use of fel off-axis zone plate spectrometer to measure relative k by the pinhole/centroid method

R. M. [email protected] November 14, 2005

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LCLS Beam-Based Undulator K

Measurements Workshop

Use of FEL Off-Axis Zone Plate Spectrometer to measure relative K by the Pinhole/Centroid method

LCLS Beam-Based Undulator K Measurements Workshop

November 14, 2005


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Baseline Diagnostics

SolidAttenuator

Gas Attenuator

High-EnergySlit

Start of Experimental

Hutches

5 mm diameter

collimators

Muon Shield

FEL Offset mirror

system

TotalEnergy

CalorimeterWFOV Direct

Imager

Scanning Spectrometer / Indirect Imager

mirrors

Windowless Ion

Chamber

Windowless Ion

Chamber

e-

Diagnostic Package

NFOV Direct Imager

FEL Spectrometer and Direct Imager in 2nd Hutch of NEH


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8.26 keV Transmission Grating

31021

NE

E

P = 200 nmN = 500

D = 100 m

Sputter-sliced SiC / B4C multilayer

33 m thick

Beam100 m

Interference Function

Single Slit Diffraction Pattern

Observed Intensity

angle

mDP

3750

mD 5


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Sputter-Sliced SiC/B4C Grating

SiCB4C


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Sputtered-sliced multilayer gratings as high bw Sputtered-sliced multilayer gratings as high bw spectrometersspectrometers

5-m-thick Mo/Si multilayer (d=200 Å) on Si wafer substrate. Thinned and polished to a 10- m-thick slice

SEM image of Mo/Si multilayer


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Parabolic wave calculation shows > 10 nm thick gratings with 2 nm

periods do not work

diffraction peaks in far-field no diffraction peaks in far-field

2 nm period

10 nm2 nm

period

50 nm


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Long grating acts like a coupled waveguide

10 nm long grating shows some cross coupling in near-field

50 nm (or longer) shows complete cross coupling in

near-field

Parabolic wave calculations by Jeffrey S. Kallman


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200 nm period x 33 microns works

diffraction peaks in far-field

200 nm period

33 m

Waveguide coupling limits us to periods > 200 nm


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Spectrometer location in FEE to measure Spontaneous Radiation

Thick Slit

Be mirrors1 & 2

Attenuators

SiC Mirror 1

Put camera here

SiC Mirror 2

5 mm dia. Collimator 1

2.5 m DiagnosticsPackage Contains Grating and Variable Slit


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Position of Spontaneous Spectrometer

Optic Camera

5 m


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FEE Schematic with Transmission Grating Spectrometer

SolidAttenuator

Gas Attenuator

ThickSlit

Start of Experimental

Hutches

5 mm diameter

collimators

Muon Shield

FEL Offset mirrors

Grating

WFOV Direct Imager

Spectrometer Imager

Windowless gas

detectors

Variable Slit

e-

Diagnostic Package


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1st Order DiffractionPeaks

4 mm

FEL Transmission Grating Spectrometer

Thick Slit5 cm Ta

capped with 1 cm B4C

YAG Scintillator50 microns thick

Thin Adjustable Slit1 mm Ta

Very high energy photons go through everything

50-100 micron1 mm

6 m

TransmissionGrating200 nm Period100 micron Aperture

5 m


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Monte Carlo Generation of Photons from Near-Field

CalculationsPhotons are aimed at Sven’s near field distributions…

… but allowed to reflect off of the vacuum pipe or get absorbed in the breaks

Slits, gratings and scintillator placed in beam


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Grating

P = 200 nm

Number of P = 500

Distance = 5 m

8.26 keV FEL Only

10000 photons

FEL ~ 160 m FWHM


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Diffracted angle micro R

Diffraction angle, 4,0002,0000-2,000-4,000

Events

/ 1

00

2,200

2,000

1,800

1,600

1,400

1,200

1,000

800

600

400

200

0

Simulated Scattering angle for photons through grating

Rad


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5 m downstream of grating

Final XY zomm in

Final x, mm54.543.532.521.510.50-0.5-1-1.5-2-2.5-3-3.5-4-4.5

Fin

al y

, mm

5

4

3

2

1

0

-1

-2

-3

-4


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Shadow of optic defines center

Final XY double zoom

Final x, micron2001000-100

Fin

al y

, mic

ron

200

100

0

-100


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First order peaks are 100 microns across for FEL

