September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating...
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![Page 1: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/1.jpg)
September 19, 2002University of Colorado
The Off-Plane Optionfor the
Reflection Grating Spectrometer
Webster Cash
University of Colorado
![Page 2: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/2.jpg)
September 19, 2002University of Colorado
Chandra Spectra LookLike Traditional GroundSpectra.
Can We Afford to StepBack???
![Page 3: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/3.jpg)
September 19, 2002University of Colorado
Off-plane Mount
sinsinsin
d
n
In-plane Mount
d
n sinsin
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September 19, 2002University of Colorado
Radial Groove Gratings
![Page 5: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/5.jpg)
September 19, 2002University of Colorado
Off-plane Resolution
At typical values of off-plane angles and 15” telescope resolutionR ~ several hundred → thousand
Sub-Aperturing improves it further
cos
sinsinsin
BR
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September 19, 2002University of Colorado
An Off-plane X-ray Spectrum
![Page 7: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/7.jpg)
September 19, 2002University of Colorado
Off-plane Tradeoffs
• Higher Throughput• Higher Resolution• Better Packing Geometry• Looser Alignment Tolerances
CON• Higher Groove Density
PRO
![Page 8: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/8.jpg)
September 19, 2002University of Colorado
Packing Geometry
+1
0
Central grating must be removed.Half the light goes through.
+1
0
Gratings may be packed optimally
In-plane
Off-plane
![Page 9: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/9.jpg)
September 19, 2002University of Colorado
Throughput•Littrow configuration = = blaze angle - Better Groove Illumination - Maximum efficiency• Constant Graze Angle
![Page 10: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/10.jpg)
September 19, 2002University of Colorado
Holographic Gratings
Last year we reviewed approaches to fabricatinghigh density gratings.
At Jobin-Yvon (outside Paris)Create rulings using interference pattern in resistIon-Etch Master to Create Blaze
Radial Geometry – Type 4 Aberrated BeamsDensity: Up to 5800 g/mm Triangular (<35 deg blaze)
In UV holographic blazed gratings have very low scatterand good efficiency – same in x-ray?
![Page 11: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/11.jpg)
September 19, 2002University of Colorado
Raytracing – Arc of Diffraction
![Page 12: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/12.jpg)
September 19, 2002University of Colorado
Raytrace – 35 & 35.07Å
![Page 13: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/13.jpg)
September 19, 2002University of Colorado
Raytracing of Wavelength Pairs and +.07Å
10Å
90Å80Å70Å60Å
50Å40Å35Å30Å
25Å20Å15Å
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September 19, 2002University of Colorado
Internal Structure of Telescope
Blur Favors Dispersion in Off-plane DirectionSpectral line of HeII 304Å
displaying In-plane scatter
Data from a radial grating in the
off-plane mount, Wilkinson
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September 19, 2002University of Colorado
Subaperture Effect
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September 19, 2002University of Colorado
Grating Modules
R450.0mmInner MirrorsHigh Energy
R151.4mm
Off-plane Grating ModuleLocations on Envelope
R770.0mmOuter MirrorsGrating Area
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September 19, 2002University of Colorado
Can Improve Performance
![Page 18: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/18.jpg)
