Generating X-rays and EUV radiation at ASTA Tanaji Sen March 5, - - PowerPoint PPT Presentation

Generating X-rays and EUV radiation at ASTA

Tanaji Sen March 5, 2015

Outline

• Channeling Radiation
• Parametric X-rays (PXR)
• PXR while channeling
• Phase contrast imaging
• X-rays and EUV with nanostructures
• T. Sen

X-arys and EUV at ASTA 2

Goals of X-ray generation

• Create a source of brilliant, monochromatic

and tunable X-rays. Increase spectral brightness by orders of magnitude

• Use the X-rays for applications; especially

phase contrast imaging

• Establish ASTA as a model for a compact X-ray

source with X-band linacs

• Establish ASTA as a user facility based on

applications

• T. Sen

X-arys and EUV at ASTA 3

Radiation sources for X-rays

• Channeling radiation
• Parametric radiation
• Compton Scattering
• Transition radiation
• Synchrotron radiation
• Coherent Bremsstrahlung, ----

10 keV X-rays

• T. Sen

X-arys and EUV at ASTA 4

Source Beam Energy Synchrotron Radiation Transition Radiation Compton Scattering Channeling Radiation Parametric Radiation 3 GeV 300 MeV 22 MeV ~ 10 MeV 5.7 MeV

Channeling Radiation

Particles are channeled within a critical angle Energy of X-rays EX ~ 2γ2(𝜁𝑗 − 𝜁𝑔)/(1+ γ2 θ2 ) QM needed for 𝐹𝑓< 100 MeV For planar channeling, eigenvalues 𝜁 found by solving 1D Schrodinger’s equation using the Doyle-Turner form of the atomic potential

• T. Sen

X-arys and EUV at ASTA 5

Crystal planes

• (110) plane has a deeper potential than (100), higher

energy X-rays

• (111) plane has more bound states, broader X-ray spectrum
• Preferred plane is (110)

(110) plane

(100) plane (111) plane

• T. Sen

X-arys and EUV at ASTA 6

Photon Yields

• Radiative transitions : apply Fermi’s golden rule

Selection rule: transitions only between states of

• pposite parity, |m-n| = Odd
• Non-radiative transitions, mainly inelastic thermal

scattering off lattice vibrations, determine population Pn(z)

• Approximate selection rule: |m-n| = Even
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Photon Angular Distribution

J.U. Andersen et al, (1983)

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Dipole moment Photon absorption Population in nth state Lorentzian line shape

Line Width

• Intrinsic line width from finite lifetime of channeling states
• Bloch wave broadening from finite width of energy bands,
• Multiple scattering: scattering in planar channels weaker than in

amorphous media

• Energy spread of electron beam
• Detector resolution
• T. Sen

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Experiment at ELBE (2007)

• Observed CR at beam energies

from 14.6 MeV to 30 MeV

• Beam current ~ 100 nA
• Transverse emittance = 3μm

Wagner et al (2007) Now in ASTA beamline

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FZDR, Rossendorf, Germany

ELBE Measurements & Simulations

Energy [MeV] Thickness [μm] Exp yield [phot/sr-e]

• Theor. Yield

[phot/sr-e] Exp/Theor 14.6 42.5 168 0.048 0.090 0.11 0.22 0.45 0.41 17 42.5 168 0.059 0.13 0.15 0.29 0.39 0.45 25 42.5 0.16 0.32 0.50 30 42.5 168 0.23 0.52 0.45 0.89 0.51 0.59

Azadegan (2007)

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Dechanneling

• T. Sen

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Dechanneling Model

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Rechanneling, Yield Saturation

Yield saturates beyond ~7 Locc

• T. Sen

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Improvements to Model

• Introduced heuristic dechanneling model
• Corrected potential VI for thermal scattering;

affects transition rate between states

• Include effects of a finite beam divergence
• Inclusion of linewidth contributions from

multiple scattering, Bloch wave broadening

• Correction to the line shape in the intensity

spectrum

• Not included: electron-atomic electron

scattering contribution to linewidth

• T. Sen

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Updated ELBE calculations

• Theory bounds for

42.5/168/500 μm

• Lower line : dechanneling

from 1st/7th /14th free state and above.

