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NLST – National Large Solar Telescope
India’s Plan for a New, Large Solar Telescope
D. Soltau (KIS), Th. Berkefeld (KIS), M. Süß (MTM), H. Kärcher (MTM)
1st EAST & ATST Workshop, Freiburg, 14.-16.10. 2009
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NLST Fills a Gap
3
Diffraction-limited images: D = 2 m
630 nm continuum6 Mm 6 Mm1152 1152 pixels(size 5.2 km)
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Requirements
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Additional Requirements
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Specs
• Aperture: 2 m• f/40
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Designer‘s Dream
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Design Philosophy
• A solar telescope has to provide– High resolution– Potential for high precision polarimetry– Potential for high performance post focus equipment– Good internal seeing
• NLST in particular– High throughput– FOV = 200”– AO integrated– Only calculated technical risks– Night Time Applications– Potential for fast realization– Cost effective
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GREGOR
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A Starting Point: GREGOR
• D = 1.5 m• f/38• 16 mirrors
• Boundary conditions were:– Existing building had to be used
• Dome diameter fixed
– High Order AO not affordable (at project start)
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NLST, The Proposed Design
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M1
F1
M2
F2polarimetry
M3
M4
M5 (DM)
M6 (TT)
M7 F4
Field lens
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High Throughput
• NLST will allow for short exposures– Advantage for polarimetry– Advantage for speckling
GREGOR NLST EST
0.00E+000
2.00E+011
4.00E+011
6.00E+011
8.00E+011
1.00E+012
1.20E+012
1.40E+012
1.60E+012
1.80E+012Photon flux/s/nm/arcsec^2
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Image quality +/- 100 arcsec
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Image Quality: PSF
• FWHM = 25 µm = 0.06 arcsec
• Center of field
• 100 arcsec field
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Some features
• M1 cooled (air)• M2 on hexapod (part of the active optics control system)• Liquid cooled F1 field stop• Space (400 x 200 mm) for polarization optics• Focusing done with M3. Focus can be shifted > +/- 1 m• Pupil diameter for DM 180 mm (matches DM Specs)• Final image scale: 2.6 arcsec/mm
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Integrated AO?
• There is always a pupil (image of M1) near F1 produced by M2 which always has about 20% of M1 diameter
• For a telescope larger than 1.5 m most reasonable M3 will produce a pupil inside the telescope tube
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Integrated AO
• Pupil image on DM by means of a weak negative field lens made of fused silica
• Exit pupil not at infinity
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Integrated AO
At least 496 actuators428 subapertures
25 subaps across
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HODM (by CILAS)
Credit to M. Kasper, ESO
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The Field Lens and Pupil Guiding
• The Field lens could be used for pupil guidung:– 1 subaperture correspond to about 6 mm on M5
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Telescope structure
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Telescope structure
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There are always two azimuth positions
Moderate windspeeds: ideal for natural air flushing
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Mechanical structure
• Elevation structure: Carbon fibre composite (CFRP)
• Azimuth structure: Steel
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Frequencies
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Dome
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Observing floor
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CFD Analysis
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CFD Analysis
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Summary
• India has serious plans to build a 2m class solar telescope
• There are site candidates with promising quality
• There is an optical design which is characterized by
– Simplicity
– High Throughput
– High order AO
– Good cooling preconditions (Large heat stop, cooled M1)
• There is a mechanical design which is characterized by
– Filigrane structure (carbon structure)
– Asymmetry allowing two azimuth positions
– M1 well above ground
• There is a raw design for a fully retractable dome
• There is a raw design for an aerodynamically optimized building and platform
NLST can (hopefully) see first light in 2014 and be the largest solar telescope until ATST is finished
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NLST