Wie konstruiert man ein Sonnenteleskop?€¦ · • Desired resolution at 550 nm : 0.1 arcsec – D...
Transcript of Wie konstruiert man ein Sonnenteleskop?€¦ · • Desired resolution at 550 nm : 0.1 arcsec – D...
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GREGORTelescope, AO, BBI
Dirk SoltauKiepenheuer-Institut für Sonnenphysik
CASSDA School, April 20th, 2015
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The demand for high spatial resolution
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Show the simulations the truth?
Courtesy Oskar Steiner, KIS
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Show the simulations the truth?
Solar Tornado
Credits: Wedemeyer-Böhm (2012). Image produced with VAPOR
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High Resolution
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Diffraction Limited Resolution
http://www.olympusmicro.com/primer/anatomy/numaperture.html
Dλθ 22.1=
Example:
λ = 550 nmD = 1 m
θ = 0.67 µrad = 0.14 arcsec
[rad]
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By the way: There is no free lunch
• Number of photons per arcsec2 ∝ T × D2
• Size of the resolution element in arcsec2 ∝ 1/ D2
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Strehl
Strehl > 0.6 „good“Strehl > 0.8 „diffraction limited“
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GREGOR Modulation Transfer Function(MTF)
1“ 0.5“ 0.1“
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Aperture, f-ratio, field of view• Desired resolution at 550 nm : 0.1 arcsec
– D = 1.4 m• Pixel size = 10 µm
– image scale = 0.1 arcsec/20 µm = 5 arcsec/mm– f = 41.2m– f-ratio = f/30
• Number of pixels = 4096– FOV = 200 arcsec
f
1 mm5 arcsec
image scale [arcsec/mm] = ( f[mm] * tan(1“) )-1
= 206270/ f[mm]
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Three types of mirror telescopesNewton Cassegrain Gregory
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Optical Design 1The Simple Solution
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McMath-Pierce, f/54
f=86 m
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McMath-Pierce (Lazy Seven, f/54)
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D = 0.7 mf = 45 m
f/64
Vacuum Tower Telescope (VTT)
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VTT opticallayout
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SOLIS: A solar Cassegrain telescope
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The Gregory Coudé telescope
Picture taken fromhttp://www.irsol.ch/Poster/ao-poster.pdf
D = 0.45 mf = 25 m
f/55
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From Gregory to GREGOR• Has to be shorter than 4 m to fit into dome• Diameter : 1.5 m
• f/# of primary appr. 2• Diffraction limited resolution = 0.08 arcsec
• Central obscuration < 0.3 f/# M2 > 1• Secondary focus F2
FF1F2
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Heat load in a solar telescope focus
• Solar power density (max) 0.1 W/cm2
2
10000ionmagnificatdensity power
≈
fD
Power density in GREGOR F1 ≈ 300 W/cm2 !!
In any solar telescope focus:
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Optical Design
D = 1.5 mf/40
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Power mirrorsRadius of curv. Conic const f/#
M1 -5013 mm -1 f/1.8
M2 -1039 mm -0.306 f/1.2
M3 -2797 mm -0.538 f/4
Foci (FOV = 150 arcsec)f/# Image scale Magn. FOV Power Power dens.
