development of hpds for applications in physics and medical...
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Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 1
Development of Development of HPDsHPDs
for applications for applications
in physics and medical imagingin physics and medical imaging
A. Braem, E. Chesi, Christian Joram, J. Séguinot, P. WeilhammerCERN / PH
representing the CIMA collaboration and the C2GT team
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 2
OutlineOutline
Why Hybrid Photo Detectors ?
Some Developments for physics experiments5-inch 10-inchA spherical HPD for neutrino detection
A flat HPD for 3D-Axial PET scanner
www.cern.ch/ssd/HPD
Great support by our technical staff: F. Cossey, C. David, I. Mcgill, M. v. Stenis, …
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 3
Hybrid Photon Detectors (HPD)Hybrid Photon Detectors (HPD)
∆V
photocathode
focusing electrodes
siliconsensor+ FEelectronics
e-
light quantum
segmentedsiliconsensor
Combination of sensitivity of PMT with excellent spatial and energy resolution of silicon sensor
Gain:
Gain is achieved in a single dissipative step !
eV6.3CUeG ⋅
≈ UC = 20 kV → G ~ 5000
small compared to σelectronics
GFG ⋅≈σ
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 4
Classical HPD designsClassical HPD designs
• Proximity focused• 1:1 imaging• Operates in axial
magnetic fields.
• ‘Fountain’ focused• Demagnification D• No real focusing→ ballistic point spread
• Intolerant to magnetic fields
• ‘Cross’ focused• Demagnification D• Focusing leads to
small point spread• Intolerant to magnetic
fields
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 5
Main advantages of HPD technologyMain advantages of HPD technology• Excellent signal definition• Allows for photon counting• Free choice of segmentation (50 µm - 10 mm)• Uniform sensitivity and gain• no dead zones between pixels
2 p.e.
Drawbacks• Rel. low gain (3000 - 8000) → low noise
electronics required• Expressed sensitivity to magnetic fields
CMS HCAL, 19-pixel HPD (DEP, NL)
Pad HPD
Single padS/N up to 20
1 p.e.
2 p.e.
3 p.e.
Viking VA3 chip (τpeak = 1.3 µs, 300 e- ENC)UC = -26 kV
elec
troni
c no
ise
cut
pulse height (ADC counts)
• e- backscattering from Si surface continuous ‘background’εdet (p.e.) ~ 85-95 %
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 6
Some prototype developments for physics experimentsSome prototype developments for physics experimentsdeveloped and built at CERN
NIM A 442 (2000) 128-135
NIM A 478 (2002) 400-403
www.cern.ch/ssd/HPD
5-inch 10-inch
127 mm Ø, D ~ 2.5,2048 channels 1mm2
bialkali photocathode
254 mm Ø, D ~ 4,2048 channels 1mm2
bialkali photocathode
NIM A 504 (2003) 19
NIM A 518 (2004) 574-578
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 7
νe, νµ, ντ
CC reactionsin H2O
segmented photosensitive ‘wall’about 250 × 250 m2
Fiducial detectorvolume ~ 1.5 Mt
(Eν below threshold for τ production)
~ 50 m
e±, µ± 42°Che
renko
v ligh
t
Cherenkov light
Principle of neutrino detection by Cherenkov effectin C2GT (CERN To Gulf of Taranto)
The wall is made of ~600 mechanical modules (10 x 10 m2), each carrying 49 optical modules.
10 m
A. Ball et al., C2GT, Memorandum, CERN-SPSC-2004-025, SPSC-M-723
A. Ball et al., Proc. of the RICH2004 conference, subm. to NIM A
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 8
The ideal photodetector for C2GTThe ideal photodetector for C2GT
• large size (>10”) • spherical shape, must fit in a pressure sphere• ± 120° angle of acceptance• optimized QE for 300 < λ < 600 nm• single photon sensitive• timing resolution 1-2 ns• no spatial resolution required• electronics included • cost-effective (need ~32.000 !)• adapted to industrial fabrication
120°
42°
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 9
432 mm
(17”)380 mm
PAHV
optical gel(refr. index matching + insulation)
benthos sphere(432 / 404)
electrical feed-throughsvalve
standard base plate of HPD 10” (prel. version).
C2GT Optical Module
15
joint Si sensor
ceramic support
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 10
ElectrostaticsElectrostatics
Simulations Simulations with SIMION 3Dwith SIMION 3D
110º
-150 -100 -50distance from centre (mm)
-15000
-10000
-5000
0
5000
10000
15000
Φ (V
) or
E (V
/cm
)
Φ ~ 1/r
E ~ 1/r2 • Potential and field distribution similar to
a point charge.
• Low field at photocathode (~100 V/cm),
• Very high field close to Si sensor (~10,000 V/cm). Try to reduce by a grounded field cage around Si sensor.
120º
- 20.3 kV
- 20 kV
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 11
0 20 40 60 80 100 1209
10
11
12
Tran
sit t
ime
(ns)
polar angle (deg.)
0 < φ< 120°
Transit TimeTransit Time
9.0 9.5 10.0 10.5 11.0 11.5 12.0Transit Time (ns)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
rel.
frequ
ency
(a.u
.)
