Multi-PMT DOM P.Kooijman University of Amsterdam-GRAPPA Presentation for SSC

KM3NeT DOM Self-contained “plug-and-play” module (17” diameter) with – Photo-sensors 31 (19+12) 3” PMTs Equivalent of 4 x 8” PMTs – Includes: All read-out/control electronics Calibration devices – Single penetrator for connection to an e/o backbone cable

History: VLVnT 2003 “Esso“ Flyckt (Photonis):  Multiple small (inexpensive) PMTs/OM  Quantum efficiency higher then for large tube  High design flexibility  Ready for production; unlimited capacity! (PET)  “Come and get them“

His drawing

Current drawing Looks similar – but LOTS of development

Long time considering different configurations Simulations in thesis S. Kuch -> sphere best Design -> sphere many advantages

Distinguish single from multiple photon hits: Photon counting = PMT counting Photons are quantised Background rejection – 40 K Looking upward: Background rejection – atmospheric muons More uniform angular acceptance Directionality: Signal photons from one side Initially: why multi-PMT OM?

Additionally: why multi-PMT OM? Deep Sea constraints: One penetrator for large photocathode area Handling and assembly (See Els) : Small PMTs Less glass spheres No separate electronics container New Insights: Measurements from Antares on large PMTs

Additionally: why multi-PMT OM? Antares 10” PMT amplitude [p.e.] number of events [a.u.] Antares 10” PMT Gauss (  = 0.4 p.e.) non Gaussian tail amplitude [p.e.] probability lowbioluminescence highbioluminescence (x ~ 3) tail is rate independent (therefore not due to 40 K in glass) Large PH in large tubes

amplitude [p.e.]  t [ns] number of events [a.u.] 1 p.e. peak late after pulses early after pulses Additionally: why multi-PMT OM? In multi-PMT DOM we see real large photon fluxes with more than one tube.  Less sensitive to single tube noise Late after pulses

Major constraint: Power No communications laser: REAM (see Frederic) HV generation for PMT: New Cockroft-Walton design (Nikhef) Adjustable HV ( V) Diameter 38 mm – Space Power < 4.5 mW Reduce Integrated Charge: ASIC with pre-amplifier and discriminator (time-over- threshold)

PMT: Initially Photonis XP53B20 Ten stage PMT developed from PET scanner tubes Production at the time ~90000 per year High reliability Insensitive to Magnetic field Modified for timing – concave photocathode Modified for fitting in sphere – convex front Photonis stopped producing ~2 years delay

PMT: Expansion cone Addition of reflective expansion ring: Added convenience for holding Increase sensitive area of 40% for front illumination Increase of 20% integrated over 2 

Critical Point – PMT production Photonis no longer manufacturing Contacts with four manufacturers ETEL custom made tube  First delivery imminent Hamamatsu modification of existing  First delivery Jan 2011

First Measurements

PMT suspension Foam core: Light Sturdy Cheap (moulding) Insulation of cathode

Temperature measurements Heat-load 10 W

Cooling Mushroom Heat conducting foil Power board Logic board (dummy) On shield On Mushroom Foam core with PMTs (temperature sensor cabling) Assembly of DOM Pour optical gel DOM components

Closing the DOM

Instrumentation inside DOM Acoustic piezo element (position cal.) Compass/tilt metre Nanobeacon (timing calibration) Charge calibration – Threshold level and high voltage combination set before deployment – 40 K after deployment  Gain relatively low  Collected charge low  Predicted gain variations small

16 Optical Fibers Silicon Seal Glass Epoxy Plate Conical Plug Test flange Hera pressure vessel Tested to 60 MPa -- success Also through glass Feedthrough – tapered plug Has to carry several conductors and a fibre Has to withstand 600 Bar (60 Mpa) Companies provide bulkhead connectors and penetrators with O ring technology at large price

Conclusions Design worked out and verified in detail Phototubes still critical  Await measurements of ETEL tubes  Negotiations with Hamamatsu All other components under control Total power has to be kept under control