F1 1.8 82 arsec/mm 1.8 mm 1600 W 300 W/cm2
F2 6 23.6 arcsec/mm
3.5 6.3 mm 10 W 30 W/cm2
F3 40 3.6 arcsec/mm 6.6 41.6 mm 4 W 0.3 W/cm2
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Scatter diameter:150 µm = 12 arcsec
Optical quality in F1 (FOV = 200“)
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Scatter diameter:40 µm = 1 arcsec
30 W/cm2
Optical quality in F2 (FOV = 200“)
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Scatter diameter:20 µm = 0.07 arcsec
0.7 W/cm2
Optical quality in F3 (FOV = 200“)
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Overview of telescope structure and optical
path
Dr. Reiner Volkmer, Kiepenheuer Institut für Sonnenphysik, Freiburg
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Dr. Reiner Volkmer, Kiepenheuer Institut für Sonnenphysik, Freiburg 28
Telescope structure
• Sun heats structure and mirrors open telescope and completely foldable dome (telescope in free air flow). Telescopes with 1.5 m free aperture and evacuated light path are very difficult to build
• full performance at wind speeds up to 20 m/s with relative pointing error (rms): 0.5“ (open loop)
• temperature difference to ambient :+0.2 K < ∆T < -0.5 K
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Structure
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Dr. Reiner Volkmer, Kiepenheuer Institut fürSonnenphysik, Freiburg 30
Why Silicon Carbide main mirrors?• solar radiation on surface of 1.5 m main mirror: 2000 W• ∆T mirror – ambient temperature should be < 1K (internal seeing)• heating of mirrors is critical !!!• silicon carbide has high thermal conductivity:
K(silicon carbide) ~ 100 x K(Zerodur) • silicon carbide mirrrors can be "thinned" and structured (high stiffness)
– ► light weight mirror (M1 ~ 90 kg) faster reaction on temperature changes
– ► removal of heat on back side• GREGOR: Primary, secondary and tertiary are silicon carbide mirrors
M336 cm2.5 kg
raw
finished
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Mirror seeing - Mirror Cooling
• Heat transfer bythermal conductivity:
TAd
Q ∆⋅= λ.
Material λ[W/(mK)]
Air 0.03
Glass 0.76
Cesic 121
Zerodur 1.46
Copper 403
d = thicknessA = area
Example M1:ZerodurD = 30 mmA = 1.7 sqm∆T = 3 K dQ/dt = 250 W
Example F1 heat stop:CopperD = 10 mmA = 0.0005 sqm∆T = 10 K dQ/dt = 200 W
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Primary mirror and field stop cooling
Air flowM1 mirror
Nozzle
Heatexchanger
FanHousing
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Thermal control system
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The enemy
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Some atmospheric optics(index of refraction for air)
62 10)22.16.272(1)( −++=
λλn
6106.771)( −=−T
Prn
Wave length dependence of n
T and P –dependence of n
Example : P=1000 mbar, T=293 K → ∆n=10-6 per degree
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Some atmospheric optics(turbulence)
viscosity:scale spatial :d
velocity:vdensity:
η
ρη
ρ dvRe⋅⋅
=
3/11)( −∝ kkE
Reynolds number Re: 105, i.e. . Atmosphere is always turbulent and never laminar
Kolmogorov spectrum
Kolmogorov’s theory of turbuklence
van Gogh, „Starry Night“
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Some atmospheric optics: structure function
[ ] 3/22211 )()( −=−+= rCrnrrnD nrrn
Dn = Structure function Cn2 = structure constant (unit m-2/3 )
Cn2 is a function of height
Cn2 = 10-17 m-2/3
Cn2 = 10-14 m-2/3 37
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D. Soltau, Mai 2000 38
Cn2 profile (Example Hufnagel model)
( )2/120
5
2
),(1500/161000/2
10532
)(15
1
1027
210.2)(
=
+
=
∫
−−−−
km
km
thrhhn
dhhvkm
W
eeeWhhC
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D. Soltau, Mai 2000 39
Fried’s Parameter r0
λπ
β
2
)()sec(423.05/3
0
220
=
=
−
∫
k
dhhCkrL
n
5/60 λ∝r
[ ]223/5
0
2 364.0 radDr
Dtilt
=
λσÜbrigens: Allein die Korrektur für tip/tilt halbiert die durch die Turbulenz verursachte Varianz
r0 is a kind of atmospheric “aperture”
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Measuring r0 (example)
[ ]223/5
0
2 364.0 radDr
Dtilt
=
λσ
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DIMM = „Differential image motion monitor“
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Adaptive Optics: The Idea
• Babcock (1953): The possibility of compensating astronomical seeing
Horace Welcome Babcock, 1912 - 2003
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Adaptive Optics:An Additional Requirement for a
Telescope Design
We need a pupil image
http://lyot.org/background/adaptive_optics.html
Relay Optics
fast
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GREGOR AO System: GAOS
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GAOS: How many actuators do weneed?
