1 / 30

The Reflective Surface of the MAGIC Telescope

The Reflective Surface of the MAGIC Telescope. Michele Doro on behalf of the MAGIC Collaboration University of Padova & INFN michele.doro@pd.infn.it 6th RICH - Trieste, Italy 15-20 October, 2007. Overview. Part I: The MAGIC detector Overview on the IACT technique

lamis
Download Presentation

The Reflective Surface of the MAGIC Telescope

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Reflective Surfaceof the MAGIC Telescope Michele Doroon behalf of the MAGIC CollaborationUniversity of Padova & INFN michele.doro@pd.infn.it 6th RICH - Trieste, Italy15-20 October, 2007

  2. Overview • Part I: The MAGIC detector • Overview on the IACT technique • Part II: The Reflective Surface • Demands • Mirror • Tests and measurement • MAGIC I problem • MAGIC II upgrade • Overview on future M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  3. PART 1 The MAGIC Telescope

  4. The MAGIC Telescope • Collaboration of 22 institutes (mostly European) ~150 physicists • Installation completed 2003, fully-operating since fall 2004 • ~50 publications on journals • Currently on III-year cycle of scientific-observations M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  5. The IACT technique Physics of the atmospheric showers: • Cosmic rays (protons, heavier Z, electrons, photons) hit the upper atmosphere • Interactions create cascade of billions of particles: • Electromagnetic shower (e+,e-,) • Hadronic shower (, , e+,e-,) • Charged particles in turn emit Cherenkov light: • Blueish flash • ~2ns duration • ~1º aperture • Cherenkov cone reaches the ground • Circle of ~120m radius • Effective telescope area ~ 104-5 m2 M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  6. Imaging Technique • Light is reflected on a multi-pixel camera (576 total) • 396 central PMT 1 inch • 180 outer PMT 1.5 inch • Image is ellipsoid • Pointing to the centre for gammas • Randomly distributed for hadrons • Study of the image gives information on primary particle The reflective surface must ensure a PSF possibly smaller than the pixel size M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  7. Pulsars Physics program AGNs GRBs SNRs ? Origin of Cosmic Rays cosmological g-Ray Horizon Quantum Gravity effects Cold Dark Matter M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  8. MAGIC II • Currently a second telescope is being built • Structurally a clone of MAGIC I • Each system adopted new enhanced solutions • Better telescope than MAGIC I • Stereoscopic MAGIC I + II will have increased performance: • Increased angular resolution • Increased energy resolution • Increased flux sensitivity • Inauguration 21/09/2008 M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  9. Many challenging solutions • Reflector and mirrors: • World largest dish diameter 17m • Light undercarriage made of CFRP • All aluminium mirrors with sandwich structure and diamond-milled surface • Active mirror control • Drive • Faster repositioning ever achieved • Camera • Lacquer-coated enhances photon conversion of PMT • Operation with moonlight • Signal transmission • Ultra-fast acquisition (2GhZ) • Optical transmission instead of coaxial M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  10. PART 2 MAGIC reflective surface

