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Introduction to Synchrotron Beamlines
Dr Richard Garrett Senior Advisor, Strategic Projects
R. Garrett 1st AOF Synchrotron School
Beamline Design Goals
(Good Luck!)
• Deliver the required X-ray beam to the experiment: – Energy and bandwidth – Spot size – Divergence/convergence
• Preserve source characteristics eg intensity, brightness, coherence
• Handle the heat load of the beam • Optimise signal / background • Be very stable and reproducible, in position, intensity
and energy • Be safe to operate • Be user friendly to operate • Achieve all the above within a reasonable budget !
R. Garrett 1st AOF Synchrotron School
Low energy electrons OR electron frame: Radiation in all directions Example: Radio waves from a transmitter.
High energy (relativistic) electrons – Laboratory frame: Radiation pattern swept into a narrow cone in the forward direction = High brightness!
E = electron beam energy
Generation of Synchrotron Radiation: Radiation from Accelerating Charge
R. Garrett 1st AOF Synchrotron School
Singapore Light Source 700 MeV
γ = 1400
.7 mrad .04º
Australian Synchrotron 3 GeV
γ = 6000
.2 mrad .01º
Spring-8 8 GeV
γ = 16000
.06 mrad .004º
2015 Cheiron School
εc = .665 E2B
K=0.934.λu[cm].B[T]
K>>1
K ~ 1
(on axis)
R. Garrett 1st AOF Synchrotron School
• Melting holes in things! and other damage.
• Thermal distortions of optics resulting in loss of intensity, focus etc
• An unstable X-ray beam due to long thermal equilibrium times
High Heat Load
Focused wiggler beam emerging into the air: NSLS X25 beamline.
• IMBL SC Wiggler: total power ~30 kW • in vacuum X-ray undulator: peak power density 15 kW/mrad2 at
k=1.8.
Consequences of poor design:
R. Garrett 1st AOF Synchrotron School
Synchrotron Optics
Professor David Attwood / UC Berkeley / AST 210/ EE213, Fall 2016, Chapter 10
Available x-ray optical techniques
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R. Garrett 1st AOF Synchrotron School
Mirrors for Synchrotron Beamlines
• Deflection
• Focusing
• Harmonic Rejection
• Power Reduction
R. Garrett 1st AOF Synchrotron School
X-ray Mirrors • At grazing angles, below the critical angle, reflectivity is
close to 1 • All common geometric figures can be produced with high
accuracy: – Flat mirrors – Cylindrical and spherical mirrors (produce spherical aberrations
except at 1:1 focus) – Elliptical mirrors: point to point focus – Parabolic mirrors: collimation and point focus from a parallel
beam • Due to the highly astigmatic focus (a spherical mirror
focuses almost entirely in the meridional direction) toroidal figures or separate horizontal and vertical focusing elements are often used.
R. Garrett 1st AOF Synchrotron School
Critical Angle/Reflectivity with Energy: Rhodium Coated Mirror Example
1 keV 10 keV 20 keV Harder X-rays need more
grazing angles and longer mirrors: 2 mm high beam needs: ≤ 10 cm mirror at 1 keV ≥ 80 cm mirror at 20 keV (grazing incidence long mirror does help with heat load )
Rh
Pt
Si
Mirror Reflectivity at 2.5 milli-radians Incidence
Such adjustable reflectivity/ high energy cutoff is very useful for harmonic rejection. Many beamlines have two or three different metal stripes coated side by side..
R. Garrett 1st AOF Synchrotron School
SPring-8
x (mm)
y (m
m)
σx = 316 µm σy = 4.9 µm
3rd Generation typical Undulator source size
2 mm
2 mm
Kirkpatrick-Baez Mirror Pair
Orthogonal mirrors cancel astigmatism Elliptical surfaces for point to point imaging
Glancing incidence coatings for broad band applications, multilayer coatings for fixed bandpass
Commonly used in synchrotron beamlines – separate vertical and horizontal focusing is a good match to the asymmetric source Courtesy of J. Underwood, LBNL
R. Garrett 1st AOF Synchrotron School
Bent Mirrors • The easiest figures to produce with high accuracy are
flats, cylinders and spheres • Large aspheric mirrors become very expensive: common
solution is a bent mirror: – Bent flat becomes a cylindrical mirror – Bent sagittal cylinder becomes a toroid
SESO mirror & single actuator bender
R. Garrett 1st AOF Synchrotron School
Mirror Cooling Water Channel
Copper fin in Ga filled slot
Thermal loads can easily destroy the mirror figure, degrading focal spots and losing intensity.
Side cooled mirror. Side cooling results in opposite thermal gradients at the center and the sides of the mirror. These gradients act against each other reducing the thermal deformation of the mirror.