September 19, 2002University of Colorado
Can Improve Performance
![Page 19: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/19.jpg)
September 19, 2002University of Colorado
Raytracing – Arc of Diffraction
![Page 20: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/20.jpg)
September 19, 2002University of Colorado
Raytrace – 35 & 35.028Å
![Page 21: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/21.jpg)
September 19, 2002University of Colorado
Raytracing of Wavelength Pairs and +.028Å
10Å
90Å80Å70Å60Å
50Å40Å35Å30Å
25Å20Å15Å
![Page 22: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/22.jpg)
September 19, 2002University of Colorado
Resolution
0.1 1.0 10.0Energy (keV)
100
1000
10,000
E/
E Calorim
eter –
2eV
I-P n=1
I-P n=2
Primary Response
ASSUMPTIONS:5500g/mm15” SXT2” gratings2” alignment
<35% ResponseExtended CCD
Mission Requirement
Mission Goal
O-P n=1
O-P n=2
O-P n=3
MissionRequirement
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September 19, 2002University of Colorado
Effective Area
Energy (keV)
cm2
ASSUMPTIONS:
Coverage 40% of outer envelope
Off-Plane Groove Efficiency 80% of theoretical
85% Structure Transmission
CCD thin Al filter only
0.1 1.0 10.00
5000
off-plane
1000
2000
3000
4000
baseline
Goal
Mission Requirement
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September 19, 2002University of Colorado0.1 1.0 10.0
Energy (keV)
15
area
x r
esol
utio
n ÷
106
off-plane
0
5
10
20
in-plane
calorimeter
Figure of Merit
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September 19, 2002University of Colorado0.1 1.0 10.0
Energy (keV)
15
area
x r
esol
utio
n/E
(kev
)/ 1
06 off-plane – R~3000
0
5
10
20
in-plane
calorimeter
Figure of Merit with Spectral Weighting
off-plane – R~1500
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September 19, 2002University of Colorado
Pros & Cons of Off-plane vs. Baseline Design
● Pro:
– Greater Resolution from Sub-aperturing
– Greater Collecting Area – higher groove efficiency
– Less Sensitivity to Grating Alignment
– Less Sensitivity to Grating Flatness
– Lower scatter in Dispersion Direction
– Fewer Gratings Required
– Thicker Substrates Acceptable
– Smaller Structure Required
● Con:
– Higher groove density required
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September 19, 2002University of Colorado
Difficulties of High Resolution (/Δ>1200)
• flatter gratings• tighter alignment• tighter focus• telescope depth of focus adjustment• zero order monitor essential to aspect solution• more difficult calibration• greater astigmatism
– higher background– more source overlap
![Page 28: September 19, 2002University of Colorado The Off-Plane Option for the Reflection Grating Spectrometer Webster Cash University of Colorado.](https://reader031.fdocuments.in/reader031/viewer/2022032523/56649d825503460f94a66f3b/html5/thumbnails/28.jpg)
September 19, 2002University of Colorado
Depth of Field Problem
Solutions for Study:Smaller GratingsCurved GratingsAdjust Telescope Segments
Hope that it ismerely a matter ofmounting existing shellsat different radii
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September 19, 2002University of Colorado
Resolution Degradation
1 10 100Grating Resolution (arcsec)
100
1000
10,000
E/
E
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September 19, 2002University of Colorado
Off-plane Grating Module
22cmGrating size:10cm x 10cm x 0.2cmGraze angle: 2.7o
GratingsQty. 20
11cm
11cm
Holder
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September 19, 2002University of Colorado
Off-plane Grating Resolution Options
~ 1000 ~ 5000
• SXA (Al/SiC) substrates
• Easy tolerances
• Simple mount
• No thermal gradient
• Mass OK
• Glass/Si substrates?
