X -HPD Optical Module R D for KM 3 Ne

X*-HPD Optical Module R&D for KM 3 Ne. T (*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 Quasar 370 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-IN 2 P 3 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 KM 3 Ne. T WP 3 meeting Oct 15, 2008

From… Presentation by B. Combettes (Photonis) Identified as a major Photonis priority for n detectors NNN 07, Hamamatsu, Japan, October 2007 Reiterated at NNN 08, APC, September 2008

Presentation m What is the X-HPD? m History of the X-HPD; m X-HPD advantages – why develop it? m Who are the actors? m Present status inc R&D at CPPM; m Future developments KM 3 Ne. T WP 3 meeting Oct 15, 2008

What is the X-HPD? First of all, what it ISN’T… KM 3 Ne. T WP 3 meeting Oct 15, 2008

It isn’t like the LHC-b HPD (DEP Photonis) shown here… v is big, like a hemispherical PM; v has standard bi-alkali p. c. and borosilicate window; v has no electronics in the vacuum volume; v is compatible with internal photocathode processing like PM; v is insensitive to the Earth’s magnetic field; (photoelectrons accelerated in ~25 k. V) Under vacuum, the X-HPD contains (only…) : v v v 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 KM 3 Ne. T WP 3 meeting Oct 15, 2008 120 mm The X-HPD : 80 mm

What is the X-HPD? v A “simple” detector of single photons with a bialkali p. c. v High accelerating field (~25 k. V) between p. c. & scintillating crystal (short Tdecay) under thin metallic layer (Al, 100 nm) v Preferably a completely spherical geometry, with scintillator at the centre Eff. for electrostatic collect. + (Standard Bialkali) Q. E èGlobal Efficiency ≥ 33% (40% av. ~50% max) (cf ~16% hemispherical PM) KM 3 Ne. T WP 3 meeting Oct 15, 2008

The first crystal-HPD: Philips SMART : Phosphor P 47 (YSO: Ce) ~30 manufactured (1980 s-1992) History of the X-HPD G. van Aller et al. A "smart" 35 cm Diameter Photomultiplier. Helvetia Physica Acta, 59, 1119 , (1986). KM 3 Ne. T WP 3 meeting Oct 15, 2008

8 grains of Sb (deposition of PC) P 47 (YSO: Ce) phosphor Deposited on glass Sb deposition shield (+25 k. V) Domed +25 k. V surface Quasi-internal photocathode deposition (NOT A TRANSFER PROCESS)…! KM 3 Ne. T WP 3 meeting Oct 15, 2008

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

Baikal Quasar-370 (1983 ) Hybrid (X-HPD) -Hemispherical dome =370 mm -Photocathode K 2 Cs. Sb -Preamplification 25 k. V -Scintillator Y 2 Si. O 5 (TTS= 2 ns FWHM) - Traditional PMT K 2 Cs. Sb 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 R. Bagduev et al. , Nucl. Instr. Meth. A 420 (1999) 138 Quasars in operation since 1993: 200 since 1998

The present Actors – an expanding group m 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. m INFN Genova (Mauro Taiuti, D. Bersani) m CERN (Christian Joram, Andre Bream, Jacques Seguinot) (collaboration wih Photonis – also in-house crystal characterisation) m CPPM (Imen Al Samarai*, Greg Hallewell, Jose Busto +. . ) development contract under GIS IN 2 P 3 -Photonis, *funded Ph. D m INR Moscow / Univ. Tuebingen Bayarto Lubsandorzhiev {ex Baikal Quasar 370} + 50% Univ Tuebingen (now a KM 3 Ne. T institute) interested to continue development of SMART /Quasar concept under agreement signed with Photonis (2006) on collaboration in joint photodetector development. KM 3 Ne. T WP 3 meeting Oct 15, 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 sph. envelope (improved iso-chronicity + global efficiciency {(# photoelectrons seen)/ (# photons arriving)} ) PMT XP 2982 KM 3 Ne. T WP 3 meeting Oct 15, 2008

CERN - Photonis: Toward Development of a large spherical X-HPD hybrid photodetector A. Braem +, C. Joram +, J. Séguinot +, L. Pierre *, P. Lavoute * + CERN, Geneva (CH) * Photonis SAS, Brive (F) KM 3 Ne. T WP 3 meeting Oct 15, 2008

Advantages of a spherical tube with anode at geometric centre • Radial electric field à s TTS negligeable à Efficiency of electrostatic collection ~100% over ~ 3 p Sr To be compared with : ~ 70% over only 4 p/3 Sr in a hemispherical PM! à Mu-metal screen unnecessary Nesessary for a hemispheric PM àLarge detection solide angle (d. W ~ 3 p) QE X 2 compared to a hemispheric PM à Gain in effective QE sensitivity by ‘Double- passage’ effect through photocathode QE KM 3 Ne. T WP 3 meeting Oct 15, 2008

8’’ Prototype with anode in form of a metal cube (1 cm 3) ‘Proto 0’ measured at Photonis ORDINARY BI-ALKALI PHOTOCATHODE !! Fabrication CERN. A. Braem et al. , NIM A 570 (2007) 467 -474 KM 3 Ne. T WP 3 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 XP 3102 (25 mm Ø) KM 3 Ne. T WP 3 meeting Oct 15, 2008

