1 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) 1 st EAST & ATST Workshop, Freiburg,

2 NLST Fills a Gap

3 Diffraction-limited images: D = 2 m 630 nm continuum 6 Mm  6 Mm 1152  1152 pixels (size 5.2 km)

4 Requirements

5 Additional Requirements

6 Specs Aperture: 2 m f/40

7 Designer‘s Dream

8 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

9 GREGOR

10 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)‏

11 NLST, The Proposed Design

12 M1 F1 M2 F2 polarimetry M3 M4 M5 (DM) M6 (TT) M7F4 Field lens

13 High Throughput NLST will allow for short exposures –Advantage for polarimetry –Advantage for speckling

14 Image quality +/- 100 arcsec

15 Image Quality: PSF FWHM = 25 µm = 0.06 arcsec Center of field 100 arcsec field

16 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

17 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

18 Integrated AO Pupil image on DM by means of a weak negative field lens made of fused silica Exit pupil not at infinity

19 Integrated AO At least 496 actuators 428 subapertures 25 subaps across

20 HODM (by CILAS) Credit to M. Kasper, ESO

21 The Field Lens and Pupil Guiding The Field lens could be used for pupil guidung: –1 subaperture correspond to about 6 mm on M5

22 Telescope structure

23 Telescope structure

24 There are always two azimuth positions Moderate windspeeds: ideal for natural air flushing

25 Mechanical structure Elevation structure: Carbon fibre composite (CFRP) Azimuth structure: Steel

26 Frequencies

27 Dome

28 Observing floor

29 CFD Analysis

30 CFD Analysis

31 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

32 NLST