introduction to synchrotron beamlinesarchive.synchrotron.org.au/images/aof2017/6-beamline... ·...

$: Introduction to Synchrotron Beamlinesarchive.synchrotron.org.au/images/AOF2017/6-Beamline... · 2017. 6. 1. · Unlike crystal diffraction, all energies are diffracted all the time$
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 !


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


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)


• 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:


Synchrotron Optics

Professor David Attwood / UC Berkeley / AST 210/ EE213, Fall 2016, Chapter 10

Available x-ray optical techniques

8


Mirrors for Synchrotron Beamlines

• Deflection

• Focusing

• Harmonic Rejection

• Power Reduction


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.


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..


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


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


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.


Diffractive Optics:

Crystals, Gratings and Multilayers


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.


<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


Graphical Representation of Bragg’s Law

λθ md =sin2


Example: ChemMatCARS High Resolution Monochromator

Dumond diagram at 10 keV


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.


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)


Micro-focus Optics


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


• 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


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)


X-ray nanoprobe based on crossed ellipses

34

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)


Multilayer Laue Lenses (MLL) for focusing hard x-rays

36

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.


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


AS Xray Absorption Spectroscopy Beamline


DCM K-B mirror

AS SAXS/WAXS Beamline

Undulator Beamlines

Nano-focus fluorescence beamline @ Spring-8


Example Soft X-ray Beamline (NSRRC Taiwan)


Bio-nanotomography for 3D imaging of cells

42

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


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


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


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:

http://xdb.lbl.gov/

http://www.csrri.iit.edu/periodic-table.html

http://xdb.lbl.gov/

http://www.lightsources.org/regions

https://www1.aps.anl.gov/Science/Scientific-Software/XOP

https://forge.epn-campus.eu/projects/shadow3

Thank you

ansto.gov.au

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