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

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

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 electrons @ 5 GeV EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 3

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. EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 4

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 5

(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) 1900 1920 1940 1960 1980 2000 Years EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 6

A tool for a wide range of applications Environment science Materials Science Biology Physics Medicine Chemistry EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 7

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 8

A synchrotron radiation beamline Storage ring Optics cabin Experiments cabin Control room EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 9

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 10

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 11

Permanent magnet undulators Standard undulators In-vacuum Cryogenic Arrays of rare earth magnets (NdFeB, SmCo) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 12

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 13

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): 10-4 (few eV @ 20keV) Photon flux (dE/E = 10-4): 1013 - 1014 ph/sec Focused beam size: few mm (routinely achieved) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 14

SR experimental stations Integrate: Sample conditioning/environment equipment Mechanical setup Detection system EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 15

X-ray Diffractometers EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 16

Example: catalytic reactor for surface chemistry Flow reactor for catalysis studies EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 17

Example: macromolecular X-ray diffraction station High precision spindle Cryostream X-ray beam Detector Sample Automatic sample changer EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 18

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 19

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) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 20

“Families” of X-ray SR experiments/detectors Simplified classification by application / type of interaction: Elastic scattering Inelastic scattering Absorption / fluorescence spectroscopy Imaging EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 21

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) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 22

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 23

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) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 24

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 (0.5 - 40 mm) Indirect detection scheme: Scintillating screen + Lens coupling Visible light camera (CCD based) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 25

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 EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 26

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) EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 27

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. EIROforum School on Instrumentation – Geneva – May 2009 P. Fajardo 28