voltage
Problem understood but not fully fixed.K and Cs atoms adhere to impurities on glass surface. Surface conductivity Field distortions
atomic excitation under HV light emission
Improved (chemical) cleaning helps !Walls can be protected by mask. To be tested.
Pad HPD Proposal 3 Nov 1999 C. Joram
Future R&D
Further optimization and stabilization of theof tube fabrication process
Build tubes with final LHCb electronics
Modification of SCTA analog frontend
• FE identical to existing ABCD chip
• expect 650 e- noise in Pad HPD
• submission still in 1999
Modifications of SCTA backend
• 4 s pipeline• 432 multiplexing• reduced set-up time
• submission by 2/2000
Pad HPD Proposal 3 Nov 1999 C. Joram
ID Task Name1 Complete tests w ith VA electronic
2 Bakeout test of exist. SCTA128
3 Vacuum test of exist. SCTA128
4 Process SCTA128 w ith mod. FE
5 Process SCTA128 w ith mod. BE
6 Fabricate sealed HPD w ith exist SCTA
7 Fabricate sealed HPD w ith f inal SCTA
28/2
30/6
Oct Nov Dec Jan Feb Mar Apr May Jun Jul AugQtr 4, 1999 Qtr 1, 2000 Qtr 2, 2000 Qtr 3, 2000
In the meantime…
demonstrate vacuum operation of existing SCTA128HC
demonstrate baking of SCTA128HC
Finally…
produce sealed HPD with existing SCTA128HC produce sealed HPD with final SCTA128_LHCb
R&D finished by mid 2000 !
Pad HPD Proposal 3 Nov 1999 C. Joram
Tube Fabrication
We considered 3 possible fabrication scenarios
A) In-house production at CERN (baseline of proposal)
B) Distributed in-house production (CERN + other institutes inside LHCb)
c) Industrial fabrication: 1 offer available (Thomson, France), a 2nd offer in preparation (Photek, UK)
Pad HPD Proposal 3 Nov 1999 C. Joram
ID Task Name1 SCTA128 w ith mod. FE/BE available
2 Reserve for possible 2nd SCT iteration
3 Purchasing of HPD components
4 Design of fabrication plants
5 Fabrication/commissioning of plants
6 Photodetector fabrication/tests
7 All Photodectors available/tested
1/5
1/
H1 H2 H1 H2 H1 H2 H1 H2 H1 H22000 2001 2002 2003 2004
Our baseline scenario
240 Pad HPDs are required to be ready and testedby mid 2004. 2 new optimized fabrication plants have to be built (re-using existing special components) 4 Pad HPDs are produced per week 240 tubes can be produced in 22 months
assuming average yield of 80% 40 production weeks/yr
HPD fabrication should start by beginning of 2002
There is sufficient time to • design, build and commission plants• re-iterate on SCTA128 if required
All technical labour is included in cost estimate !
Pad HPD Proposal 3 Nov 1999 C. Joram
Cost estimate
(Details will be given by Dave Websdale.)
Total cost of 216 tubes (incl. encapsulated electronics)
A) In-house: 2.0 MCHF (ca. 30% labour)
B) Distr. in-house: unknown, could be less than A)
C) Industry: 3.2 MCHF
Pad HPD Proposal 3 Nov 1999 C. Joram
Conclusion The Pad HPD is a photodetector which has
been coherently designed to fulfill the LHCb RICH requirements in an optimum way.
The achieved performance and the expected results of the remaining R&D phase make it an excellent candidate.
The (distributed) in-house fabrication represents a cost-effective scenario, which allows to produce all tubes well in time and still provides sufficient reserves.
Many thanks to
all members of the Pad HPD team,
our industrial partners,and all people who generously supported us.