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C. Joram RICH 2004 Mexico November 2004
Development of Hybrid Photon Detectors
for a Novel Deep Sea Neutrino Experiment Development of Hybrid Photon Detectors
for a Novel Deep Sea Neutrino Experiment • C2GT to measure Neutrino Oscillations
• The Photodetector - requirements- design considerations
• Concept of a spherical HPD- electrostatics- signal characteristics- fabrication issues
• A half scale prototype
A.E. Ball, A. Braem, L. Camilleri, A. Catinaccio, G. Chelkov, F. Dydak, A. Elagin, P. Frandsen, A. Grant, M. Gostkin, A. Guskov, C. Joram, Z. Krumshteyn, H. Postema, M. Price, T. Rovelli, D.
Schinzel, J. Seguinot, G. Valenti, R. Voss, J. Wotschack, A. Zhemchugov
C. Joram RICH 2004 Mexico November 2004
CCERNNNeutrinosto GGran SSasso
-Under construction
-Beam in 2007
Reminder:Reminder:
CNGS
Reminder:Reminder:
CNGS
C. Joram RICH 2004 Mexico November 2004
Gulf of Taranto
C2GTC2GTContinuation of CNGS beam to Gulf of Taranto (Ionian Sea)
Deep trench allows to perform neutrino experimentsin a depth > 1000 m
C. Joram RICH 2004 Mexico November 2004
C2GT – what and why ?C2GT – what and why ?
The concept of C2GT consists of a planar Cherenkov underwater detector, operated at a depth of ~1000m, and at a baseline around 1200 km. The detector can be displaced to assess baselines from 1100 – 1700 km.
The CNGS neutrino beam could be converted with modest effort (no civil engineering!) to a quasi-monoenergetic off-axis neutrino beam, delivering of E = 0.8 GeV to the gulf of Taranto (radial distance from CNGS Beam axis: 44 km)
Under certain (reasonable) assumptions, neutrino oscillations at large distances can be described by only 3 parameters:
The experiment allows to measure all 3 !
E
LmvvP
2232
232
134 27.1
sin2sincos)(
223m
13213
22323 ,, mm
( 13 is small cos413 ~ 1 )
Assuming ~ 2.5×10-3eV2 (Super-K), a 0.8 GeV beam would have its first and second oscillation maximum at L = 400 and L = 1200 km.
A scan at 3 different baselines (1+1+5 yrs) leads to a precision in sin223 of 8% and in of 1%.
223m
C. Joram RICH 2004 Mexico November 2004
Nature seems to prefer bimaximal mixing, i.e |23| ~ |12| ~ 45°
E
LmvvP e
2232
132
232 27.1
sinsinsin)(
132sin2)( evvP
At the previously established baseline with maximum oscillation, the e probability becomes
C2GT could establish a non-zero value of sin213 with a 3 discovery potential for a value of 0.0039 or could improve the current upper limit of sin213 < 0.05 by about a factor 30.
C. Joram RICH 2004 Mexico November 2004
Principle of neutrino Principle of neutrino detection by detection by Cherenkov effectCherenkov effectin C2GTin C2GT
e, ,
CC reactionsin H2O
segmented photosensitive ‘wall’about 250 × 250 m2
(E below threshold for production)
Fiducial detector volume ~ 1.5 Mt
~ 50 m
Chere
nkov
light
Light absorption length in sea water
Cherenkov light
e±, ± 42°
C. Joram RICH 2004 Mexico November 2004
‘muon event’ ‘electron event’
Use ‘amplitude’ information and fuzziness to distinguish between muon and electron events. The method require a certain granularity of the photosensor plane.
M.C. predicts muon misidentification of 1×10-3 at 90% electron efficiency.
