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All-aluminum mirrors for the MAGIC Cherenkov Telescope

All-aluminum mirrors for the MAGIC Cherenkov Telescope. Nadia Tonello, for the MAGIC Collaboration. Why all-aluminum mirrors Technical characteristics of the mirrors Performance Summary. Motivations. Reduce the weight of the mirrors: limited deformation of the main frame,

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All-aluminum mirrors for the MAGIC Cherenkov Telescope

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  1. All-aluminum mirrors for the MAGIC Cherenkov Telescope Nadia Tonello, for the MAGIC Collaboration Why all-aluminum mirrors Technical characteristics of the mirrors Performance Summary

  2. Motivations • Reduce the weight of the mirrors: • limited deformation of the main frame, • rapid positioning for GRB alert • Parabolic (isochronous) mirror profile: • many different radii of curvature, difficult to make it with glass mirrors • Heating system: • avoid problems of dew (ice) • Reduce costs SOLUTION: diamond milled all-aluminum mirrors 50 x 50 cm2 sandwich construction Nadia Tonello, MPI für Physik, München

  3. The MAGIC Telescope ORM, La Palma (Canary Islands) Nadia Tonello, MPI für Physik, München

  4. Technical view of a mirror All-aluminum 50x50 cm ² sandwich = light weight (~ 4kg) Original development at MPI (Munich), production of improved raw blanks in Padua (I) • Diamond milled reflecting surface • Heating system • Light and stiff honey-comb structure The mirrors are mounted in panels before the installation 1.0 Nadia Tonello, MPI für Physik, München

  5. Performance Roughness = 4.1 nm Reflectivity vs. wavelength for a coated mirror 87% on av. between 300 and 650 nm (sensitivity region of the PMTs) Nadia Tonello, MPI für Physik, München

  6. Focal spot studies Shape and size of the spot: measurement of the effective radius of curvature. 6 cm Light distribution from the center of the spot Measurements taken at 2* focal length 90% of the light is collected in a circle ~30% of a pixel ø Nadia Tonello, MPI für Physik, München

  7. Assembling and alignment The mirrors are assembled in panels of 4, pre-aligned and fixed. Nadia Tonello, MPI für Physik, München

  8. Installation on the telescope The panels areinstalled in the main frame . The active mirror control allow to align the panels (MG talk) Nadia Tonello, MPI für Physik, München

  9. Summary Mirror production state: 750 / 959 Panels installation state: 98 / 245 Nadia Tonello, MPI für Physik, München

  10. Conclusions • Production of light weight mirrors (weight :1/2 of glass mirrors) . • Optical quality matches glass mirrors. • Technology of diamond milling allows to change easily the focal lengthduring production (for parabolic profile). • Cost of diamond milling = 290 € ( incl. quartz coating) • Prototypes installed in HEGRA CT1 show good quality after 5 years exposure. • Control of the optical surface of the telescope with AMC (M.G. talk) • Preparing next generation of 1 m2 mirrors of aspheric surface. The new technology mirrors are a good alternative to glass mirrors. Nadia Tonello, MPI für Physik, München

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