september 19, 2002university of colorado the off-plane option for the reflection grating...

September 19, 2002University of Colorado

The Off-Plane Optionfor the

Reflection Grating Spectrometer

Webster Cash

University of Colorado

September 19, 2002University of Colorado

Chandra Spectra LookLike Traditional GroundSpectra.

Can We Afford to StepBack???

September 19, 2002University of Colorado

Off-plane Mount

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n

In-plane Mount

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September 19, 2002University of Colorado

Radial Groove Gratings

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

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September 19, 2002University of Colorado

An Off-plane X-ray Spectrum

September 19, 2002University of Colorado

Off-plane Tradeoffs

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

CON• Higher Groove Density

PRO

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

September 19, 2002University of Colorado

Throughput•Littrow configuration = = blaze angle - Better Groove Illumination - Maximum efficiency• Constant Graze Angle

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?

September 19, 2002University of Colorado

Raytracing – Arc of Diffraction

September 19, 2002University of Colorado

Raytrace – 35 & 35.07Å

September 19, 2002University of Colorado

Raytracing of Wavelength Pairs and +.07Å

10Å

90Å80Å70Å60Å

50Å40Å35Å30Å

25Å20Å15Å

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

September 19, 2002University of Colorado

Subaperture Effect

September 19, 2002University of Colorado

Grating Modules

R450.0mmInner MirrorsHigh Energy

R151.4mm

Off-plane Grating ModuleLocations on Envelope

R770.0mmOuter MirrorsGrating Area

September 19, 2002University of Colorado

Can Improve Performance

September 19, 2002University of Colorado

Can Improve Performance

September 19, 2002University of Colorado

Raytracing – Arc of Diffraction

September 19, 2002University of Colorado

Raytrace – 35 & 35.028Å

September 19, 2002University of Colorado

Raytracing of Wavelength Pairs and +.028Å

10Å

90Å80Å70Å60Å

50Å40Å35Å30Å

25Å20Å15Å

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

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

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

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

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

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

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

September 19, 2002University of Colorado

Resolution Degradation

1 10 100Grating Resolution (arcsec)

100

1000

10,000

E/

E

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

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

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

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

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

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

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

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.