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Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Science requirements and optimization of the silicon pore
optics design for the Athena mirror
Dick WillingaleUniversity of Leicester
G. Pareschi, F. Christensen, J-W. den Herder, D. Ferreira, A. Jakobsen,
M. Ackermann, M. Collon, M. Bavdaz
SPIE Optics for EUV, X-Ray, and Gamma-Ray Astronomy
VIMontreal 2014 June 27th – 29th
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Specification – Area – Angular Resolution
• Area of 2 m2 at 1 keV– ~5 times larger than the 3 XMM telescopes– sensitivity ~10-17 ergs cm-2 s-1 0.5-2 keV– detect AGN z>6, WHIM…– spectroscopy ΔE~2.5 eV
• Angular resolution 5 arc sec HEW– ~3 times better than XMM telescopes– avoid faint point source confusion– resolve structures like clusters of galaxies– spectral imaging of SNRs, clusters…
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Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Specification – Field of View
• Vignetting and field of view– FOV >40 arc minutes diameter– minimize vignetting– minimize degradation of HEW off-axis– target grasp (collecting area x FOV
product)0.5 m2 deg2 at 1 keV
– deep search for faint sources, AGN…
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Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Si pore optics – XEUS to Athena
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~3 m aperture - focal length F=12m
Si pore module – Cosine Research
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Manufacture of SPO modules
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ESA - Cosine Research
Rib spacing
Axial profile
Kink angle≈R/2F
Axial length L=4Fd/RShort - 20 to 102 mm
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Area of 2 m2 at 1 keV
• 6 sectors – radial arms width 20 mm• Module apertures ~100x50 mm• Radial gaps 10 mm• Azimuthal gaps 14 mm• Inner radius of aperture 258 mm• Outer radius of aperture 1464 mm• Total 972 modules• Inner ring R=285 mm, L=101.9 mm• Outer ring R=1437 mm, L=20.3• F=12 m
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Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Area of 2 m2 at 1 keV
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Lowest curve outer modulesHighest curve inner modules
Black - Ir+B4C overcoatRed - Ir
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Angular resolution 5 arc sec HEW• Conical approximation with F=12 m –> 5.2 arc sec HEW
– Radial pore width d=0.605 mm– Si wafer thickness 0.76 mm – membrane 0.15 mm
• Axial curvature required – mandrel specification– equal on both surfaces d2r/dx2 = -R/16F2 = -θg
2/R– sagittal Δr=0.16 microns inner module, 0.03 microns outer
module• In-plane figure errors – 1 arc sec rms• Out-of-plane figure errors – 1 arc sec rms but unimportant• Focal length errors (kink angle error) – 1 mm rms (F=12 m)• Module alignment
– Rotation about optical axis 2 arc sec rms– Shift in aperture plane 0.05 mm rms– Tilt errors 1 arc minute rms
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Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Vignetting – off-axis area
• In-plane vignetting– Radial pore size d
(fixed)– Length of pores L– Drops to zero at
θ≈d/2L
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• Out-of-plane vignetting– Rib spacing drib
– Length of pores L– Drops to zero at
θ≈drib/2L
Ray tracing of a single module
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Field of view vs. drib for Athena
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drib 1, 2, 3, 4, 5 mm FOV at half on-axis area 1 keV
Ray tracing full aperture
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
FOV, Photon Energy, Grasp – drib 3mm
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Grasp 0.5 m2 deg2 at 1 keV for FOV 40 arc mins
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Angular resolution off-axis• Wolter I - principal plane (join plane) flat
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• Wolter-Schwarzschild (W-S) Obeys Abbé sine condition– principal plane spherical radius curvature F
• To implement W-S is simpleChange θg - kink angle between 1st and 2nd surfaces in
moduleMount modules on the correct spherical surface
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Using W-S Principal Plane
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Black – Wolter/conical
Green – W-S/conical
Blue – Wolter
Red – W-S
Dotted – W-S limit no errors
Error budget – 5 arc sec HEW
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Angular resolution off-axis
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Split curvature between 1st and 2nd surfacesKeep curvature sum constant – on-axis HEW remains constant
- θg2/R 1st and 2nd 1st -2 θg
2/R, 2nd conical
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Angular resolution off-axis
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Split curvature between1st and 2nd surfaces
Solid black conical-conicalSolid red Wolter
Solid green curveclose to optimumconical 1st surface-2 θg
2/R 2nd surfaceAverage HEW5.6 arc sec 40 arc min FOV5.9 arc sec 50 arc min FOV
Use W-S principal plane
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
Conclusions• Area 2 m2 at 1 keV
– 3 m aperture F=12m– ~970 SPO modules– Ir coating
• Angular resolution 5 arc seconds HEW on-axis– axial curvature -2 θg
2/R sum over 1st and 2nd surface
– tight but achievable error budget• Minimize vignetting
– rib spacing 3 mm– grasp 0.5 m2 deg2 at 1 keV 40 arc min FOV
• Minimize degradation of angular resolution off-axis– W-S principal plane – change kink angle within
modules– Curvature 1st conical 2nd -2 θg
2/R– Mean HEW 5.6 arc sec for 40 arc min FOV 16
Optimization of the SPO Design for the Athena MirrorDick Willingale et al. – SPIE August 2014
The End
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