• More difficult tolerances
• More difficult mount
• Probable thermal gradient issues
• Mass constraint more difficult to meet
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September 19, 2002University of Colorado
Off-plane Grating Estimated Tolerances
Error type Zero-order Allowable Tolerances
Equation = 15 arcsec = 2 arcsec
Surface error 36.5m 4.9m
x 36.5m 4.9m
y 1mm 1mm
z 775m 103m
x 11.5° 11.5°
y 0.75 arcsec 0.1 arcsec
z 31.8 arcsec 4.2 arcsec
20
s
cos20
sx
10
wy
sin20
sz
h
w
5sin
20
sin10
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September 19, 2002University of Colorado
Off-plane Grating Module Estimated Mass
Materials Gratings (Kg)
Holder (Kg)
Light-weight
One Module
(Kg)
Qty Modules
Total mass
(Kg)
SXA/SXA 1.16 1.20 none 2.36 32 75.65
SXA/SXA 1.16 1.20 25% 2.17 32 69.53
SXA/6061 1.16 1.11 none 2.27 32 72.73
FS/Invar/Ti 0.88 1.568 70% 2.45 32 78.36
FS/Titanium 0.88 1.488 30% 2.37 32 75.82
FS/GrEp/Invar 0.88 1.687 none 2.57 32 82.17
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September 19, 2002University of Colorado
Wavefront Error: Resolution 1000
Total allowable error 21 m
Spare 8.054(rss)
Fabrication2.87m
(rss)
Mount 10 um (WAG)
Test(/50)
.013 m
Stability6.23m
(rss)
Alignment10 m
(estimate)
1g Sag.09 m (calc)
Temp (bulk)±2.5°C
2.02 m (rss)
Substrate Figure(3)
1.9m (requirement)
ReplicationEpoxy cure strain
1.0 m (calc)
Replicate Separation Strain
1.9 m(WAG/3)
Creep0.5 m (WAG) Water absorption
(assume 0.3%) 1.6m(calc)Thermal gradient
(0.5°C) 6 m (calc) Jitter (on orbit)
.0003 m (WAG/calc)
Mount 2 m(WAG)
Reflective coatingbimetallic effect
0.3 m (calc)
Replication epoxybimetallic effect
0.0005 m(calc)
Constellation X Off-plane Grating Mount rms Wavefront Error Budget (15 arcsec max)All errors are presented as rms wavefront error
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September 19, 2002University of Colorado
Wavefront Error: Resolution 5000
Total allowable error 2.77 mm
Spare 0.754 m
(rss)
Fabrication1.16 m
(rss)
Mount 1.5 m (WAG)
Test(50)
.013 mm
Stability0.62 m
(rss)
Alignment1.75 m (estimate)
1g Sag.11 m (calc)
Temp (bulk)±2.5°C
0.21 m (rss)
Substrate Figure(1.5)
0.95 m (requirement)
ReplicationEpoxy cure strain
0.23 m (calc)
Replicate Separation Strain
0.6 m(WAG/1)
Creep0.1 m (WAG) Water absorption
(assume 0.3%) 0.35 m
(calc)Thermal gradient(0.1°C) 0.5 m
(WAG/calc) Jitter (on orbit).0003 m
(WAG/calc)
Mount 0.2m(WAG)
Reflective coatingbimetallic effect
.07 m (calc)
Replication epoxybimetallic effect
0.008 m(calc)
Constellation X Off-plane Grating Mount rms Wavefront Error Budget (2 arcsec max)All errors are presented as rms wavefront error
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September 19, 2002University of Colorado
Off-plane Grating Prototype: steps and schedule
Phase Task Leadtime
1 Preliminary feasiblility study of type 4 aberration corrected grating distribution to approximate radial distribution
4-5 mos.
(Jun ‘02 to ~Oct ‘02)
2 Preliminary study of blaze process using existing masks (30o profile goal).
(work done in parallel with step 1)
4-5 mos.
(Jun ‘02 to ~Oct ‘02)
3 Contingent upon step 1&2 positive result.
Deliverable: 58x58x10mm parallel groove sample with 30o blaze angle.
4 mos.
(Oct ‘02 to ~Feb ‘03)
4 Contingent upon positive test of sample.
Deliverable: 58x58x10mm radial groove distribution with blazed profile.
3 mos.
(Mar ‘03 to ~Jun ‘03)
5 Ray-tracing to optimize recording configuration
Deliverable: 120mm square radial distribuation with blazed profile and flight groove density.
TBD
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September 19, 2002University of Colorado
In Conclusion, Off-plane Can:● Match RGS to Calorimeter Scientifically
– R~1500 – greatly eased tolerances
● or Significantly Enhance Con-X Science– R~3000– tolerances at currently expected levels
Study funded by the Con-X project. First results in January.