X. -HPD Optical Module R&D for KM3NeT ( X*-HPD Optical Module R&D for KM3NeT (*Crystal-scintillator viewed by small PM) I. Al Samarai*, J. Busto*, B. Combettes*, A-G Dehaine*, D. Dornic*, F. Fouche*, G. Hallewell* *Centre de Physique des Particules de Marseille *Photonis S.A. Brive la Gaillarde Photonis - CPPM CERN Baikal VLVnT08, Toulon April 22-24, 2008

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

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 VLVnT08, Toulon April 22-24, 2008

First of all, what it ISN’T… What is the X-HPD? First of all, what it ISN’T… VLVnT08, Toulon April 22-24, 2008

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. VLVnT08, Toulon April 22-24, 2008

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) VLVnT08, Toulon April 22-24, 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). VLVnT08, Toulon April 22-24, 2008

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

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

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 Lubsandorzhiev {ex Baikal Quasar 370} interested to continue development of SMART /Quasar concept under agreement signed with Photonis (2006) on collaboration in joint photodetector development. VLVnT08, Toulon April 22-24, 2008

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 VLVnT08, Toulon April 22-24, 2008

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) VLVnT08, Toulon April 22-24, 2008

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 VLVnT08, Toulon April 22-24, 2008

8’’ Prototype with anode in form of a metal cube (1 cm3) measured at Photonis Fabrication CERN . A. Braem et al., NIM A 570 (2007) 467-474 VLVnT08, Toulon April 22-24, 2008

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 VLVnT08, Toulon April 22-24, 2008

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? VLVnT08, Toulon April 22-24, 2008

Neutrino flux predictions Kappes et al., ApJ 656:870, 2007 (astroph/0607286) 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 VLVnT08, Toulon April 22-24, 2008

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 VLVnT08, Toulon April 22-24, 2008

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) VLVnT08, Toulon April 22-24, 2008

Effective Surface Ratio: X-HPDs compared to 3 x 10” PMTs/storey VLVnT08, Toulon April 22-24, 2008

Evaluating the advantages of Spherical format X-HPDs: Volume /cost sensitivity comparison with 10” Hamamatsu R7081-20 used in ANTARES Assumptions ~350 Cherenkov photons per cm (300-600nm) 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 VLVnT08, Toulon April 22-24, 2008

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)

VLVnT08, Toulon April 22-24, 2008

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 7081-20

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 7081-20

ANTARES PM Practical diameter limit to fit in 17’’ pressure sphere Assumptions: Price of Hamamatsu 7081-20 : 995€ Sphere etc. +mechanics + electronics = 2000 € / optical module Price of 20 cm Ø p.c. X-HPD = 1.5* PM Hamamatsu 7081-20 thereafter price follows (ratio of p.c. surface area)

Photonis has built 2 prototypes of a new SMART (8”) and will supply a 3rd by summer 2008 - Internal deposition of the photocathode - Metal disk - measure of photocurrent VLVnT08, Toulon April 22-24, 2008

SIMION 8 simulations by Imen Al Samarai (CPPM) 4/08: Testing the most simple spherical X-HPD geometry R (photocathode) 95.5mm Photocathode @ 0V R(anode) 15.6mm Anode @ 25 kV No other conductive surfaces modelled TTD (North Pole–edge PC) = 0.00022ms VLVnT08, Toulon April 22-24, 2008

SIMION 8 simulations (CPPM) 4/08: Testing S8 on the Joram–C2GT X-HPD Geometry R (photocathode) 100 mm Photocathode @ -25kV Guard ring @ -26kV R(anode) 11.7mm Anode @ 0kV Grounded metal flange TTD (Equator–edge PC) = 0.0003ms VLVnT08, Toulon April 22-24, 2008

SIMION 8 simulations (CPPM) 4/08: Centred hemispheric anode on degraded glass support R (photocathode) 100 mm Photocathode @ 0 kV R(anode) 10 mm Anode @ 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 VLVnT08, Toulon April 22-24, 2008

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 VLVnT08, Toulon April 22-24, 2008

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) VLVnT08, Toulon April 22-24, 2008

Conclusion 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 VLVnT08, Toulon April 22-24, 2008