1. X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008
X*-HPD Optical Module R&D (*Crystal-scintillator viewed by small PM) I. Al Samarai, J. Busto, D. Dornic, G. Hallewell Centre de Physique des Particules de Marseille
Photonis
CERN
Baikal
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

2. From… Presentation by B
From… Presentation by B. Combettes (Photonis) NNN07, Hamamatsu, Japan, October 2007

3. X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008
Presentation
What is the X-HPD?
History of the X-HPD;
X-HPD advantages – why develop it?
Who are the actors?
Present status inc R&D at CPPM;
Future developments
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

4. First of all, what it ISN’T…
What is the X-HPD?
First of all, what it ISN’T…
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

5. It isn’t like the LHC-b HPD (DEP Photonis) shown here…
80mm
The X-HPD :
is big, like a hemispherical PM;
has standard bi-alkali p.c. and borosilicate window;
has no electronics in the vacuum volume;
is compatible with internal photocathode processing like PM;
is insensitive to the Earth’s magnetic field;
(photoelectrons accelerated in ~25kV)
120mm
Under vacuum, the X-HPD contains (only…) :
glass,
chemical products + evaporators for the photocathode,
scintilating crystal, encapsulated in aluminium,
electrodes, pins and wires,
getters, as necessary.
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

6. What is the X-HPD? A “simple” detector of single
photons with a bialkali p.c.
High accelerating field (~25kV) between p.c. & scintillating crystal (short Tdecay) under thin metallic layer (Al, 100nm)
Preferably a completely
spherical geometry, with
scintillator at the centre
Efficiencies for electrostatic collect.+ conv.p.c. improved
 Global Efficaciency ~33% (compare to ~16% PM hemi)
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

7. X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008
The first crystal-HPD: Philips SMART : Phosphor P47 (YSO:Ce) ~30 manufactured (1980s-1992)
History of the X-HPD
G. van Aller et al.
A "smart" 35cm Diameter Photomultiplier. Helvetia Physica Acta, 59, 1119 , (1986).
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

8. Baikal Quasar-370 (1983) Hybrid (X-HPD) -Hemispherical dome =370 mm
-Photocathode K2CsSb
-Preamplification 25 kV
Scintillator
Y2SiO5 (TTS= 2ns FWHM)
Traditional PMT
K2CsSb 13-stages =25 mm
gprimary ~ 35, st ~ 2.5 ns / Npe
1 photoelectron on main photocathode  20…30 photoelectrons on small PM

9. 200 tubes in operation since 1996
BAIKAL
Quasars in operation since 1993:
200 since 1998
R. Bagduev et al., Nucl. Instr. Meth. A 420 (1999) 138

10. The Actors: (Last meeting at RICH2007, Trieste, Oct 07)
Photonis (B. Combettes, F. Fouche, A-G. Dehaine
INFN Genova (Mauro Taiuti, D. Bersani)
CERN (Christian Joram, Jacques Seguinot; collaboration between CERN - Photonis)
CPPM (Imen Al Samarai, Greg Hallewell, Jose Busto;
collaboration via GIS IN2P3-Photonis)
INR Moscow
(Bayarto Lubsandorshiev {ex Baikal Quasar 370}
very interested to continue development
of the SMART/Quasar concept)
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

11. SMART & Quasar were the first X-HPD tubes
But scintillator in the form of disk didn’t fully exploit the potential…
Preferable to use a 3-D or ‘volume’ scintillator at the exact geometric
centre of a spherical envelope (iso-chronicity + global efficaciency
{(# photoelectrons seen)/ (# photons arriving)} )
PMT
XP2982
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

12. Toward Development of a large spherical X-HPD hybrid photodetector
CERN - Photonis:
Toward Development of a large
spherical X-HPD hybrid photodetector
Braem +, C. Joram +, J. Séguinot +, L. Pierre *, P. Lavoute *
+ CERN, Geneva (CH) * Photonis SAS, Brive (F)
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