C. Joram RICH 2004 Mexico November 2004
The detector - basic ideas:The detector - basic ideas:
The detector plane, fixed at the sea bed. A mechanical module (~10 x 10 m) with 49 photosensors
C. Joram RICH 2004 Mexico November 2004
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 < < 600 nm• single photon sensitive• timing resolution 1-2 ns • dark counts <0.1 per 100 ns • no spatial resolution required• electronics included • cost-effective (need ~32.000 !)• adapted to industrial fabrication
120°
42°
C. Joram RICH 2004 Mexico November 2004
Design considerations Silicon or dynodes ?Silicon or dynodes ?
silicon dynodesAngular coverage > ± 90° Angular coverage < ± 60°
TTS < 1 ns (FWHM) ? TTS ~ 3 ns
det (1 p.e.) ~93% (back scattering) det (1 p.e.) ~90%
‘delicate’ components (Si, ceramics) only metal inside tube
no magnetic shielding needed (to be verified !)
mu-metal shielding needed
Unifrom response over ± 90° Uniform response over ± 25°
If silicon, p-i-n diode or APD ?p-i-n diode or APD ?
p-i-n APD
Signal at 20 kV: 5·103 e, G = 1 2-3 ·105 e, G ~ 50
Cd = 35 pF/cm2 , ENF ~ 1 Cd = 300 - 1500 pF/cm2, ENF = 2 - 5
detector size arbitrary few sizes available (1,3,5 mm Ø, 5x5 mm2)
C. Joram RICH 2004 Mexico November 2004
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 C2GT PhotodetectorPhotodetector
15
joint Si sensor
ceramic support
C. Joram RICH 2004 Mexico November 2004
ElectrostaticsElectrostatics 110º
-150 -100 -50distance from centre (mm)
-15000
-10000
-5000
0
5000
10000
15000
(V
) or
E (V
/cm
)
~ 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).
Too high ?
- 20 kV
120º
- 20.3 kV
C. Joram RICH 2004 Mexico November 2004
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.
freq
uenc
y (a
.u.)
= 0.15 nsRMS = 0.18 ns
angles > 110°
0 20 40 60 80 100 1209
10
11
12
Tra
nsit
time
(ns)
polar angle (deg.)
0 < < 120°
Transit TimeTransit Time
C. Joram RICH 2004 Mexico November 2004
Effect of angular spread and magnetic fieldEffect of angular spread and magnetic field
• Ekin(t0) = 2 eV (conservative)
• -40º em 40º (rel. to surface)
0.45 Gauss
B
E~1/r2 produces a focusing effect
effect of earth magentic field seems
to be marginal
C. Joram RICH 2004 Mexico November 2004
-11.000 V
0 V
~23
mm
500 V/mm
1000 V/mm
1500 V/mm
2000 V/mm
Is E-field around Si sensor too high ?Is E-field around Si sensor too high ?
A grounded grid could help
Grid at ‘natural’ potential: -11 kV
0 V
0 V
Gradients up to 2000 V/mm at edges of Si sensor
Grid at 0 V
Gradients at Si sensor reduced to ~500 V/mm. High field around grid, f(diam.).
500 V/mm
500 V/mm
C. Joram RICH 2004 Mexico November 2004
Signal CharacteristicsSignal Characteristics
Signal amplitude• UC = 20 kV signal 1 p.e. ~ 5000 e-
Design of Si sensors• 15 x 15 mm2, mini guard ring, aim for > 90% active area
Electronics• fast (peak = 100 ns) and low noise (500 e-) - impossible to reach for CD = 70-80 pF segment sensor (e.g. 4 fold)
Timing characteristics• Need t ~ 2 ns for single photons• Requires most likely waveform digitization
Electronics + readout need much more work !
Problem ?• Electronics reads signal over a 20 cm long distance
C. Joram RICH 2004 Mexico November 2004
Big thank you to Alan Rudge and Peter Weilhammer
2 cm readout wire 20 cm readout wire
Si 300 m thickCD = 36 pF
0.0 0.5 1.0 1.5 2.00
200
400
600
800
= 2.12 keV
~ 590 e- RMS
Silver x-ray22.1 / 24.9 keV
Co 60gamma59.5 keV
energy (ADC counts)
even
ts
0.0 0.5 1.0 1.5 2.00
400
800
1200
Silver x-ray22.1 / 24.9 keV
even
ts
energy (ADC counts)
Co 60gamma59.5 keV
= 2.21 keV
~ 614 e- RMS
2 or 20 cm wire (non-coax)
cm
s = 2 s s = 2 s
Ortec 450
InterFETJ310
+Vb
241Am 241Am
C. Joram RICH 2004 Mexico November 2004
Fabrication 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
C. Joram RICH 2004 Mexico November 2004
208 mm (~8-inch)
A ‘half-scale’ A ‘half-scale’ prototypeprototype
Al coating2 rings
C. Joram RICH 2004 Mexico November 2004
standard 5” baseplate
Si sensors5 pieces12 x 13.2 mm2
in a grounded field cage
‘‘artistic view’artistic view’of the half-scale of the half-scale prototypeprototype
C. Joram RICH 2004 Mexico November 2004
Enevlope under fabrication at SVT, France.