• Upper line: dechanneling

from 3rd /9th / 15th free state and above

• Importance of

rechanneling (free state to bound state) for thicker crystals

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ASTA parameters

Parameter Value Beam energy Bunch charge Bunch frequency Average beam current Transverse emittance Bunch length Energy spread Crystal, plane Critical angle 20 – 50 MeV ~ 20 pC (low charge operation) 3 MHz 300 nA < 100 nm 3 ps < 1% Diamond, (110) 1.5 mrad(20 MeV), 1mrad(50MeV)

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Real and Imaginary Potentials

20 MeV 50 MeV

• Depth of real potential about 24 eV
• Energy bands differ by few eV in rest

frame, transform to 10’s of keV in lab frame

• Corrected imaginary potential is

weaker, reduces non-radiative transition rates, reduces intrinsic line widths

• T. Sen

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Intensity spectra

20 MeV, 42.5 μm 20 MeV, 168 μm 50 MeV, 42.5 μm 50 MeV, 168 μm

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Brilliance at ASTA

𝐂𝐎 = 𝐞𝟑 𝐎 𝐞𝛛𝐞𝛁 𝐉𝐛𝐰 𝐟 𝛅𝟑(𝝉′𝒇)𝟑𝐅𝑌 𝐅𝐬𝐠[ 𝜄𝐷 𝟑𝝉′𝒇 ] 𝟐𝟏−𝟒 𝛝𝐎𝟑 photons 𝑡 − mm − mrad 2 − 0.1% BW

• T. Sen

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Increasing the brilliance

• Expected brilliance with 100nm

about 104 x ELBE

• Field emitter nanotip cathode :

emittance ~ 10nm

• Tested at A0-HBESL
• Brilliance would increase by

~100

• Thicker crystals may help
• T. Sen

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• P. Piot et al (2014)

ASTA Channeling Experiments

• Initial studies will look at CR dependence on electron beam

parameters: energy, bunch charge, emittance, spot size, energy

• spread. Operate initially with low bunch charge (~ 20 pC), fewer

bunches.

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Channeling Summary

• Updated model results in better agreement with

measurements at ELBE.

• Yields agree within 15%, linewidth to a factor of 2 because
• f neglecting e- <-> atomic e- scattering
• Occupation length & rechanneling increase with thickness,

but insensitive to particle energy.

• Yield saturates at ~ 7x Occupation length for 1-> 0

transition.

• ASTA 50 MeV beam: 142 keV from 1-> 0, 89 keV from 2-> 1
• transition. Linewidth around 14%
• Expected brilliance ~ 3x1010 phot/(s-(mm-mrad)2-0.1% BW)

with transverse emittance 100nm, crystal t=168 μm

• Field emitter cathodes could increase brilliance another

100 times

• T. Sen

X-arys and EUV at ASTA 23

Parametric X-Rays

• Phase difference =

𝑒(1

𝛾−𝑜 𝑑𝑝𝑡𝜄𝐸)

sin𝜄𝐶 𝑑

𝜕 = 2𝜌𝑛

• Constructive interference of virtual photons around

𝜄𝐸= 2𝜄𝐶

• PXR photon energy at this angle 𝐹 = 𝑛ℏ𝑑τ/(2𝑡𝑗𝑜𝜄𝐶)
• Independent of electron beam energy

M.L. Ter-Mikaelian, V. Baryshevsky (1970s)

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PXR Features

• Emitted at large angles from the beam direction.

Differentiates it from channeling, bremsstrahlung

• X-ray energy is independent of beam energy
• Tunable by changing crystal orientation
• Narrow line width. Typically ~ 1%
• Photon energy depends on detection angle (spatial

dispersion); collimation further reduces energy spread

• Lower intensity than channeling radiation
• Lower background from other sources, especially at

large angles.

• Similar angular spectrum as transition radiation
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Crystal Geometries

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Spectral Angular Distribution

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Spectral angular distribution - 2

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PXR with 8 MeV beam

• Angular distribution similar to transition radiation.

Minimum at the Bragg angle, maxima at (1/ γ)on either side of 2𝜄𝐶.

• Intensity scales ~ quadratically with beam energy in

this range. Saturates at higher beam energy 𝛿 > 𝜕/𝜕𝑞

Freudenberger et al, Phys. Rev Lett 74, 248 (1995)

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Linewidth: geometric contributions

Significant

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Linewidth: multiple scattering

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Comparisons with experiments - 1

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Comparisons with experiments - 2

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Not included: detector efficiency, multiple scattering before crystal

ASTA: PXR

• T. Sen

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ASTA – PXR while channeling

Does not require rotations

• T. Sen

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ASTA: New goniometer

Available ports determine X-ray

energies Yield in photons/(el-sr)

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Spectral Brilliance Comparison

LEBRA (2013) ASTA

Beam energy Average beam current Normalized emittance Crystal X ray energy Photon yield/el Spectral brilliance 100 MeV 1-5 μA 15 μm Silicon 6.5 – 34 keV (220 ) 1.6x10-6 1.5x105 50 MeV ~ 200 nA 100 nm Diamond 9.8 keV (400 plane) 2.3x10-6 1.9x109

• Y. Hayakawa et al, J. Inst. (2013)

