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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