R. Garrett 1st AOF Synchrotron School
Diffractive Optics:
Crystals, Gratings and Multilayers
R. Garrett 1st AOF Synchrotron School
λθ md =sin2
Crystals used at hard X-ray energies Bragg’s law:
d
θ
Monochromators: Crystals and Gratings Diffraction from periodic structures is used to select the desired energy from the “white” synchrotron radiation.
Double Crystal Monochromator
Monochromators all produce harmonics: Silicon Miller indices “Rule”:
• All Odd or • Divide by 4
So allowed reflections are: • <111>, <333> etc • <220>, <440> etc
Some Crystals used in Synchrotron Monochromators
Crystal 2d Energy Range
α-quartz (5052) 1.624 8.0 – 88 keV
Silicon (311) 3.274 4.0 – 44 keV
Silicon (220) 3.84 3.4 – 37 keV
Diamond (111) 4.118 3.2 – 35 keV
Silicon (111) 6.2712 2.1 – 23 keV
InSb (111) 7.4806 1.7 – 19 keV
Beryl (1010) 15.954 0.82 – 9 keV Source: ALS/CXRO X-ray Data Booklet & XOP
At soft X-ray energies crystal diffraction has difficulties: most large d-spacing crystals have significant imperfections, and absorption limits the penetration depth and therefore the resolution. Absorption edges can also result in structure on the monochromatic beam, eg Beryl contains Al with a k-edge at 1560 eV.
R. Garrett 1st AOF Synchrotron School
<111> <333>
Crystal Monochromators – Match to Source
AS Undulator
Bending Magnet 1/γ
• BM & wiggler: divergence >> Si natural width
• Normal DCM: 2nd crystal accepts same as first
• = worse energy resolution • Can slit beam but lose flux
• BM & wiggler – collimating mirrors recover resolution without sacrificing flux
• Undulator source – good match
R. Garrett 1st AOF Synchrotron School
Graphical Representation of Bragg’s Law
λθ md =sin2
R. Garrett 1st AOF Synchrotron School
Example: ChemMatCARS High Resolution Monochromator
Dumond diagram at 10 keV
R. Garrett 1st AOF Synchrotron School
Effect of Heat Load on Monochromator First Crystal
Heat “bump” on first crystal
No heating of first crystal
Thermal bump in water cooled Si crystal. Finite element calculation of undulator beam shows a 0.3 micron bump.
Thermal gradient = “Thermal Bump”
Two Solutions to Monochromator Heat Loads
Liquid Nitrogen Cooled Silicon Silicon coefficient of thermal expansion goes through zero near LN2 temperatures. A thermal gradient therefore does not produce a thermal “bump”.
“Inclined Geometry” Crystal Beam footprint spread out Thermal bump not in diffraction direction
APS LN2 cooled crystal Photo: D. Mills
Diffraction Gratings
α β
m = +1 m = +2
m = 0 m = -1
λαβ md =− )sin(sinThe grating equation. d = grating line spacing
Unlike crystal diffraction, all energies are diffracted all the time. An exit slit is needed to select a monochromatic beam. Zero order is not dispersed (grating acts like a mirror, ie α = β).
• Diffraction gratings are used from visible (and beyond) to soft X-ray energies. Gratings can function up to and above 2 keV, with decreasing efficiency
• Practical limit on line spacing is about 2000 lines/mm
• Most monochromators use first order diffraction
• Most gratings are “blazed”, ie the groove profile is figured to optimise for certain angle/wavelength ranges.
A schematic multilayer structure and a typical measured reflectivity spectrum. Layer A usually consists of a strongly absorbing material (metal). Layer B is a spacer made of a low-density material.
Multilayer Optics Multilayers can be deposited on mirrors or gratings to increase the reflectivity, although only over a limited energy range. Double multilayer monochromator has higher bandpass & intensity than DCM.