Sphere blown from a glass cylinder !
Expect 3 envelopes with flange before end ’04.
C. Joram RICH 2004 Mexico November 2004
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
C. Joram RICH 2004 Mexico November 2004
Summary and conclusions
C2GT is a conceptual study of an experiment to precisely measure 13
A spherical HPD has been designed which promises to meet the C2GT requirements
Strong features• Large acceptance• Low TTS• Good signal definition
Critical issues• Low noise and short peaking time for large detector capacitance • Industrialization of production
A half scale propotype tube is under construction to prove the basic characteristics of this design.
If successful, the prototype could be used to for deep sea site exploration studies.
C. Joram RICH 2004 Mexico November 2004
Back-up stuff …
C. Joram RICH 2004 Mexico November 2004
0 250 500 750 1000 1250 1500 1750 2000shaping time (ns)
0
500
1000
1500
RM
S n
oise
(e- )
Si diode 36 pF
Variation of shaping time of Ortec 450
fit = 1/sqrt(s)
C. Joram RICH 2004 Mexico November 2004
17.00
5.00
9.00
R 190.00
R 185.00
R 216.00
R 207.00
angle sphere
angle detector
n_sph = 1.472 sphere refr. index n_win = 1.47 window refr. index n_gel = 1.404 optical gel: refr. index n_wat = 1.345 water refr. index
Calculations take into account- refraction (3D) at all interfaces- Fresnel reflection/transmission as f()- bulk absorption
45º
_sph = 300 mm absorption length_win = 500 mm “_gel = 600 mm “
Full Detector Geometry
-40 -20 0 20 40 60 80 100 120 140theta_sphere (deg.)
-80
-52
-24
4
32
60
88
116
144
172
thet
a_de
tect
or (
deg.
)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
tran
smis
sion
pro
babi
lity
30º 45º
60º
45º30º
60º
C. Joram RICH 2004 Mexico November 2004
10.00
4.00
Ø 200.00
Ø 208.00
R 159.00
R 168.00
9.00
theta_sphere
theta_window
45.00
Prototype Detector Geometry
45º
-30 -10 10 30 50 70 90theta_sphere (deg.)
-60
-40
-20
0
20
40
60
80
100
120
140
160
thet
a_de
tect
or (
deg.
)
0.0
0.2
0.4
0.6
0.8
1.0
tran
smis
sion
pro
babi
lity
60º45º
30º
60º
30º45º
C. Joram RICH 2004 Mexico November 2004
Dark count rate
Rough estimate
/se102.2A105.3
1000
2774
/103.8
????5.1
)/exp(
221
2
5
2
J
cmA
KCT
KeVk
eVW
kTWATJ
th
th
Looks too optimistic. Varies strongly with Wth.
Literature (Philips PM handbook)Tambient: Rdark = 10-1000 Hz/cm2
Expect to gain a factor 5-10 by coolingT4C: Rdark = 1 - 200 Hz/cm2
R4C,total(4000cm2) = 4·103 - 8·105 Hz
Prob for 1 single photon hit in 20 s = 8% - 1600%
Prob for 1 single photon hit in 100 ns = 0.04% - 8%
C. Joram RICH 2004 Mexico November 2004
Basic considerations (3)
Fabrication process:
Internal external
faster turn-around time long bake + pump cycle
cheap equipment expensive equipment
tube sealed before processing, just pumping and source ports sealed after.
in-situ sealing (indium ?)
bakes all components at 300 deg.C selective baking T
pollute tube and Si-sensor with K/Cs masks protect tube + and Si sensor
C. Joram RICH 2004 Mexico November 2004
332.00
120.00
105.00
192.00
92.00
64.00
68.00
The Hamamatsu13” prototype
(from A. Kusuka, Master thesis, U. Tokyo, Feb 2004)
C. Joram RICH 2004 Mexico November 2004
-20 kV
0 kVOptics / HV not optimized ?
Timing looks ok. < 1 ns TTS
‘out’
Hamamatsu 13” prototype
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