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

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Presentation on theme: "All-aluminum mirrors for the MAGIC Cherenkov Telescope Nadia Tonello, for the MAGIC Collaboration Why all-aluminum mirrors Technical characteristics of."— Presentation transcript:

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 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München2 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 cm 2 sandwich construction

3 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München3 The MAGIC Telescope ORM, La Palma (Canary Islands) Mirrors area239 m² Camera576 pixels FOV4°4° Energy threshold30 GeV Positioning time< 40 s

4 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München4 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

5 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München5 Performance Reflectivity vs. wavelength for a coated mirror Roughness = 4.1 nm 87% on av. between 300 and 650 nm (sensitivity region of the PMTs)

6 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München6 Focal spot studies Shape and size of the spot: measurement of the effective radius of curvature. Light distribution from the center of the spot 90% of the light is collected in a circle ~30% of a pixel ø 6 cm Measurements taken at 2* focal length

7 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München7 Assembling and alignment The mirrors are assembled in panels of 4, pre- aligned and fixed.

8 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München8 Installation on the telescope The panels are installed in the main frame. The active mirror control allow to align the panels (MG talk)

9 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München9 Summary Size of a mirror 0.25 m 2 Weight of a mirror 3.5 kg Reflectivity (incl. coating) ≥ 85 % Roughness 4.1 nm Average spot size (90%) 1 cm  Mirror production state: 750 / 959 Panels installation state: 98 / 245

10 DPG Tagung, March 2003Nadia Tonello, MPI für Physik, München10 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 length during 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 m 2 mirrors of aspheric surface. The new technology mirrors are a good alternative to glass mirrors.


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