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 Building upon the experience of the Philips (Photonis) ‘Smart’ Tube (Flyckt – Van Aller) The Baikal Quasar370 of NT-200 and the spherical X-HPD R&D at CERN (Joram et al) SMART Photonis – CPPM 2008 prototype Baikal CERN Our R&D carried out under the GIS (Groupement d’interet Scientifique) contract between CNRS-IN2P3 and Photonis Our Aim: to increase the Cherenkov Photon Horizon in sea water through the electrostatic and Quantum efficiency enhancements offered by X-HPDs, and to minimize X-HPD unit cost - to increase the volume of water instrumentable in a neutrino telescope of a given budget KM3NeT WP3 meeting Oct 15, 2008

From… Presentation by B From… Presentation by B. Combettes (Photonis) Identified as a major Photonis priority for n detectors NNN07, Hamamatsu, Japan, October 2007 Reiterated at NNN08, APC, September 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 KM3NeT WP3 meeting Oct 15, 2008

First of all, what it ISN’T… What is the X-HPD? First of all, what it ISN’T… KM3NeT WP3 meeting Oct 15, 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. It is SIMPLE and already proven -200 in operation at Lake Baikal KM3NeT WP3 meeting Oct 15, 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 Eff. for electrostatic collect.+ (Standard Bialkali) Q.E Global Efficiency ≥33% (40% av.~50% max)  (cf ~16% hemispherical PM) KM3NeT WP3 meeting Oct 15, 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). KM3NeT WP3 meeting Oct 15, 2008

Quasi-internal photocathode deposition (NOT A TRANSFER PROCESS)…! 8 grains of Sb (deposition of PC) P47 (YSO:Ce) phosphor Deposited on glass Sb deposition shield (+25kV) Domed +25kV surface Quasi-internal photocathode deposition (NOT A TRANSFER PROCESS)…! KM3NeT WP3 meeting Oct 15, 2008

Internal details of SMART 15” (from Photonis Archives) Electrodes + feedthroughs for antimony evaporation Antimony screen (limits solid angle of p.c.deposition) +25kV * * Ports for connections to in-tube evaporators for K, Cs 0V 0V Photonis Stargate Meeting 12/9/2007 KM3NeT WP3 meeting Oct 15, 2008

The Philips SMART Tube The QUASAR 370 Tube pressure sphere R. Bagduev et al., Nucl. Instr. Meth. A 420 (1999) 138 PMT XP2982 G. van Aller et al. A "smart" 35cm Diameter Photomultiplier. Helvetia Physica Acta, 59, 1119 ff., 1986. gprimary ~ 35, st ~ 2.5 ns / Npe KM3NeT WP3 meeting Oct 15, 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

Baikal Quasar 370 X-HPD history

Baikal Quasar 370 G. Hallewell: Centre de Physique des Particules de Marseille Photonis Stargate Meeting 12/9/2007

Baikal Quasar 370 Multi-ports (vacuum + p.c. deposition)

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 present Actors – an expanding group Photonis (B. Combettes, F. Fouche, A-G. Dehaine (relations with Fibrecryst & St Gobain for non organic scintillator crystals + IPNO group (Joel Pouthas et al) for crystal characterisation. INFN Genova (Mauro Taiuti, D. Bersani) CERN (Christian Joram, Andre Bream,Jacques Seguinot) (collaboration wih Photonis – also in-house crystal characterisation) CPPM (Imen Al Samarai*, Greg Hallewell, Jose Busto +..) development contract under GIS IN2P3-Photonis, *funded PhD INR Moscow / Univ. Tuebingen Bayarto Lubsandorzhiev {ex Baikal Quasar 370} + 50% Univ Tuebingen (now a KM3NeT institute) interested to continue development of SMART /Quasar concept under agreement signed with Photonis (2006) on collaboration in joint photodetector development. KM3NeT WP3 meeting Oct 15, 2008

X-HPD history Proposal for NEMO X-HPD with directionality (Mauro Taiuti, Marco Battaglieri et al; INFN Genova) X-HPD with directionality First glass prototype by Soffieria Sestese Metal Flange coupling YSO Scintillator + plexiglass lightguides 4 x Hamamatsu R6427 1 1/8”

