1. The Multi-PMT Optical Module P.Kooijman, University of Amsterdam University of Utrecht Nikhef

2. What is a Multi PMT optical module? Why build a Multi PMT optical module? Requirements Status How to build one CONTENT

3. 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

4. Why build a Multi PMT optical module? Can put much more photo- cathode area in a single pressure sphere ‐1260 cm 2 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 ‐ 40 K background Less sensitive to failure

5. 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

6. 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 10 6 Photonis is no more for PMTs Hamamatsu has provided prototype (plano-convex) Discussions with ETL towards a prototype concave convex

7. 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 Converter board for DC/DC converters. Shielded by Aluminium Space for other instrumentation also on auxiliary boards

8. Estimate 10 W 31 * 30 mW (HV 4.5 mW) (D) DC/DC converters (A) FPGA etc. (B) Data transmission electronics (B) POWER DISSIPATION Aluminium Cooling Mushroom

9. TEMPERATURE TESTS Temperatures remain low in tests 4W on each electronics board 60 mW on PMT base T 1 ( o C) T 7 ( o C) T 9 ( o C) T 11 ( o C) T 12 ( o C) T 13 ( o C) 20.4/22.8 19.6/21.2 17.1/14.1 23.7/26.8 20.2/22.8 19.9/19.2

10. CONSTRUCTION add optical gel lower hemisphere

11. CONSTRUCTION upper hemisphere glue add optical gel storage closing the sphere Light-tight box

12. 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

13. 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)