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y

, mic

ron

4,400

4,200

4,000

3,800

3,600

Distance E/E

/P*f 3750 m 1

Pixel Size 10 m 2.7x10-3

1/N 7.5 m 2x10-3

Aperture 100 m 2.7x10-2


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Off-Axis Zone Plate Spectrometer

Zone plate axis

Beam Axis

l > l0

l < l0

l = l0


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Off-Axis Zone plateFocal Length 4.643 m

Offset 3750 microns

50 and 100 m aperture

Distance = 5 m

Starting Zone 20204, 185 nm

Ending Zone 21296, 181 nm

8.26 keV FEL Only

10000 photons

FEL ~ 160 m FWHM


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Scintillator Image

Final XY zomm in

Final x, mm543210-1-2-3-4

Fin

al y

, mm

4

2

0

-2

-4

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y

, mic

ron

4,400

4,200

4,000

3,800

3,600

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y

, m

icro

n -3,600

-3,800

-4,000

-4,200

-4,400

Positive

Negative


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Scintillator Image around 5% Bw

Resolution is 2.36*4.8 microns/4092 microns = 3 x 10-3 = 23 eV

Spectra 5% bw

Final y, micron-4,050-4,100-4,150-4,200

Eve

nts

/ 2 m

icro

n

30

25

20

15

10

5

0


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50 micron aperture diffraction

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Eve

nts

/ 2 m

icro

n

20

15

10

5

0

Resolution is 2.36*7.9 microns/4092 microns = 5 x 10-3 = 38 eV


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Wavelength calibration

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Eve

nts

/ 2 m

icro

n

30

25

20

15

10

5

0

= 0.149942 nm

= -4091 m

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Eve

nts

/ 2 m

icro

n

30

25

20

15

10

5

0

= 0.151113 nm

= -4124 m


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First Undulator Segment

1st undulator segment emits

Thick slit 1 mm wide

1 x 1 mm single undulator distribution simulated from 7.5 to 8.5 keV

Thin slits forming crossed 100 m apertures in x and y


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Initial photon position and energyFirst Segment

Initial Z

z, meter200150100500

Eve

nts

/ 2 m

eter

5,000,000

4,000,000

3,000,000

2,000,000

1,000,000

0

Source Energy Distribution

E, KeV8

Eve

nts

/ 0.0

05 K

eV

600,000

500,000

400,000

300,000

200,000

100,000

0


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Zero order peak, First Segment



Fin

al y

, m

icro

n

200

100

0

-100


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Area near first order

First Segment

Final XY zomm in

Final x, mm543210-1-2-3-4

Fin

al y

, mm

4

2

0

-2

-4

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y

, mic

ron

4,400

4,200

4,000

3,800

3,600

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y

, mic

ron

-3,600

-3,800

-4,000

-4,200

-4,400


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First Segment Normalization

• Sven’s near-field calculation– 2 x 2 mm

– 8.0 to 8.5 keV

– 79 nC

– 0.034 J

– 2.553 x 107 Photons

• Simulation– 107 Photons simulated

– 31 nC

• Scale Monte Carlo by x 2.553 for full pulse


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Spectra of nominal First Segment

1403 photons in simulation

=> 3600 ± 100 in a 79 nC pulse

Fitted centroid: = - 4088.81 ± 0.07

m

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Events

/ 2

mic

ron 80

60

40

20

0

Need at least x 200 more photons!


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Spectra of First Segment Detuned by 10-3


=> 3600 ± 100 in a 79 nC pulse


m

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Eve

nts

/ 2 m

icro

n 80

60

40

20

0


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Spectra of First Segment Detuned by 10-4


=> 3700 ± 100 in a 79 nC pulse


m

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Even

ts / 2

mic

ron 80

60

40

20

0


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Last Undulator Segment

Last undulator segment emits

Thick slit 1 mm wide

Thin slits forming crossed 42 m apertures in x and y

1 x 1 mm single undulator distribution simulated from 7.5 to 8.5 keV


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Initial photon position and energy

Source Energy Distribution

E, KeV8

Eve

nts

/ 0.

