Introduction to Synchrotron Radiation Instrumentation

Introduction toSynchrotron Radiation Instrumentation

Pablo FajardoInstrumentation Services and Development DivisionESRF, Grenoble

EIROforum School on Instrumentation (ESI 2009)

EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 2

OutlineOutline

Characteristics of synchrotron radiation (SR)

SR facilities and beamlines• Radiation sources: undulators• Beam delivery and conditioning• Examples of experimental stations

Types of experiments / detection schemes

A few final comments


Synchrotron Radiation (SR)Synchrotron Radiation (SR)

electron orbit

SR emission~1/g = mc2/E

acceleration

Synchrotron radiation is produced by relativistic charged particlesaccelerated by magnetic fields. It is observed by particle accelerators.

The emission is concentrated in the forward directionnatural SR divergence: 1/g ~ 100rad for electrons @ 5 GeV


First use of synchrotron radiationFirst use of synchrotron radiation

Initially considered a nuisance by particle physicists,today synchrotron radiation is recognised as an exceptional means of exploring matter.

1947

First observation of synchrotron radiation at General Electric (USA).

Particlephysics

Synchrotron radiation

Firstparticle

accelerators

Particleswith more and more

energy

bigger and bigger

machines

Firstobservationof synchrotronradiation

Construction of the first“dedicated”machines

1930

1947

1980


BrillianceBrilliance

The singular characteristic of SR beams is their high brilliance.

High brilliance beams = high flux of “useful photons”

high photon fluxes at the sample and detectoror

high energy, spatial, angular or time resolutionor

any compromise between the previous two

brilliance of SR beams depends on the accelerator emittance.

(low emittance = small size and divergence of the particle beam)

SR Brilliance = photon flux / source area / solid angle / spectral interval


SR light propertiesSR light properties

• Very high brilliance

• Wide spectrum

But also :

• Polarisation (selectable)

• Coherence (small source size)

• Pulsed emission (e- bunches)

Years1900 1920 1940 1960 1980 2000

Freeelectron

lasersBrilliance

(photons/s/mm2/mrad2/0.1%BW)

1900 1920 1940 1960 1980 2000

ESRF (1994)

2ème generation

1ère génération

Tubes àrayons X

Années

ESRF (futur)

Limite de diffraction

ESRF (2000)3èmegeneration

Lasers àélectrons libres

Rayonnementsynchrotron

1020

1018

1016

1014

1012

1010

108

1021

1022

1023

1019

1017

1015

1013

1011

109

107

106

Brillance(photons/s/mm2/mrad2/0.1%B.F.)

X-ray tubes

1st generation

2nd generation

3rd generation

ESRF 2005

ESRF 2000

ESRF 1994


A tool for a wide range of applicationsA tool for a wide range of applications

Materials Science

Biology

Environmentscience

Physics

Medicine

Chemistry


Synchrotron radiation facilitiesSynchrotron radiation facilities

Current generation: low emittance storage ringsCircular accelerators operating typically with few GeV electrons.

Further reduction of emittance is difficult in storage rings but possible with LINACs (low duty cycle: pulsed sources)

enormous peak brilliance free-electron lasers


A synchrotron radiation beamlineA synchrotron radiation beamline

Undulator

Storage Ring

e-

X-ray optics, slits, diagnostics

Experimental station, sample, detector

Storage ring

Optics cabin

Experiments cabin

Control room


Insertion devices: undulators and wigglersInsertion devices: undulators and wigglers

Electrons (or positrons) emit SR as they wiggle across N magnetic field periods (transverse oscillations).

Does each electron interfere with its own field?

NO WIGGLER emission ~N

YES UNDULATOR emission ~N2


magnet arrays

electron beam

Storage rings vs. free electron lasersStorage rings vs. free electron lasers

X-ray undulator emission is a spontaneous process

Two types:

Storage Rings - non-amplified emission

Electrons emit independently

High duty cycle (low energy losses)

Free-electron Lasers - self-amplified emission (SASE)

Electrons emit coherently

Require low electron emittance (LINAC) + long undulators

Pulsed sources (very short pulses), low duty cycle


Permanent magnet undulatorsPermanent magnet undulators

Standard undulators

In-vacuum

Cryogenic

Arrays of rare earth magnets (NdFeB, SmCo)


Beam delivery/conditioningBeam delivery/conditioning

X-ray optics• Select photon energy (monochromators)• Steer and focus the photon beam• Manage the power (heat load)

Beam control• Precision mechanics (m, rad) nearly everywhere • Remote control is mandatory• Large number of actuators (motors, piezoelectric devices)

Diagnostics• Beam viewers (off-line)• On-line position and intensity monitors


Some numbers / orders of magnitudeSome numbers / orders of magnitude

White beams:• Total emitted power (white beam): ~1 kW• Beam size (at 20 m): few mm

Monochromatic X-ray beams:• Typical energy bandwidth (E/E): 10-4 (few eV @ 20keV)• Photon flux (E/E = 10-4): 1013 - 1014 ph/sec• Focused beam size: few m (routinely achieved)


SR experimental stationsSR experimental stations

Integrate:- Sample conditioning/environment equipment- Mechanical setup- Detection system

Detector

SR beam

Sample

Sample environment

Temperature (oven, cryostat)Pressure (vacuum – Mbar)Magnetic fieldsMechanical stressChemical reactions...