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 @ +500 700 V) Tests with polar & equatorial illumination

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 QE Significant P/V degredation (probably also pre-pusing and after-pulsing) in SBi. Al cf standard Bi. Al • Semitransparent UBA cathodes now clawing 40 -45%: not much more headroom - 50% a natural limit, since no significant electric field (< 100 V/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; • Reflective photocathodes have higher QE than semi-transparent (Cs. I – GEM experience) • Can be deposited ‘for free’ on aluminium photocathode equipotential conductor surface - which serves no useful detection function in a large PMT - • 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 KM 3 Ne. T WP 3 meeting Oct 15, 2008

380 mm Optical gel (matching ref. ind. + coupling to hemisph) 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 15 432 mm (17”) joint • Scintillating Si sensor Crystal Glass ceramic Support support Small PM Pressure Sphere 17”(432 / 404) Example of large HV X-HPD in 17’’ pressure sphere for KM 3 Ne. T: smaller sizes clearly possible electrical feedthroughs KM 3 Ne. T WP 3 meeting Oct 15, 2008 PA valve

Why develop X–HPDs for KM 3 Ne. T? Significant uncertainties in the rate of n production at E > ~1014 e. V ; n telescopes at ~1 km 3 scale (ICE CUBE) may be nowhere near big enough Probably need ~10 km 3 at reasonable OM price: èExtend 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… KM 3 Ne. T WP 3 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 3 p 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 km 3) separated by 85 m. Each line 34 storeys spaced at 15 m ANTARES site parameters KM 3 Ne. T WP 3 meeting Oct 15, 2008

Evaluating the advantages of Spherical format X-HPDs: Volume /cost sensitivity comparison with 10” Hamamatsu R 7081 -20 used in ANTARES Assumptions m ~350 Cherenkov photons per cm (300 -600 nm) m Attenuation length 35 m (combined absorption, scattering) m Photon flight 40 m/sinq. C (q. C = 43°) =56 m m Cost per ANTARES OM = PM: 995€, electronics: 600€, mechanics: 660€, sphere+other 600€ m 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 KM 3 Ne. T WP 3 meeting Oct 15, 2008

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

Photonis has built 3 prototypes of a new SMART (8”) - Internal deposition of the photocathode - Metal disk - measure of photocurrent KM 3 Ne. T WP 3 meeting Oct 15, 2008

Test stand for metal anode prototypes Equipment: • Spellman 25 KV reversible power supply; • Black boxes; • 4 channel reversible 6 KV supply; • Keithley 485 picoammeter; • LED sources; • Ventouse for positioning light source on photocathode Also Simion-8® 3 D 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 475 nm LED (polar angle ‘double cathode’ enhancements seen – and also some azimuthal non-uniformties) 8 “ Prototype XP 2607 40° polar angle limit 1 n. A 0. 1 Plateau characteristic: LED current set for ~ 1 n. A on XP 2608 at Plateau voltage q=37. 5° (measured on Keithley 485 p-ammeter) ~ 30 ph in 50 ns window q=30° q=15° V 0 1, 000 q=0° F 800 600 n. A 400 200 0 Internal photocathode generators 0 5 10 k. V 15 Dark current limitation: next Prototype has better pin shielding KM 3 Ne. T WP 3 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 m m m Present anode geometries not optimal: plate not near focal point of envelope (will change this forthcoming crystal anode prototypes and next metal anode versions) We see however that sub-ns Transit time spread would be reached at~ 5 k. V (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, s. TT, HT behaviour, l-integrated photocurrent, multi-g res… 2009/2010: Fabrication and test of prototype 15” X-HPD with best crystal anode

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 / ke. V) t (ns) YAP: Ce 18 27 32 ~0. 35 370 LYSO: Ce 25 ~40 64 ~0. 45 420 La. Br 3: Ce 63 30 47 ~0. 4 360 La. Br 3 is quite hygroscopic Zeff e. BS lemission (nm) KM 3 Ne. T WP 3 meeting Oct 15, 2008 Joram, 1 st Photonis prototype for CPPM

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

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

Near future developments m m 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 NDIP 2008, June 2008) Parallel crystal studies (CERN-Photonis, IPN Orsay) At CPPM, measurements of metal anode prototypes + LYSO crystal type (photocurrent, s. TT, 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 KM 3 Ne. T WP 3 meeting Oct 15, 2008

Conclusion v Pure spherical geometry X-HPDs based on Flyckt/Van Aller Philips SMART tube could be very promising Čg – detectors for underwater n telescopes v ~100% photoelectron collection eff. (over 3 p Sr) (& s. TT<1 ns ) (c. f. 65% over ~ 4 p/3 cathode surface area in ‘hemispherical’ PM) v Much larger photocathode area than same Ø hemispherical PM + suppression of m-metal cage v Improved Q. E. (transmissive reflective) over large % of 3 p >50% with standard Bialkali, enhanced overall detection effiency v Improved multi-g sensitivity èCost savings through extended Cherenkov horizon: larger water volume instrumented with given number of OMs KM 3 Ne. T WP 3 meeting Oct 15, 2008

Fin

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