R. Garrett 1st AOF Synchrotron School
Graded Multilayers
• Multilayers can be graded (layer period varied) laterally or with depth
• Lateral grading is needed for focusing multilayers
• Depth grading can be used to produce a “Super Mirror”
• In example shown, a normal grazing mirror cuts under 10 keV at 0.5 degree incidence. (Erko etal)
R. Garrett 1st AOF Synchrotron School
Micro-focus Optics
R. Garrett 1st AOF Synchrotron School
Summary of Micro-focus Optics
Focus Spot Energy Range Other Characteristics
Zone Plate 0.1 μm (hard) .06 μm (soft)
< 25 keV Good resolution Focus moves with energy
K-B Mirror ~10nm (Osaka) .3 μm (ESRF) Typical ~1 μm
< 25keV Resolution improving fast! Focus fixed H & V decoupled
Refractive Lens ~ 1 μm < 100 keV High X-ray energy Focus moves with energy
Capillary .05 μm < 20 keV Very short working distance
R. Garrett 1st AOF Synchrotron School
• resolution is limited by smallest feature size b:
∆x = 1.22 b
• highly chromatic: f ~ 1/λ
• mostly have several diffraction orders
∆x
b
Zone Plates: Basic properties
Scanning electron micrograph of 40 nm outermost zones
X-ray Zone Plates
R. Garrett 1st AOF Synchrotron School
With 0.24 x 0.18 mm2 (v x h) acceptance Spot size = 0.34 x 0.27 µ m2 FWHM
KB mirrorset-up with Xray CCD based focus spot measurement
Kirkpatrick Baez Optics - O. Hignette et al. (ESRF)
Professor David Attwood / UC Berkeley / AST 210/ EE213, Fall 2016, Chapter 10
X-ray nanoprobe based on crossed ellipses
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Courtesy of S. Matsuyama and K. Yamauchi (Osaka university). S. Matsuyama et al., Rev. Sci. Instrum.77, 103102 (2006).
Nanofocus fluorescence beamline @ Spring-8. Elemental distribution maps18 of Cu and Zn, are seen within the nucleus of a single NIH/3T3 cell. Maps of P, S, Cl, Ca and Fe also reported
Compound Refractive Lenses
Snigirev etal
• Refractive index is <1 so concave lens focuses • Refraction is very small so many lenses normally stacked • Low absorption materials needed, eg Be, Al
SEM image of an array of parabolic refractive X-ray lenses made of silicon. The shaded areas (i) and (ii) show an individual and a compound lens, respectively. (ESRF)
Professor David Attwood / UC Berkeley / AST 210/ EE213, Fall 2016, Chapter 10
Multilayer Laue Lenses (MLL) for focusing hard x-rays
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Courtesy of H.Yan, National Synchrotron Light Source (NSLS), BNL.
Optimum performance is obtained with curved multilayer zones of graded d-spacing that satisfy the Bragg condition everywhere.
R. Garrett 1st AOF Synchrotron School
Complete Beamlines
A Simple X-ray Beamline: the ANBF (1992-2012)
*
Bending Magnet Source
Be Window
Beamline Slits
Channel Cut Si<111> Mono
Safety Shutter
Hutch Wall
Be Window
R. Garrett 1st AOF Synchrotron School
AS Xray Absorption Spectroscopy Beamline
R. Garrett 1st AOF Synchrotron School
DCM K-B mirror
AS SAXS/WAXS Beamline
Undulator Beamlines
Nano-focus fluorescence beamline @ Spring-8
R. Garrett 1st AOF Synchrotron School
Example Soft X-ray Beamline (NSRRC Taiwan)
Professor David Attwood / UC Berkeley / AST 210/ EE213, Fall 2016, Chapter 10
Bio-nanotomography for 3D imaging of cells
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Courtesy of C. Larabell (UCSF & LBNL) and M. LeGros (LBNL)
λ = 2.4 nm
Soft X-Ray Nanotomography of a Yeast Cell
Nanotomography of Cryogenic Fixed Cells
λ = 2.4 nm (517 eV) Δr = 35 nm N = 320 NA = 0.034 D = 45 µm f = 650 µm σ = 0.64 Resolution = 60 nm 3 min total time
R. Garrett 1st AOF Synchrotron School
New 4th Generation Light Sources
PETRA III @ DESY MAX IV in Lund NSLS II @ BNL
εh = 1 nm rad @ 6 GeV εh = 0.2-0.3 nm rad @ 3.7 GeV εh = 0.55 nm rad @ 3 GeV
Spring-8 in Hyogo, Japan APS @ ANL
εh = 0.07 nm rad @ 6 GeV
ESRF in Grenoble
εh = 0.1-0.15 nm rad @ 6 GeV εh = 0.11 nm rad @ 6 GeV
Upgrades to 4th Gen
R. Garrett 1st AOF Synchrotron School
SPring-8 SPring-8-II
x (mm)
y (m
m)
σx = 27.3 µm σy = 6.4 µm
σx = 316 µm σy = 4.9 µm
Comparison of undulator source size
2 mm
x (mm)
y (m
m)
2 mm 2 mm
R. Garrett 1st AOF Synchrotron School
http://xdb.lbl.gov/ X-ray data booklet “the orange book”
http://www.csrri.iit.edu/periodic-table.html Periodic table of X-ray absorption edges and emission energies
http://www.lightsources.org/regions list of light sources
https://www1.aps.anl.gov/Science/Scientific-Software/XOP assembly of codes to calculate BM, wiggler & undulator sources, mirror & filter transmissions & more
https://forge.epn-campus.eu/projects/shadow3 Shadow ray tracing package
etc
Online Resources:
Thank you
ansto.gov.au