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 sph. envelope (improved iso-chronicity + global efficiciency {(# photoelectrons seen)/ (# photons arriving)} ) PMT XP2982 KM3NeT WP3 meeting Oct 15, 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) KM3NeT WP3 meeting Oct 15, 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 X2 compared to a hemispheric PM QE QE KM3NeT WP3 meeting Oct 15, 2008

8’’ Prototype with anode in form of a metal cube (1 cm3) ‘Proto 0’ measured at Photonis ORDINARY BI-ALKALI PHOTOCATHODE !! Fabrication CERN . A. Braem et al., NIM A 570 (2007) 467-474 KM3NeT WP3 meeting Oct 15, 2008

From Joram: Crystal arrangements for X-HPD CERN ‘X-Proto 1’ Anode consists of Al-plated LYSO crystal :12 mm Ø × 18 mm electrical feedthrough Al coated PMT: Photonis XP3102 (25 mm Ø) KM3NeT WP3 meeting Oct 15, 2008

equatorial illumination Extensive remeasurements (June & Sept 2006) of Q.E. of 4 15’’ SMARTS & 1 Quasar acquired by CPPM in early stages of ANTARES Photocathode @ virtual ground linked to Keithley picoammeter scintillator carriage @ +500700V) Tests with polar & equatorial illumination

even with this non-optimal electrostatic configuration Polar & equatorial Q.E. measurements on 4 15” SMARTS + 1 Quasar (June, Sept 2006) We see: Q.E. of 3 of 4 SMARTS still OK, Equatorial enhancement in standard bialkali Q.E., even with this non-optimal electrostatic configuration

Further comments on QE of reflective mode photocathode Semitransparent UBA cathodes now clawing 40-45%: not much more headroom - 50% a natural limit, since no significant electric field (< 100V/cm) inside the cathode bulk in a standard large hemispherical PM  p.e. extraction by random walk with 50% p.e.’s walking to wrong hemisphere; QE QE Reflective photocathodes have higher QE than semi-transparent (CsI – GEM experience) Can be deposited ‘for free’ on aluminium photocathode equipotential conductor surface - which serves no useful detection function in a large PMT - Significant P/V degredation (probably also pre-pusing and after-pulsing) in SBiAl cf standard BiAl In a focussed X-HPD can trade some extra solid angle coverage for much greater QE in sensitive solid angle zone: Al layer keeps more photons in photocathode Extraction field >> than in large hemi. PM KM3NeT WP3 meeting Oct 15, 2008

Example of large X-HPD in 17’’ pressure sphere for KM3NeT: 380 mm Up to ± 120° acceptance Sensitive to single photons TTS 1-2 ns FWHM Q.E. optimised 300 < l < 600 nm dark counts <0.1 per 100 ns Pressure Sphere 17”(432 / 404) Optical gel (matching ref. ind. + coupling to hemisph) 15 Scintillating Crystal Si sensor 432 mm (17”) joint Glass Support ceramic support Small PM Example of large X-HPD in 17’’ pressure sphere for KM3NeT: smaller sizes clearly possible HV PA electrical feed-throughs valve KM3NeT WP3 meeting Oct 15, 2008

Why develop X–HPDs for KM3NeT? Significant uncertainties in the rate of n production at E > ~1014eV ; n telescopes at ~1km3 scale (ICE CUBE) may be nowhere near big enough Probably need ~10 km3 at reasonable OM price: Extend OM Cherenkov horizon or fall into a ‘hole’ where the only detector we can afford to build will be one to detect GZK n’s acoustically… KM3NeT WP3 meeting Oct 15, 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 KM3NeT WP3 meeting Oct 15, 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) KM3NeT WP3 meeting Oct 15, 2008

Effective Surface Ratio: X-HPDs compared to 3 x 10” PMTs/storey KM3NeT WP3 meeting Oct 15, 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 KM3NeT WP3 meeting Oct 15, 2008

ANTARES PM Practical diameter limit to fit in 17’’ pressure sphere Assumptions: Price of Hamamatsu 7081-20 (20cmØ ~16% overall eff): 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

KM3NeT WP3 meeting Oct 15, 2008

Photonis has built 3 prototypes of a new SMART (8”) Photonis has built 3 prototypes of a new SMART (8”) - Internal deposition of the photocathode - Metal disk - measure of photocurrent KM3NeT WP3 meeting Oct 15, 2008

