introduction to synchrotron radiation instrumentation
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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
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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
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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
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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
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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
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A tool for a wide range of applicationsA tool for a wide range of applications
Materials Science
Biology
Environmentscience
Physics
Medicine
Chemistry
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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
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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
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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
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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
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Permanent magnet undulatorsPermanent magnet undulators
Standard undulators
In-vacuum
Cryogenic
Arrays of rare earth magnets (NdFeB, SmCo)
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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
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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)
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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
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X-ray DiffractometersX-ray Diffractometers
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Example: catalytic reactor for surface chemistry Example: catalytic reactor for surface chemistry
Flow reactor for catalysis studies
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Example: macromolecular X-ray diffraction stationExample: macromolecular X-ray diffraction station
Sample
X-ray beamDetector
High precision spindle Cryostream
Automatic sample changer
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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
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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)
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““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
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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
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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
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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)
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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)
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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
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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)
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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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