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

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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