The Multi-PMT Optical Module

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The Multi-PMT Optical Module

• P.Kooijman,
• University of Amsterdam
• University of Utrecht
• Nikhef

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CONTENT

• What is a Multi PMT optical module?
• Why build a Multi PMT optical module?
• Requirements
• Status
• How to build one

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WHAT IS A MULTI PMT OPTICAL MODULE?

• An optical module containing many small PMTs
  rather than one big one
• Contains all electronics necessary to read out
  and control the module
• Is a self contained unit

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Why build a Multi PMT optical module?

• Can put much more photo-cathode area in a single
  pressure sphere
• 1260 cm2 or more with ring ( Oksana )
• More compact design
• Only one sphere to handle
• 3 PMT easy to manipulate
• 1 sphere vs 3 spheres
• Quite uniform angular acceptance.
• Reconstruction of downward going muons
• Counting photons counting PMTs
• 90 of all 2spe hits are 2PMT hits
• 40K background
• Less sensitive to failure

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REQUIREMENTS

• Can fit sufficient photomultipliers in a
  reasonably sized sphere
• 31 3 Photomultipliers in a 17 sphere
• Supported by foam
• Optical contact through gel
• Can house the HV generation inside sphere.
• Special HV low power including amplifier
• Readout electronics must not be 31times
• Time over threshold readout
• House readout electronics in sphere
• Power dissipation must not lead to excessive
  temperature inside the sphere
• Reliability at the level of a few percent
  failures for ten years

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PHOTOMULTIPLIERS

• Was a Photonis tube XP53B20
• 76 mm cathode diameter
• Bialkali cathode, Q.E. 35
• Convex front matching sphere
• 10 stage
• Gain 5 (1) x 106
• Photonis is no more for PMTs
• Hamamatsu has provided prototype (plano-convex)
• Discussions with ETL towards a prototype

concave
convex
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ELECTRONICS BOARDS
HV on the back of PMT together with amplifier and
comparator. Signals collected on stem of
mushroom Storey logic board for signal
processing and communications electronics Convert
er board for DC/DC converters. Shielded by
Aluminium Space for other instrumentation also
on auxiliary boards
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POWER DISSIPATION

• Estimate 10 W
• 31 30 mW (HV 4.5 mW) (D)
• DC/DC converters (A)
• FPGA etc. (B)
• Data transmission electronics (B)

Aluminium Cooling Mushroom
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TEMPERATURE TESTS
Temperatures remain low in tests 4W on each
electronics board 60 mW on PMT base
T1 (oC)
T7 (oC)
T9 (oC)
T11 (oC)
T12 (oC)
T13 (oC)
20.4/22.8
19.6/21.2
17.1/14.1
23.7/26.8
20.2/22.8
19.9/19.2
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CONSTRUCTION
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CONSTRUCTION
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TESTING
Acceptance testing PMTs (200000 or 1000 /week
) Bases (200000 or 1000 /week ) PC boards
(2x6000 or 60/week ) Assembly testing Go/nogo
test top half of module Go/nogo test of
installed PC boards and connectivity Go/nogo
test lower half Test of full optical module
Standalone using complete readout Burn in and
functionality (30/week) Final test before
mounting on DU only connectivity
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CONCLUSIONS

• The Multi PMT optical module
• Is
• Compact (lots of photocathode area)
• Standalone (tests and failures only affect one
  module)
• Reliable (necessary FIT rates are achievable)
• Buildable almost anywhere (no large assembly hall
  needed)
• Has
• Acceptance uniformity (muon background)
• High granularity (two photon sensitivity)

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