13. Advantages of a spherical tube with anode at geometric centre
Radial electric field
s TTS negligeable
Efficiency of electrostatic collection
~100% over ~ 3p Sr
Mu-metal screen unnecessary
Large detection solide angle (dW ~ 3p)
Gain in effective QE sensitivity by ‘Double-
passage’ effect through photocathode
To be compared with : ~ 70% over only 4p/3 Sr
in a hemispherical PM!
Nesessary for a hemispheric PM
T ~ 0.4
X2 compared to a hemispheric PM QE QE
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

14. 8’’ Prototype with anode in form of a metal cube (1 cm3) ‘Proto 0’
measured at Photonis
Fabrication CERN .
A. Braem et al., NIM A 570 (2007) 
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

15. Optical module in pressure sphere for KM3NeT?
380 mm
± 120° acceptance
Sensitive to single photons
Time resolution 1-2 ns FWHM
Q.E. optimised 300 < l < 600 nm
dark counts <0.1 per 100 ns
Pressure Sphere
17”(432 / 404) 15
Scintillating
Crystal
Si sensor
432 mm
(17”)
joint
Light
Guide
Glass
Support
ceramic support
Optical gel
(matching ind. ref.
+ isolation)
Small PM HV PA
Inox base plate
electrical feed-throughs
valve
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

16. The advantages of X–HPDs in spherical geometry: Why develop them?
Significant uncertainties in the rate
of n production at E > ~1016eV ; n telescopes at ~ km3 scale {like ICE CUBE & KM3NeT} big enough?
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

17. Neutrino flux predictions
Kappes et al.,
ApJ 656:870, 2007
(astroph/ )
mean atm. flux (Volkova, 1980, Sov.J. Nucl.Phys., 31(6), 784
Estimated neutrino flux – in reach for KM3NeT
All calculations show that we need multi-km3 detectors
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

18. Neutrino effective area estimation
Damien Dornic, CPPM
HPDs with 40%
overall detection
(instead of 23%
for standard PMs)
efficiency flat over 3p
3 X-HPDs in place of 3 standard PMs (orientation - 45°)
2 X-HPDs horizontal
“Peanut” geometry
(opposing direction), each storey rotated 90° w.r.t. previous)
Base configuration: hexagon of 127 lines (~0.35 km3)
 separated by 85m. Each line 34 storeys spaced at 15m
ANTARES site parameters
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

19. Angular resolution comparison
HPDs with 40%
overall detection
(instead of 23%
for standard PMs)
efficiency flat over 3p
3 X-HPDs in place of 3 standard PMs (orientation - 45°)
2 X-HPDs horizontal
“Peanut” geometry
(opposing direction), each storey rotated 90° w.r.t. previous)
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

20. Effective Surface Ratio: X-HPDs compared to 3 x 10” PMTs/storey
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

21. Evaluating the advantages of Spherical format X-HPDs:
Volume /cost sensitivity comparison with 10” Hamamatsu R used in ANTARES
Assumptions
~350 Cherenkov photons per cm ( nm)
Attenuation length 35m (combined absorption, scattering)
Photon flight 40m/sinqC (qC = 43°) =56m
Cost per ANTARES OM =
PM: 995€, electronics: 600€, mechanics: 660€, sphere+other 600€
Cost per X-HPD OM
1.5* cost of ANTARES tube of same diameter
+electronics 600€ + sphere etc. 600€ + mechanics 660€
therafter scaled as ratio of areas for different diameters
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

22. ANTARES PM Assumptions:
- Attenuation length in sea water: 35m
- Trajectory of muon ~ 40m from PMs (average)
~ 350 Cherenkov photons produced per cm (300<l<600nm)

23. X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

24. ANTARES PM Price of Hamamatsu 7081-20 : 995€ Assumptions:
Sphere etc. +mechanics + electronics = 2000 € / optical module
Price of 20 cm Ø p.c. X-HPD = 1.5* PM Hamamatsu

25. ANTARES PM Price of Hamamatsu 7081-20 : 995€ Assumptions:
Sphere etc. +mechanics + electronics = 2000 € / optical module
Price of 20 cm Ø p.c. X-HPD = 1.5* PM Hamamatsu

