Introduction to Synchrotron Radiation Instrumentation

1. Introduction toSynchrotron 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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo2

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 electrons @ 5 GeV EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo3

4. 1930 First particle accelerators First observation of synchrotron radiation 1947 Particles with more and more energy bigger and bigger machines 1980 Construction of the first “dedicated” machines Particle physics Synchrotron radiation First use of synchrotron radiation 1947 First observation of synchrotron radiation at General Electric (USA). 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 2009P. Fajardo4

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 or any compromise between the previous two • brilliance of SR beamsdepends 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 2009P. Fajardo5

6. 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 2009P. Fajardo6

7. Materials Science Biology Environmentscience Physics Medicine Chemistry A tool for a wide range of applications EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo7

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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo8

9. Storage ring Optics cabin Experiments cabin Control room A synchrotron radiation beamline EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo9

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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo10

11. magnet arrays electron beam 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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo11

12. Permanent magnet undulators Standard undulators In-vacuum Cryogenic Arrays of rare earth magnets (NdFeB, SmCo) EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo12

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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo13

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): 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 2009P. Fajardo14

15. SR experimental stations • Integrate: • Sample conditioning/environment equipment • Mechanical setup • Detection system EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo15

16. X-ray Diffractometers EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo16

17. Example: catalytic reactor for surface chemistry Flow reactor for catalysis studies EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo17

18. High precision spindle Cryostream Sample Automatic sample changer Example: macromolecular X-ray diffraction station X-ray beam Detector EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo18

19. Diamond anvil cell (DAC) 45 mm Example of sample environment: high pressure cells • Very small sample volume (~100mm) • Pressure control up to ~1 Mbar • Reference material (ruby) for monitoring EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo19

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) EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo20

21. “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 2009P. Fajardo21

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) EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo22

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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo23

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) EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo24

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 (0.5 - 40 mm) • Indirect detection scheme: • Scintillating screen • + • Lens coupling • + • Visible light camera • (CCD based) EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo25

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 EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo26

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) EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo27

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. EIROforum School on Instrumentation– Geneva – May 2009P. Fajardo28