Absorption Phase Contrast

LEBRA, Nihon University, Japan

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X-Ray Source Comparison

Channeling PXR Inverse Compton Electron energy[MeV] Average current [μA]

• Norm. emittance [nm]

Spot size at target [nm] X-ray divergence [mrad] Photon energy [keV] Photon energy spread

• Av. Spectral brilliance

[photons/(s-(mm-mrad)2- 0.1% BW) 50 0.3 10 80 10 89, 142, 66 ~ 14% ~ 1012 50 0.3 10 80 10 3 – 18 ~ 1% ~1011 50 48 5000 20,000 10 50 ~1016

• Channeling and PXR: beam current is limited by crystal damage
• Channeling and PXR: assume field emitter cathodes
• T. Sen

X-arys and EUV at ASTA 38

Limitations

Beam current limits

• To avoid dead time losses, bunch repetition time > dead time
• f detector; so bunch repetition rate < 2.5 MHz (Amptek)
• Model developed to correct for pile-up; allows for more than

1 photon per bunch, i.e higher bunch charge (Wade Rush)

• Minimize heating & radiation damage to the crystal
• Backgrounds: from bremsstrahlung, requires shielding the

detector , measurement with crystal not in CR or PXR mode & subtraction

• Emittance: minimize growth from cathode to crystal
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Applications

• X-ray phase contrast imaging
• PXR / Transition radiation, as X-ray/EUV

generators with multi-layer structures

• Using EUV /X-rays for transverse/longitudinal

beam diagnostics.

• PXR generation in IOTA at multiple locations

with different energies

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Phase Contrast Imaging

Density profile Laplacian Absorption Phase Contrast

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Why PCI at ASTA?

• Simplest form of PCI method is

the propagation based method

• No optical aberrations
• Contrast & resolution are key
• Image contrast depends on
• Spatial coherence length

𝑀𝑑𝑝ℎ = λ𝑨1/s

• Source size (s) ~few nm is << than at light source synchrotrons
• Image resolution = detector resolution/M; M=(z1 + z2 )/z1
• Test state of the art deep depletion CCDs developed at the lab (DAMIC)

with high resolution and lower dosage (for medical imaging)

• 3D tomography is possible by changing z2
• Phase contrast imaging is an active research area
• ASTA can serve as a user facility for R&D in PCI.
• Model fpr a compact X-ray source with an X-band linac that could have

medical and industrial applications for PCI.

• T. Sen

X-arys and EUV at ASTA 42

Multi-layer mirrors

• Commercially available for X-ray

and EUV optics

• Materials depend on photon energy.
• Diffracted Transition Radiation (DTR) and PXR contribute. W/B4C

(400 layers, 1 nm each) on a Si substrate used for ~15 keV photons

• At photon energies > 𝛿𝜕𝑞 ~ 5keV (ASTA), PXR has higher intensity

and (apparently) with intensity > than a crystal of same thickness

• Complications: DTR, Bremsstrahlung etc are present.
• T. Sen

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EUV

• High power (~100W) required for lithography at 13.5

nm (92 eV)

• Low power uses: measurements & calibration of EUV
• ptical elements: mirrors, masks, photoresists,…
• T. Sen

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MLMs for EUV generation

• Recent results from Tomsk
• Beam energy = 5.7 MeV
• Average beam current= 100pA
• MLM made of 50 Mo/Si layers

thickness: 3.4 (Mo)/7.9 (Si) nm

• Si substrate, thickness=0.53mm
• Photon energy = (54 – 70) eV
• Expected photon rate=4.6x10-4 photons/(el-sr)
• Measured rate=2.4x10-4 photons/(el-sr)
• Estimated photon flux = 0.6x103 photons/s
• Scaling to ASTA energy (50 MeV) and current (~ 50 μA), expected

photon flux ~ 2x109 photons/s

• S. Uglov et al, IPAC 14
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X-arys and EUV at ASTA 45

Summary

• Models for channeling radiation & PXR show

reasonable agreement with earlier experiments

• ASTA: with 100 nm emittance, expect spectral

brilliance about 4 orders of magnitude higher than previous best, both for channeling and PXR.

• Field emitter cathode could improve this further.
• Well suited for testing & improving methods of

phase contrast imaging

• EUV generation possible with multi-layer mirrors

with photon flux higher by 6 orders of magnitude

• T. Sen

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Additional Slides

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X-arys and EUV at ASTA 47

Potential for inelastic thermal scattering

Expand imaginary potential in a Fourier series Extract the diffuse scattering intensity from the total scattered intensity: Assume small amplitude vibrations, & do thermal averaging to find Idiff . Find the imaginary potential from

PXR Contour Images

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X-arys and EUV at ASTA 49

Without broadening With broadening