26. ANTARES PM Practical diameter limit to fit in 17’’ pressure sphere
Assumptions:
Price of Hamamatsu : 995€
Sphere etc. +mechanics + electronics = 2000 € / optical module
Price of 20 cm Ø p.c. X-HPD = 1.5* PM Hamamatsu
thereafter price follows (ratio of p.c. surface area)

27. X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008
Photonis has built 2 prototypes of a new SMART (8”) and will supply a 3rd by summer Internal deposition of the photocathode - Metal disk - measure of photocurrent
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

28. SIMION 8 simulations by Imen Al Samarai (CPPM) 4/08:
Testing the most simple spherical X-HPD geometry
R (photocathode) 95.5mm 0V
R(anode) 15.6mm
25 kV
No other conductive
surfaces modelled
TTD (North Pole–edge PC)
= ms
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

29. SIMION 8 simulations (CPPM) 4/08:
Testing S8 on the Joram–C2GT X-HPD Geometry
R (photocathode) 100 mm
-25kV
Guard -26kV
R(anode) 11.7mm
0kV
Grounded metal flange
TTD (Equator–edge PC)
= ms
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

30. SIMION 8 simulations (CPPM) 4/08:
Centred hemispheric anode on degraded glass support
R (photocathode) 100 mm
0 kV
R(anode) 10 mm
25kV
20 mm diam.
60mm high glass support
With degrader to 0V
on outside
(simulated conductive paint
used in latest Joram prototype)
No other conductive
surfaces modelled
TTD North Pole – Equator
0.0003ms

31. SIMION 8 simulations by Christian Joram April 2008
X-HPD OM R&D KM3NeT OM meeting Genova, April 9-11, 2008

32. Near future developments
Photonis have identified the technique for p.c. deposition as critical to cost – progress in ‘internal deposition’
CERN-Photonis will test the 8” pure spherical geometry
X-HPD with LYSO crystal (for NDIP2008, June 2008)
Parallel crystal studies (CERN-Photonis, IPN Orsay)
At CPPM, measurements of TT, sTT, HT behaviour, l-integrated photocurrent, multi-g res…
(Photonis funding of stage + these PhD)
Mid 2008: Fabrication & test of prototype 8” tubes with metal anode
End 2008: Fabrication & test of 8” HPD tubes
with crystal anodes in different configurations
End 2009: Fabrication and test of prototype 15” X-HPD
with best crystal anode

33. Some Longer term developments
Progress from 8’’ prototypes to larger, up to original 15’’ of Flyckt/Val Aller SMART?
(Photocathode deposition  internal or quasi-internal processing: Cost/unit driven lower than hemispherical PM of same Ø?)
In parallel, tests of an 8” prototype in a sphere at ANTARES/NEMO/NESTOR
(need to pass to ‘weaponisation’ phase: compatibility with power & r/o system)
Development from Baikal 24V25kV DC-DC supply:
Low power Cockroft-Walton multiplier: reliability issues,
Can we build from designs of TV tube HV supplies (compatibility of reqt?)
(huge statistical MTBF sample + Photonis-Philips connection)
These above issues to be addressed in WP3/ANR context
 We welcome new collaborators, ideas to this effort !

34. Conclusion  Cost savings: larger water volume instrumented
Pure spherical geometry X-HPDs based on Flyckt/Van Aller
Philips SMART tube could be very promising Čg – detectors for underwater n telescopes
~100% photoelectron collection eff. (over 3p Sr) (& sTT<1ns )
(c.f. 65% over ~ 4p/3 cathode surface area in ‘hemispherical’ PM)
Much larger photocathode area than same Ø hemispherical PM
+ suppression of m-metal cage
Improved Q.E. (transmissive  reflective) over large % of 3p
 enhanced overall detection effiency
Improved multi-g sensitivity with small PM readout, possible directionality for segmented PC + multi-anode PM
 Cost savings: larger water volume instrumented
with a given number of photon detectors