Test stand for metal anode prototypes Equipment: Spellman 25 KV reversible power supply; Black boxes; 4 channel reversible 6KV supply; Keithley 485 picoammeter; LED sources; Ventouse for positioning light source on photocathode Also Simion-8® 3D electrostatic simulation program Will be soon extending stand for crystal prototypes for single photon counting (TTS, pulse height) measurements

Some measurements on first 8’’ prototype (metal disk anode) summer ‘08 Cartography of photocathode with ventouse and 475nm LED (polar angle ‘double cathode’ enhancements seen – and also some azimuthal non-uniformties) nA V q=0° q=15° q=30° q=37.5°  F  8 “ Prototype XP2607 40° polar angle limit Plateau characteristic: LED current set for ~ 1nA on XP2608 at Plateau voltage (measured on Keithley 485 p-ammeter) ~ 30 ph in 50 ns window nA Internal photocathode generators kV Dark current limitation: next Prototype has better pin shielding KM3NeT WP3 meeting Oct 15, 2008

3-D (Simion-8 ®) electrostatic simulation of next Photonis 8” X-HPD with 60° polar angle medal anode prototype – prototype to be tested mid Oct Present anode geometries not optimal: plate not near focal point of envelope (will change this for forthcoming crystal anode prototypes and next metal anode versions) We see however that sub-ns Transit time spread would be reached at~ 5kV (higher voltages will be needed for scintillation light production in crystal) Photonis have identified the glass envelope and internal p.c. deposition as critical to cost – First prototypes (above): all glass envelope & fully internal bialkali photocathode deposition Mid 2008: Fabrication & test of prototype 8” tubes with metal anode WE ARE HERE! First Crystal based proptype from Photonis expected Late November 2008/9: Fabrication & test of 8” HPD tubes with crystal anodes in different configurations Measurement program for of TT, sTT, HT behaviour, l-integrated photocurrent, multi-g res… 2009/2010: Fabrication and test of prototype 15” X-HPD with best crystal anode

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 KM3NeT WP3 meeting Oct 15, 2008

Scintillator Considerations SMART and Quasar tubes used YSO phosphor disk: Geometry didn’t allow to exploit full potential. need to use fast 3-D scintillator shape Require high light yield  high gain short decay time Low Z preferable  low back scattering Emission around l = 400 nm LY (g / keV) t (ns) Zeff eBS lemission (nm) YAP:Ce 18 27 32 ~0.35 370 LYSO:Ce 25 ~40 64 ~0.45 420 LaBr3:Ce 63 30 47 ~0.4 360 Joram, 1st Photonis prototype for CPPM KM3NeT WP3 meeting Oct 15, 2008 LaBr3 is quite hygroscopic

What is the best/cheapest crystal shape (given that 25kV p.e.’s only penetrate a few microns)

What is the best/cheapest crystal shape (given that 25kV p.e.’s only penetrate a few microns)

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 metal anode prototypes + LYSO crystal type (photocurrent, sTT, HT behaviour, multi-g res…) Mid 2008: Fabrication & test of prototype 8” tubes with metal anode End 2008/9: Fabrication & test of 8” HPD tubes with crystal anodes in different configurations 2009/10: Fabrication and test of prototype 15” X-HPD with best crystal anode KM3NeT WP3 meeting Oct 15, 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 much lower than hemispherical PM of same Ø*QE*p.e.coll.eff.) 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) KM3NeT WP3 meeting Oct 15, 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 >50% with standard Bialkali, enhanced overall detection effiency Improved multi-g sensitivity Cost savings through extended Cherenkov horizon: larger water volume instrumented with given number of OMs KM3NeT WP3 meeting Oct 15, 2008

Fin

Photon detectors for water n detectors Large surface area * high Q.E. + good 1g, 2g…? separation or (2): ‘Cluster’ of small PMTs (ou alternative) Classical ‘hemispheric’ PMT Mushroom dome, simple anode, or possibly multi-anode (3) Hybrid (X-HPD) : Acceleration + Scintillator Optical background (ANTARES experience) (single gs in a 20ns counting interval) 40K decays (b’s giving Č light) + Bioluminescence 1g Signal Č on 1g ’’bioK’’ Sometimes 2g Č for m’s close (~10m) to sensors