1. Introduction to Synchrotron Radiation Instrumentation
Pablo Fajardo
Instrumentation Services and Development Division
ESRF, Grenoble
EIROforum School on  Instrumentation (ESI 2009)

2. Outline 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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3. Synchrotron Radiation (SR)
Synchrotron radiation is produced by relativistic charged particles
accelerated by magnetic fields. It is observed by particle accelerators.
The emission is concentrated in the forward direction
natural SR divergence: 1/g ~ 100mrad for 5 GeV
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4. Synchrotron radiation
First use of synchrotron radiation
1947
First observation of synchrotron radiation at General Electric (USA).
Particle
physics
Synchrotron radiation
First
particle
accelerators
Particles
with more and more
energy
bigger and bigger machines
observation
of synchrotron
radiation
Construction of the first
“dedicated”
machines
1930
1947
1980
Initially considered a nuisance by particle physicists,
today synchrotron radiation is recognised as an exceptional means of exploring matter.
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5. Brilliance
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 detector or
high energy, spatial, angular or time resolution
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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6. (photons/s/mm2/mrad2/0.1%BW)
SR light properties
Free
electron
lasers
Brilliance
(photons/s/mm2/mrad2/0.1%BW)
Very high brilliance
Wide spectrum
But also :
Polarisation (selectable)
Coherence (small source size)
Pulsed emission (e- bunches)
Years
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7. A tool for a wide range of applications
Environment science
Materials Science
Biology
Physics
Medicine
Chemistry
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8. Synchrotron radiation facilities
Current generation: low emittance storage rings
Circular 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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9. A synchrotron radiation beamline
Storage ring
Optics cabin
Experiments cabin
Control room
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10. Insertion 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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11. Storage 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
magnet arrays
electron beam
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12. Permanent magnet undulators
Standard undulators
In-vacuum
Cryogenic
Arrays of rare earth magnets (NdFeB, SmCo)
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13. Beam delivery/conditioning
X-ray optics
Select photon energy (monochromators)
Steer and focus the photon beam
Manage the power (heat load)
Beam control
Precision mechanics (mm, mrad) 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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14. Some 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 (dE/E): (few 20keV)
Photon flux (dE/E = 10-4): ph/sec
Focused beam size: few mm (routinely achieved)
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15. SR experimental stations
Integrate:
Sample conditioning/environment equipment
Mechanical setup
Detection system
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16. X-ray Diffractometers
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17. Example: catalytic reactor for surface chemistry
Flow reactor for catalysis studies
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18. Example: macromolecular X-ray diffraction station
High precision spindle
Cryostream
X-ray beam
Detector
Sample
Automatic sample changer
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19. Example of sample environment: high pressure cells
45 mm
Diamond anvil cell (DAC)
Very small sample volume (~100mm)
Pressure control up to ~1 Mbar
Reference material (ruby) for monitoring
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20. Extreme P-T conditions in a pressure cell
Laser path
Diamond Anvil Cell
focusing optics
Beam splitting system
Detector
SR X-ray beam
Laser
beamstop
Pressure: up to 1 Mbar (diamond anvil cell)
Temperature: up to 3000 °C (laser heating)
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21. “Families” of X-ray SR experiments/detectors
Simplified classification by application / type of interaction:
Elastic scattering
Inelastic scattering
Absorption / fluorescence spectroscopy
Imaging
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22. 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)
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23. Inelastic 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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24. Absorption / fluorescence spectroscopy
Absorption spectroscopy:
- Sample absorption (as a function of energy)
- Polarization dependence (dichroism)
- Measure either:
Transmitted intensity (I1/I0) or
Fluorescence yield
- Detectors:
Intensity: ion chambers, photodiodes
Fluorescence: semiconductor 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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25. Imaging detectors The detector sees an image of the sample
(absorption or phase contrast)
Very high flux on the detector (~1014 ph/sec)
Small pixels ( mm)
Indirect detection scheme:
Scintillating screen +
Lens coupling
Visible light camera
(CCD based)
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26. 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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27. Efficiency 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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28. Summary
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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