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Recent Results of the Measurement of the Angular Acceptance of the Optical Modules

Recent Results of the Measurement of the Angular Acceptance of the Optical Modules. M.Taiuti KM3NeT Work Packages meeting Joint meeting WP2, WP3, WP4, WP5 Paris 15 October 2008. OUTLINE. The Status of the Integration of the Direction Sensitive Optical Module (DOM)

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Recent Results of the Measurement of the Angular Acceptance of the Optical Modules

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  1. Recent Results of the Measurement of the Angular Acceptance of the Optical Modules M.Taiuti KM3NeT Work Packages meeting Joint meeting WP2, WP3, WP4, WP5 Paris 15 October 2008

  2. OUTLINE • The Status of the Integration of the Direction Sensitive Optical Module (DOM) • Description of the Testing Devices available in Genova • Measured Properties of the DOM • Comparison with ANTARES OM

  3. The Direction Sensitive Optical Module • Ingredients • An optical module à la ANTARES or NEMO • 1 Multianodic PMT • Mirrors • Advantages • Improved effective area and angular resolution at low neutrino energy at constant collected light NEMO ANTARES <2° <2°

  4. PMT Frame PMT 10” 4-anods Optic gel (8 cm) Mu-metal Sphere 17” Highly reflective mirrors The DOM Lay-out

  5. The DOM Integration • The procedure is similar to ANTARES and NEMO • In addition: • The mirrors has to be prepared and pre-assembled on a frame • A larger amount of optical gel is required • The electronics include a circuitry to suppress the inter-anodic cross-talk

  6. The DOM integration STEP1: PMT+Mirrors Coupling 1 – The mirrors are mounted on a frame (later removed) 2 – The PMT is mounted on the same frame

  7. The DOM integration STEP2: Assembly of lower hemisphere 3 – The PMT+mirror system is added 2 – Gel is poured in the hemispehere containing the mu-metal 1 - Optic gel is prepared 4 – Gel polimerizes in vacuum

  8. PMT TRIGGER OM located inside a water vessel m m q The Testing Facilities: Angular Acceptance • In Genova we measured the angular acceptance and the photocathode quantum efficiency of two ANTARES OMs and one DOM prototype • Angular acceptance testing device

  9. Reference detector B Removable monitor detector A splitter Optical Module laser 439 nm collimator The Testing Facilities: the Local Q.E. • Absolute quantum efficiency testing device

  10. m Cherenkov Light q The DOM Optical Properties • The angular acceptance At >0° one sector (that looking upward) dominates - OK At =0° all sectors contribute to the same amount - OK

  11. m Cherenkov Light q The DOM Optical Properties • Comparison with MonteCarlo simulations: • Farily good agreement for the full response of the optical module (circle) - OK • Directionality less effective than expected: larger contribution from other sectors (squares and triangles) - WHY? • Reasons • Probably the not well defined photocathode subdivision

  12. A1 A4 A2 A3 Scanning line Sector 1 Sector 4 Sector 2 Sector 3

  13. The DOM Optical Properties: Q.E. Hamamatsu test result • The Quantum Efficiency • Smaller than bare PMT (15%) but compatible with simulations - OK • Sector 3 shows lower Q.E. - to be investigated • Drop at large angles too smooth (the gel ends at 75°) - to be investigated Sector 3 Sector 1 Drop at large angles mainly related to border effects (end of optic gel)

  14. R R The DOM and the ANTARES OM Properties • Comparison of the angular acceptance with ANTARES OM shows similar behaviour at small angles (<60°) – OK • At larger angle the DOM looks worse - WHY? • The measured acceptances agree with Montecarlo simulations therefore the possible reason could be the different geometry

  15. The DOM and the ANTARES OM Properties • The ANTARES Q.E. decreases at large angles and drops at angles larger than 35° • The DOM shows uniform QE up to 60° - OK • Reason for drop of Q.E.: geometrical cut due to optic gel ANTARES OM DOM

  16. DOM Costs • Compared to ANTARES OM, the DOM has some extra costs: • PMT (from Hamamatsu) • Optical gel (8kg/module) 384 € • HV divider and electronic board 100 € R7081MOD (4-anods, std. photocathode)5000 pcs  1053 euro/pcs10000 pcs  1001 euro/pcsR7081MOD (4-anods, QE  32%)5000 pcs  1420 euro/pcs10000 pcs  1356 euro/pcs

  17. CONCLUSIONS • The measured performancies of DOM agree with design project except for: • the not well defined border between photocathode sectors that affects the sensitivity to direction (problem related to the quality of the PMT prototype) • the non completely understood drop of the Q.E. at the border

  18. Mechanical possibilities

  19. 4-anodic PMT Compatibility • The 4-anodic PMT perfectly fits in the String-3OM and Tower-4OM solutions with Optical Modules à la ANTARES

  20. 4-anodic PMT Alternate Solution • The 4-anodic PMT perfectly fits in the 13” sphere solution when the mirrors are removed • In this case the information on the direction of the detected light is lost, but the large angular acceptance remains

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