All-aluminum mirrors for the MAGIC Cherenkov Telescope Nadia Tonello, for the MAGIC Collaboration...
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Transcript of All-aluminum mirrors for the MAGIC Cherenkov Telescope Nadia Tonello, for the MAGIC Collaboration...
All-aluminum mirrors for the MAGIC Cherenkov Telescope
Nadia Tonello, for the MAGIC Collaboration
Why all-aluminum mirrorsTechnical characteristics of the mirrorsPerformanceSummary
DPG Tagung, March 2003 Nadia 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 cm2 sandwich construction
DPG Tagung, March 2003 Nadia Tonello, MPI für Physik, München3
The MAGIC TelescopeORM, La Palma
(Canary Islands)
Mirrors area 239 m²
Camera 576 pixels
FOV 4°
Energy threshold 30 GeV
Positioning time < 40 s
DPG Tagung, March 2003 Nadia 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
DPG Tagung, March 2003 Nadia Tonello, MPI für Physik, München5
PerformanceReflectivity vs. wavelength for a coated mirror
Roughness = 4.1 nm
87% on av. between 300 and 650 nm (sensitivity region of the PMTs)
DPG Tagung, March 2003 Nadia 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
DPG Tagung, March 2003 Nadia Tonello, MPI für Physik, München7
Assembling and alignment
The mirrors are assembled in panels of 4, pre-aligned and fixed.
DPG Tagung, March 2003 Nadia 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)
DPG Tagung, March 2003 Nadia Tonello, MPI für Physik, München9
SummarySize of a mirror 0.25 m2
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 / 959Panels installation state:98 / 245
DPG Tagung, March 2003 Nadia 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 m2 mirrors of aspheric surface.
The new technology mirrors are a good alternative to glass mirrors.