Subapertur: 10 cm x 10 cm
r0 = 5 cm
r0 = 10 cm
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How large is the corrected FOV?
Hr0314.0=θ
Example: r0 = 10 cmH = 2 km
θ = 1.6 10-5 rad = 3 arcsec
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Deformable mirror
DM Characteristics•stacked-Piezo, made by CILAS•256 actuators, 196 illuminated•48mm illuminated diameter•5μm stroke•3.2mm actuator pitch•new glueing technology•first resonance frequency > 10 kHz
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CILAS DM: 256 actuators
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Shack Hartmann WFS
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Solar AO• Target: Granulation
– Intrinsiccontrast: 14%
– in telescope 2% bis 5%
– structure sizetypical 2“
Observations mostly done in thevisible and near infrared
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Minimum size of subaperture?
1/arcsec
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taken from ATST archive 52D. Soltau (KIS), Delft Workshop 21./22.02.1321.02.2013
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Bottle neck: The WFS camera
1600 fps
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GREGOR AO GUI
54D. Soltau (KIS), Delft Workshop 21./22.02.1321.02.2013
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Night time AO performance
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Night time performance with AO
FWHM = 0.2 arcsec
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Multi ConjugateAO for GREGOR
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GREGORF1
F2
F3
F4 Pupil
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Back end instruments
• GRIS• GFPI• BBI (Broad Band Imager)
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Instrument Floor
BBIGFPI
GRIS
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Broad Band Imager
F4
F4
WFS
Collim.
Pupil
Pupil
Filter
Cameraf = 260 mm
Detector 1
BS BS
Detector 2
(PCO 4000)PCO Sensicam
Filter(wheel)
f = 400 mm Cameraf = 486 mm
fromtelescope
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Broadband Imager
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First Results - BBI
• June 2013, parallel with Sunrise flight
• Courtesy A. Lagg, R. Schlichenmaier, M. Franz
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Summary
• GREGOR provides world class observingcapabilities. It is:– A large telescope– at an excellent site– fully equipped with AO and backend instruments– beside an excellent Vacuum Tower Telescope
GREGOR�Telescope, AO, BBIThe demand for high spatial resolutionShow the simulations the truth?Show the simulations the truth?High ResolutionDiffraction Limited ResolutionBy the way: There is no free lunchStrehlGREGOR Modulation Transfer Function (MTF)Aperture, f-ratio, field of viewThree types of mirror telescopesOptical Design 1�The Simple SolutionMcMath-Pierce, f/54McMath-Pierce (Lazy Seven, f/54)Vacuum Tower Telescope (VTT)VTT optical layoutSOLIS: A solar Cassegrain telescopeFoliennummer 18The Gregory Coudé telescopeFrom Gregory to GREGORHeat load in a solar telescope focusOptical DesignPower mirrorsOptical quality in F1 (FOV = 200“)Optical quality in F2 (FOV = 200“)Optical quality in F3 (FOV = 200“)Overview of telescope structure and optical pathTelescope structureStructureWhy Silicon Carbide main mirrors?Mirror seeing - Mirror CoolingPrimary mirror and field stop coolingThermal control systemThe enemySome atmospheric optics�(index of refraction for air)Some atmospheric optics�(turbulence)Some atmospheric optics: �structure functionCn2 profile (Example Hufnagel model)Fried’s Parameter r0Measuring r0 (example)DIMM = „Differential image motion monitor“Adaptive Optics: The IdeaAdaptive Optics:�An Additional Requirement for a Telescope DesignGREGOR AO System: GAOSGAOS: How many actuators do we need?How large is the corrected FOV?Deformable mirrorCILAS DM: 256 actuatorsShack Hartmann WFSSolar AOMinimum size of subaperture?Foliennummer 52Bottle neck: The WFS cameraGREGOR AO GUINight time AO performanceNight time performance with AOMulti Conjugate AO for GREGORGREGORBack end instrumentsInstrument FloorBroad Band ImagerBroadband ImagerFoliennummer 63First Results - BBISummary