  11. MAGIC I MAGIC II • 2006- MAGIC II mirrors • 1m2 Aluminium mirrors (INFN) • 1m2 Glass mirrors (INAF) Brief History • 2001-2004 MAGIC I mirrors are designed, tested and installed • 732 INFN mirrors (76%) • 224 MPI mirrors (24%) • 2005-06 MAGIC I • Upgrade of the design • Substitution of damaged mirrors M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  12. Mirror Technical Demands M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  13. The Reflector • Parabolic profile • preserve temporal structure of the shower • slightly increased aberrations • Huge dimension demands tessellation of the surface • Radius of curvature changes according to position • So-called average radius used (mean of paraboloid principal radii ) • 34 to 36.5 meters radius range M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  14. Shape • Large reflector area (~234m2) requires to tessellate the surface • Geometry of the mirror tile • Past used solutions: round, hexagonal • Solution: MAGIC has square mirrors to minimize empty regions and easier production • Size • Construction reasons • Aberrations • Solution: MAGIC I has 0.5m side, MAGIC II has 1mside (2x) mirrors M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  15. Materials • Established experience with glass mirrors (astronomy) for other IACTs • 1-2cm thick glass layer • Aluminized for reflectivity • Protection some drawbacks • Usual large weight • Difficulty of producing different focal lengths AlMgSi0.5 plate Hexcell Al-box • Idea of the full-aluminium sandwich • Al-alloy surface • Al-box • Hexcell honeycomb structure • Diamond-milling of the surface Mounting and laser M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  16. MAGIC II 3 Result is the raw-blank 35m Assembly • The sandwich is assembled with the use of the aeronautic glue 3M™ AF163-2K • The sandwich in then inserted between two very-stiff aluminum-moulds • Plane for MAGIC I • Already curved for MAGIC II and everything is put into a plastic vacuum-bag • Autoclave curing • 5 bar pressure • 120º temperature 1 2 M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  17. Diamond-milling • A diamond mills the surface • To give spherical shape, rotation on two axis • Mirror rotates around optical axis • Machine axis rotates tilted and diamong at distance d • Adjustable R curvature • In the MAGIC reflector around 20 different bins of radius of curvatures are needed 3 The mirror gets the reflective properties M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  18. Coating • The aluminium must be protected against environment • Solutions • Diamond chemical vacuum deposition (CVD) • Al2O3 anodization • SiO2 vacuum deposition • Solution adopted: quartz because of costs and transparency in 300-700nm • The width must be optimized for positive interference in the wavelength where Cherenkov light is peaked (blue) • Width ~ 100 nm • Measurement of the roughness gives 4nm on average M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  19. Testing the quality - Reflectivity • The reflectivity was measured in the Cherenkov range (200-800nm) using: • Perkin-Elmer device (mirror must be cut and put inside the machine) • Spectro-photometer (local measure on 3x3cm2 of surface) • MAGIC I: • Reflectivity is correctly peaked at 400nm (close to peak of the Cherenkov spectrum) • Average reflectivity around 80-85% • MAGIC II: • Mantained the same qualities M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  20. MAGIC II mirrors • d90 ~ 5mm • Better of factor 2 • BEST RESULT! LED MAGIC I mirror • d90 ~ 10mm at the camera distance LED Testing the quality - Spot Size • Mirror is put at twice the focal length (~35m) and illuminated with point-like bright source • Analysis of the CCD image: • So-called “d90”= diameter containing 90% of the focused light • d90 = spot size • It is not a measure of reflectivity due to difficulties in estimating scattered light M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  21. Panel & AMC • Major difference between MI and MII • mirrors are grouped into panels of 4 (3 in some cases) • Panel is also Al-sandwich (20kg) • Inter-alignment and fixing • Single mirror host AMC for MII • The back of the panel hosts the actuators for the Active Mirror Control • AMC moves panel to re-adjust the focussing to correct small bending during the tracking • Use of laser M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  22. MAGIC I experience • Main problem with mirrors installed in MAGIC I after two years from installation • Humidity was entering from edge of top plate of the mirrors • Condensation into water • Ice formation and bubbles • Due to strong rigidity, deformation is local and mirror maintains reflective area • Substituted around 100 mirrors (~10%) • Re-designed mirrors for insulation • Test for large mirrors • Now problem seems solved M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  23. SPOT Inner PMT Reflector performance monitor • Reflector performance can be monitored • Reflector PSF, now stable <11mm • Single mirror abs.reflectivity • SBIG CCD at the centre of the reflector, observe a star and the camera at the same time • All mirror focussed:PSF • One mirror focussed and others defocussed: single mirror reflectivity M. GarczarczykPhd Thesis 2007 ~11mm M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  24. Upgrade on MAGIC I • Improved design • Thinner skin and pre-shaped box: the mould is not spherical and the raw-blank comes out already with ~35m curvature • Larger top-plate and gluing of the edge with 3M™ DP190 • External heater to avoid coupling between plastic and aluminium M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  25. MAGIC II Al-mirrors • Basically an extension of MAGIC I-upgraded mirror: • Larger upper plate with respect to box • Use of aeronautic glue DP190 for insulation • No internal heater • Curvable box • Increased honeycomb width resulted in increased rigidity: • Best spot size due to more accurate diamond milling of the surface MAGIC I MAGIC II M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  26. MAGIC II • MAGIC II will have • 144 m2 of INFN-Padova mirrors • 104 m2 of INAF-Brera mirrors • Upgrade to 1m2 facet • Technologically achievable • Less number of items • Decreased weight and direct coupling to active mirror control • No-need of inter-alignment • Drawback: • Less approximating the parabola: increased aberrations, nevertheless the coma aberration dominates for tilted incidence M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  27. MAGIC II Glass mirrors • A thin glass sheet (1-2 mm) is elastically deformed so to retain the shape imparted by a mould having convex profile. If the radius of curvature is large, the sheet can be pressed against the mould using the vacuum suction. • On the deformed glass sheet (under vacuum force) is glued an honeycomb structure that provide the structural rigidity. • Then a second glass sheet is glued on the top to create a sandwich. • After releasing the vacuum, on the concave side is deposited a reflecting design for their mirrors coating (Aluminum) and a thin protective coating (Quartz) M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  28. Summary and outlook • MAGIC II mirrors production is already on the production-line • Technique gave excellent results in term of light concentration • Insulating problems seem solved • Price is decreased wrt to MAGIC I, nevertheless is still main drawback: 2.8k€/m2 can be a problem for third generation IACTs • Scale production can decrease costs or find other techniques (glass) M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

  29. Back-up slides

  30. Results • Around 50 publications on journals • ~21 VHE source observed (6 MAGIC discoveries!) • 7 new analysis techniques • 23 technical papers • Observed sources: • 12 = extragalactic • 9 = galactic http://tevcat.uchicago.edu/ M.Doro - The Reflective Surface of the MAGIC Telescope - RICH 2007

More Related