The Off-Plane Option for the Reflection Grating Spectrometer

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The Off-Plane Optionfor theReflection Grating
Spectrometer

• Randy McEntaffer
• Webster Cash, Steve Osterman,
• Ann Shipley, Brian Gleeson
• University of Colorado

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Off-plane Mount
In-plane Mount
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Radial Groove Gratings
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Off-plane Grating ModuleLocations on Envelope
R450.0mm Inner Mirrors High Energy
Grating Modules
R770.0mm Outer Mirrors Grating Area
R151.4mm
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Off-plane Tradeoffs
CON
PRO

• Higher Groove Density

• Higher Throughput
• Higher Resolution
• Better Packing Geometry
• Looser Alignment Tolerances

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Raytracing Arc of Diffraction
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Raytrace 35 35.028Å
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Resolution
Primary Response
lt35 Response
Extended CCD
ASSUMPTIONS 5500g/mm 15 SXT 2 gratings 2
alignment
Calorimeter 2eV
Mission Goal
I-P n1
Mission Requirement
I-P n2
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Effective Area
5000
ASSUMPTIONS Coverage 40 of outer
envelope Off-Plane Groove Efficiency 80 of
theoretical 85 Structure Transmission CCD thin
Al filter only

• Goal

4000
off-plane
3000
cm2
2000
baseline
1000
Mission Requirement
0
0.1
1.0
10.0
Energy (keV)
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Off-Plane Program

• Optical Design Projected Performance
• Looks Attractive
• Engineering Requirements
• Has Significant Advantages
• Grating Suppliers
• Several Possible Suppliers
• Holographic Techniques Look Better Than
  Mechanical
• Grating Efficiency
• Test Gratings at Colorado Now
• Resolution Demonstration
• Scheduled this Summer at Colorado
• TRL Development
• Plan to Achieve TRL 6

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Grating Test Facility at CU

• Used for COS and FUSE

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Grating 1

• Jobin-Yvon, radial grooves, 4246 g/mm, unblazed

_at_ ? 2º Absolute Efficiency strongest order
13 Sum orders 29
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Grating 2

• Jobin-Yvon, radial grooves, 4246 g/mm, blazed 13º

_at_ ? 2º Absolute Efficiency strongest order
6.4 Sum orders 11 30 (w/
scatter)
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Grating 3
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Grating 3

• MIT, parallel rulings, 5000 g/mm, blazed 7º

Groove eff. Abs. eff./Reflectivity (a.k.a.
Relative eff.)
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Conclusion

• Off-plane can significantly improve performance
  of Constellation-X RGS
• Gratings can be built to required efficiency and
  scatter specifications
• Resolution tests to be conducted this summer