σ = 0.15 nsRMS = 0.18 ns
angles > 110°
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 12
A A ‘‘halfhalf--scalescale’’ prototypeprototype208 mm (~8-inch)
Al coating2 rings
Development in collaboration with Photonis-DEP, C. Fontaine et al.
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 13
Current status: All main components ready ‘dry assembly’
First tests will be done with a metal cube rather than Si sensors
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 14
Development for Development for HPDsHPDs for medical imaging for medical imaging The 3D axial PET cameraThe 3D axial PET camera
Axial arrangement of camera modules based on matrices of long crystals read out on both sides by HPDsPreprint CERN PH-EP/2004-050, submitted to NIM A
§ Patent filed. No. WO2004008177 §
HPD2
HPD1
x
y
Principleof a cameramodule
z
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 15
Technical realization
208 crystals (YAP)
3.2 × 3.2 ×100 mm3
gap between crystals 0.8
mm
HPD • proximity focused• ceramic body• sapphire window• bialkali PC
2 VATA-GP5 ASIC
Si sensor 2 x 104 pads (4 x 4 mm2)
ceramic PCB (4 layers)
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 16
VATA-GP5 (CERN – IDE AS co-development, www.ideas.no)
fast shaper
mask
ORdiscr.
VFP FORTrigger
tresh.
Det.
S/H
slowshaper
AnalogOut
150 ns
25 ns
preamp
• VATA-GP5, 128 ch./chip• Auto-triggering analog front-end• serial and sparse readout• time walk compensation• 0.6 µm CMOS
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 17
15 20 25 30 35 40 45 50Vbias (volt)
0
30
60
90
120
sign
al (A
DC
cou
nts)
VATA-GP5 ASIC + ceramic PCB + Si-sensor operational
Si Sensor Depletion(UPC = -15 kV)
5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.50
50
100
150
200
250
sign
al (A
DC
cou
nts)
- UC (kV)0 500 1000 1500 2000 2500
0
50
100
150
200
250
300
350
Qin (fC)
sign
al (A
DC
bin
)sparse readout
serial readoutcut-off at 6 kV(too thick n+ layer)
CaF2
photo-electrons
UV lightsource
CsI
DAQ
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 18
2 sealed protoype tubes produced so far… both were not perfect
50 60 70 80 90xmir (mm)
4
6
8
10
12
14
charge vs spot position(centre of gravity)
m = 1.04
centre sensorx d
et (p
ads)
PC109• 50 mm Ø Si-sensor• VA-prime electronics• bialkali cathode (22%)• HV problem
PC113• PET Si-sensor• VATA-GP5
electronics• bialkali cathode• electronics suffered
due to accident during processing
0
4
8
12
16
20
24
Q.E
. (%
)
Photocathode 109 "PCR5" sealedCenter of cathode
250 350 450 550 650
lambda (nm)
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 19
Summary and OutlookSummary and Outlook
Our team is developing …
a flat HPD with auto-triggering electronics, aimed at medical imaging applications, in particular PET with single crystal readout.
Sealed fully operational prototype imminent (days!)
a spherical HPD for underwater Cherenkov detector for neutrino physics.
Sealed prototype later this year.
After finally having entered HEP at large scale (CMS, LHCb), HPDs may also have a bright future in some advanced applications(niches?) in other
fields.
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 20
BACK-UP slides
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 21
0.45 Gauss
B
E~1/r2 produces a focusing effect
effect of earth magentic field seems
to be marginal
Effect of angular spread and magnetic fieldEffect of angular spread and magnetic field• Ekin(t0) = 2 eV (conservative)
• -40º ≤ θem ≤ 40º (rel. to surface)
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 22
Is EIs E--field around field around SiSi sensor too high ?sensor too high ?A grounded grid could help
Grid at ‘natural’ potential: -11 kV
-11.000 V
0 V
~23
mm
500 V/mm
1000 V/mm1500 V/mm
2000 V/mm
Gradients up to 2000 V/mm at edges of Sisensor
Grid at 0 V
0 V
0 V
Gradients at Si sensor reduced to ~500 V/mm. High field around grid, f(diam.).
500 V/mm
500 V/mm
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 23
Fabrication
Large number of tubes needed industrial fabrication internal process (as for large PMTs).
However, this would lead to a ‘pollution’ of Si-sensor and high field region with Cs/K/Sb.protect by mask (difficult!)use ‘hybrid’ process ?
Q.E. monitoring
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 24
Processing in the existing set-up at CERN, used for 5” and 10” HPDs
10ӯ
Only minor mechanical adaptations required.
5ӯ
heating element
glass envelope Sb source
K/Cs sources
base plate with pre-mounted sensor
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 25
0 40 80 120 160input charge (fC)
60
70
80
90
100
110
time
wal
k (n
s)
Gain 0Gain 1
+/- 5 ns
Beaune 2005 C. Joram CERN / PH Development of HPDs for applications in physics and medical imaging 26
vacuum pump (turbo)P < 10-5 mbar
DAQReadout
card
CaF2
Si sensor (300 µm)208 pads (4×4 mm2)
VME
UV H2 flash lamp(self triggering)
CsI photctahode (300 nm)Deposited on a grid(Au, 80% transparency)
MgF2
MgF2
collimator
mirror
mask (at ground)photo-electrons
Experimental set-up for VATA-GP5 tests with photo-electrons
-UPC = 15-20 kV