Development of Hybrid Photon Detectors for a Novel Deep Sea Neutrino Experiment

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


CCERNNNeutrinosto GGran SSasso

-Under construction

-Beam in 2007

Reminder:Reminder:

CNGS

Reminder:Reminder:

CNGS


Gulf of Taranto

C2GTC2GTContinuation of CNGS beam to Gulf of Taranto (Ionian Sea)

Deep trench allows to perform neutrino experimentsin a depth > 1000 m


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


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.


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°


‘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.


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


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°


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)


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


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


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


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


-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


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


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


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


208 mm (~8-inch)

A ‘half-scale’ A ‘half-scale’ prototypeprototype

Al coating2 rings


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


Enevlope under fabrication at SVT, France.

Sphere blown from a glass cylinder !

Expect 3 envelopes with flange before end ’04.


Processing in the existing set-up at CERN, used for 5” and 10” HPDs

10”Ø

Only minor mechanical adaptations required.

5”Ø

heating element

glass envelope Sb source

K/Cs sources

base plate with pre-mounted sensor


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.


Back-up stuff …


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)


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


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


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%


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


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)


-20 kV

0 kVOptics / HV not optimized ?

Timing looks ok. < 1 ns TTS

‘out’

Hamamatsu 13” prototype

Development of Hybrid Photon Detectors for a Novel Deep Sea Neutrino Experiment

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