Introduction to Synchrotron Radiation

Transcription

1 Introduction to Synchrotron Radiation Frederico Alves Lima Centro Nacional de Pesquisa em Energia e Materiais - CNPEM Laboratório Nacional de Luz Síncrotron - LNLS International School on Laser-Beam Interactions UFRN - Natal, Brazil September 2016

2 Outline Tools for structural analysis History of X-rays Synchrotron Radiation LNLS & SIRIUS: Synchrotron Radiation in Brazil

3 Why do we need to study structure Structure - X-ray crystallography - electron microscopy - atomic force microscopy - electron diffraction - X-ray absorption spectroscopy - NMR Dynamics - Laser spectroscopy - NMR - Time-resolved diffraction & XAS - Time-resolved PES Graphene Manganite: atomic motion coupled by charge and orbital order Fullerene Photosystem II Nanotube Rotating hydrated Mb molecule Layer-selective spin dynamics in magnetic multilayers

4 What are the length scales involved?

5 The Electromagnetic Spectrum Electromagnetic wave Light! Orthogonal and alternating electric and magnetic fields that propagate into space. Set of equations describing how electric and magnetic fields are generated and altered by each other and by charges and currents. James Clerk Maxwell Maxwell s equation of electromagnetism

6 The Electromagnetic Spectrum 700 nm 400 nm X-ray proper tool to investigate atoms.

7 History of X-rays In the evening of Nov. 8th 1895 Wilhem Röntgen first detected x-rays He found that when running a high-voltage discharge tube enclosed in thick black cardboard which excluded all visible light, in his darkened room, a paper plate covered on one side with barium platinocyanide would fluoresce, even when it was as far as 2 m from the discharge tube. X-rays! He soon discovered that these x-rays also stained photographic plates and latter demonstrated that objects of different thicknesses showed different degrees of transparency. First x-ray photograph of a human hand with a ring probably from his wife!

8 Synchrotron Radiation We need an extremely bright source of x-rays Synchrotron source area S divergence flux F Ω brightness / F S Synchrotrons are very bright because the source size and divergence are very small. But why is that?

9 Synchrotron Radiation Accelerated electric charge electromagnetic radiation In the non-relativistic case, the dominant emission from an electric charge is dipolar. Maxwell s equation! 0! 0 The emitted power and spectrum are proportional do the acceleration, was given by the Larmor formula. Acceleration is usually a function of t, resulting in a certain distribution of the emitted energy. antenna

10 Synchrotron Radiation Decelerated electric charge Bremsstrahlung radiation (Non-relativistic) charges colliding with a target also emit radiation with a dominant dipolar contribution. X-ray tube X-ray spectrum of a Silver target (anode) as a function of the voltage. Note the different emission lines and also the Bremsstrahlung radiation.

11 Synchrotron Radiation Relativistic limit + acceleration synchrotron radiation Relativistic electrons can be accelerated by a magnetic field through the Lorentz force ~F = q( ~ E + ~v ~ B) Emitted radiation cone has an angular opening depending on the Lorentz factor = ", that is: mc 2 1 Synchrotron source

12 Synchrotron Radiation: bending magnets Magnetic field used to change the propagation direction of electric charges in movement The critical energy of radiation emitted by bending magnets depends on the energy of the accelerated electrons.

13 Synchrotron Radiation: insertion devices Alternating magnetic poles make electric charges 'wiggle' Wiggler Undulator

14 Insertion devices in reality

15 How to produce Synchrotron radiation?

16 Synchrotron Radiation Main components: - LINAC: linear accelerator - Booster - Storage ring - Beamlines Where are the synchrotron sources?

17 Synchrotron Radiation: Optics

18 Synchrotron Radiation: stored electrons Stored electrons are in dynamic equilibrium inside the lattice Concrete wall shielding Front-end Insertion device Bending magnet RF cavity restores the energy lost each turn. It also generates a potential well in the storage ring which is responsible for packing the electrons in bunches. Resonant RF cavity Synchrotron radiation is intrinsically pulsed Experiments exploiting temporal resolution!

19 X-ray Free-Electron Lasers Resonant condition: The slippage between the electromagnetic wave and a given electron, while the electron advances by one undulator period must be equal to the field wavelength. SASE - Self Amplified Spontaneous Emission Micro-bunching rad = (1 + K2 eff /2) K eff =0.934 rad B eff Long undulators are needed as the saturation of the micro-bunching effect is a function of the length.

20 X-ray Free-Electron Lasers The result is a tremendous increase in the peak brilliance! X-ray FEL s generate laser-like radiation: coherent x-rays and with ultrafast temporal duration (femtosecond pulses!) Ultrafast dynamics Single-molecule diffraction Coherent imaging/scattering Investigation of Small quantum systems Non-linear X-ray Matter under extreme conditions et cetera Completely new science could be done at XFELs!

21 Interaction of X-rays with Matter How does electromagnetic radiation interact with matter? - Scatter - Diffraction - Absorption - We make use of these phenomena to design experiments that help us to elucidate the properties of matter. - Small/Wide Angle X-ray Scattering - X-ray Diffraction - X-ray Absorption Spectroscopy

22 Structural characterization using x-rays Scattering sample Int q

23 Structural characterization using x-rays Diffraction istal histidine ligand istal histidine proximal histidine ligand proximal histidine

24 Structural characterization using x-rays Absorption X-RAYS An x-ray photon is absorbed by an atom ejected an electron, which then propagates in the material using the excess energy. I / I0 1 Z Norm. µ(e) [a.u.] X-ray energy [kev]

25 Synchrotron Radiation Around the World Brazil has one such light source operating since 1997!

26 CNPEM - LNLS & SIRIUS LNLS: research and development using synchrotron radiation LNBio: research on biosciences LNNano: research on nano(materials) CTBE: research on ethanol production SIRIUS%

27 Synchrotron Radiation LNLS

28 Synchrotron Radiation in Brazil Laboratório Nacional de Luz Síncrotron: LNLS - One out of the 4 labs (LNLS, LNNano, LNBio & CTBE) of the CNPEM - 18 beamlines operating

29 LNLS User community Other States São Paulo Other countries In proposals 180 users In proposals 1200 users 18 beamlines 7 beamlines

30

31 CNPEM: areas of actuation - Synchrotron Light Source operation and development - Material s science - Molecular biology - NMR spectroscopy - Mass spectrometry - Electron microscopy & Scanning probe microscopy - Mechanical microfabrication - Chemical synthesis - Engineering (scientific instrumentation) - Bioethanol research - etc

32 Summary CNPEM is a multi-disciplinary research center with cutting edge equipment and staff Structure & dynamics are important to determine how materials function X-rays are suitable to study atomic scale Synchrotron light indispensable scientific & technologic tool To produce SR we need accelerated relativistic charges (e-) The SR has very special characteristics - Hight brightness - Very collimamated - (Almost) continuum spectrum

33 Thank you