005

KeV

500,000

400,000

300,000

200,000

100,000

0

Initial Z

z, meter150100500

Even

ts /

2 m

eter

5,000,000

4,000,000

3,000,000

2,000,000

1,000,000

0

Last Segment


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Zero order peak, Last Segment



Fin

al y

, m

icro

n200

100

0

-100


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Area near first order

Final XY zomm in

Final x, mm543210-1-2-3-4

Fin

al y

, m

m

4

2

0

-2

-4

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y

, m

icro

n

4,400

4,200

4,000

3,800

3,600

Spectra

Final x, micron4,0002,0000-2,000-4,000

Fin

al y,

mic

ron

-3,600

-3,800

-4,000

-4,200

-4,400

Last Segment


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Spectra of nominal Last Segment

Spectra 5% bw

Final y, micron-4,050-4,100-4,150-4,200

Eve

nts

/ 2

mic

ron

25

20

15

10

5

0


=> 3300 ± 200 in a 79 nC pulse


m


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Last Segment Normalization

• Sven’s near-field calculation– 2 x 2 mm– 8.0 to 8.5 keV– 79 nC– 0.1437 J– 1.090 x 108 Photons

• Simulation– 107 Photons simulated – 7.2 nC

• Scale Monte Carlo by x 10.9 for full pulse


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Spectral Measurements Summary

Fit Centroid

m

Spectral Shift, E/E

From Last Nominal

x 10 -4

From First Nominal

x 10 -4

Last Nominal - 4088.0 ± 0.3 0 ± 1 -2.0 ± 0.8

First Nominal - 4088.81 ± 0.07 2.0 ± 0.8 0.0 ± 0.2

First detuned 10-3

- 4095.87 ± 0.07 19.3 ± 0.8 17.3 ± 0.2

First detuned 10-4

- 4089.19 ± 0.07 2.9 ± 0.8 0.9 ± 0.2

K

K

K

K

K

K

7.1

22

2

2

1


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Expected variations in 1

u

K

2

2

1 2

21K

K

7.1

1

e

e

T

T

2

1

On axis: Effect of changing K But


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Simulation of Last segment full spectra, full angular distribution

Source Energy distribution

E, KeV1050

Even

ts /

0.1

KeV

35,000

30,000

25,000

20,000

15,000

10,000

5,000

0


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Last Segment Full Field Normalization

• Sven’s near-field calculation– 120 x 40 mm– 0.0 to 24687.8 keV– 79 nC– 0.4845 J– 5.274 x 1010 Photons

• Simulation– 107 Photons simulated – 0.015 nC

• Scale Monte Carlo by x 5274 for full pulse


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Observed in scintillator, Last segment, full field

Final XY

Final x, mm3020100-10-20

Fin

al y

, mm

30

20

10

0

-10

-20

Final XY zomm in

Final x, mm543210-1-2-3-4

Fin

al y

, mm

4

2

0

-2

-4

One simulated photon = 5274 real photonsWe expect a signal of 3300 real photons here


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Thin scintillator reduces background by x 7 ± 3

Spectra 5% bw

Final y, micron-4,000-4,100-4,200

Events

/ 2

mic

ron

1

0.8

0.6

0.4

0.2

0

Spectra in Scintillator

Final y, micron-4,000-4,100-4,200

Eve

nts

/ 2 m

icro

n

1

0.8

0.6

0.4

0.2

0

All photons7 photons in simulation37000 ± 14000 in a 79 nC pulse

Photons stopping in scintillator1 photons in simulation5300 ± 5300 in a 79 nC pulse

Conclude backgrounds of 5300 ± 5300 in a 79 nC pulse


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Summary

• Investigated 100 micron aperture FEL Transmission Grating for use in measuring K

• Sensitivities are roughly at the limit of what is needed

• Signal level is too low by at least a factor of 200. • More aperture, say 1.4 x 1.4 mm would help. Larger

focal distance would allow larger periods• Signal:Backgrounds with thin scintillator are at least

1:1• Beam stability and pointing (relative to the 100

micron aperture) will be an issue that is not investigated here


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Monte Carlo used for design of Single Shot 30-70 keV Spectrometer

50

60

70

80

90

100

110

0 100 200 300 400 500

Pxl distance

Sm K40.1 keV

Sm K45.4 keV

E1E2

No filter

25 m Sm filter

Straight-thru bkg

W/SiC bilayers

d = 2 nm

B=0.45 deg

Reflectivity @40 keV > 90% LCLS Monte-

Carlo Simulation

use of fel off-axis zone plate spectrometer to measure relative k by the pinhole/centroid method

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