Mechanical setup

AlignmentSample orientationScanning (translations, rotations)...

Diagnostics

Filters


X-ray DiffractometersX-ray Diffractometers


Example: catalytic reactor for surface chemistry Example: catalytic reactor for surface chemistry

Flow reactor for catalysis studies


Example: macromolecular X-ray diffraction stationExample: macromolecular X-ray diffraction station

Sample

X-ray beamDetector

High precision spindle Cryostream

Automatic sample changer


Example of sample environment: high pressure cellsExample of sample environment: high pressure cells

45 mm45 mm

Diamond anvil cell (DAC)

Very small sample volume (~100m)

Pressure control up to ~1 Mbar

Reference material (ruby) for monitoring


Extreme P-T conditions in a pressure cellExtreme P-T conditions in a pressure cell

Beam splitting system

Diamond Anvil CellLaser path

Laser

beamstop

focusing optics

SR X-ray beamDetector

Pressure: up to 1 Mbar (diamond anvil cell)Temperature: up to 3000 °C (laser heating)


““Families” of X-ray SR experiments/detectorsFamilies” of X-ray SR experiments/detectors

Simplified classification by application / type of interaction:

• Elastic scattering

• Inelastic scattering

• Absorption / fluorescence spectroscopy

• Imaging

Transmission

SampleIncidentbeam

Fluorescence

MicroscopyImaging

Absorption spectroscopy

electrons

Photoemission

Elastic scatteringdiffraction

Inelasticscattering

change in energy


Elastic scattering (diffraction, SAXS, …)Elastic scattering (diffraction, SAXS, …)

• Scattered photons conserve the same energy than incident

• Solid angle collection (scanning, 1D or 2D)

• Spatial resolution depend on detector-sample distance

• Large dynamic range requirements (many orders of magnitude)

• Type of detectors:- PMTs, APDs- Solid state (strip, hybrid pixels)- Image plates, flat panels- CCDs (mostly indirect detection)

Detector

Incident SR beam

Sample

scattered photons


Inelastic scatteringInelastic scattering

• Require the measurement of the recoil energy transferred to the sample by the X-rays.

• Very high energy resolution required: 1meV – 1eV (for hard X-rays)

• Use of wavelength dispersive detection setups: High resolution crystal analyzers + photon detector

• Needs highly monochromatic radiation

• Very low photon fluxes (counting)

• Position sensitivity detection helps to improve energy resolution


Absorption / fluorescence spectroscopyAbsorption / fluorescence spectroscopy

Absorption spectroscopy:- Sample absorption (as a function of energy)- Polarization dependence (dichroism)- Measure either:

Transmitted intensity (I1/I0) orFluorescence yield

- Detectors: Intensity: ion chambers, photodiodes Fluorescence: semiconductor detectors

Fluorescence Detector

(energy dispersive)

Energy tunable incident X-ray beam

Sample

transmitted beam

I1I0

Intensity detectors

Fluorescence analysis:• Measurement of fluorescence lines

chemical analysis, mapping, ultra-dilute samples• Detection:

Semiconductor detectors, (Si, Ge, SDDs)Wavelength dispersive setups (crystal analyzers)


Imaging detectorsImaging detectors

• The detector sees an image of the sample (absorption or phase contrast)

• Very high flux on the detector (~1014 ph/sec)

• Small pixels (0.5 - 40 m)

• Indirect detection scheme:

Detector

Incident SR beam

Sample

transmitted beam

Scintillating screen+

Lens coupling+

Visible light camera(CCD based)


What about soft X-rays?What about soft X-rays?

The previous cases/examples apply mostly to hard X-rays (> 2 keV)

Soft X-ray detection is in general considered “less relevant” Scattering cross-sections are low with soft X-rays, absorption

dominates No Bragg diffraction, main fluorescence lines are not excited X-ray imaging requires sufficient beam transmission (~ 30%)

However some experiments need soft X-ray detectors: Certain resonant scattering techniques need X-rays tuned to L or M

edges X-ray microscopy benefits from soft X-rays (thin samples, full-field

optics) It is easier to produce coherent beams at long wavelengths

Many soft X-ray beamlines are devoted to electron spectroscopy


Efficiency in SR experimentsEfficiency in SR experiments

Data collection efficiency is crucial to shorten the experiments:

High cost of SR facilities (true for any large facility)

Efficiency opens the door to shorter time scales (study of dynamic processes). Often the number of photons does not limit.

Radiation damage limits the duration of the experiments Samples may receive dose rates of ~Grad/sec with focused beams Detectors suffer also high irradiation doses

Ways of increasing efficiency:• Detection efficiency (DQE)• Area/solid angle (2D instead of point or 1D detectors)• Time (reduced deadtime, high duty cycles)


SummarySummary

Synchrotron radiation is a very useful tool for a variety of scientific disciplines.

Large SR facilities are optimised for production of X-rays.

High brilliance of SR sources is the key figure of merit.

X-ray FELs are a new type of “pulsed” photon sources complementary to storage rings.

Experiments are most often built around the sample. Experimental setups depend very much on the characteristics of the sample.

SR detectors have to deal often with high photon fluxes and push the spatial, energy and time resolution. Detection efficiency is extremely important as it allows reaching shorter time domains.

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Introduction to Synchrotron Radiation Instrumentation