Photon Science
at
SLAC National Accelerator Laboratory
Joachim Stöhr
LCLS Director
SLAC was founded in 1962:
Over the first 40 years SLAC scientists helped to
establish the “Standard Model of Particle Physics”
SLAC Professor
Richard
Taylor
Nobel Prize 1990
LINAC completed in 1966
280 Overpass
SPEAR completed in 1972
x-ray experiments began in 1974
SLAC Professors Burton Richter (Nobel 1976)
and Martin Perl (Nobel 1995)
Stanford Board of Trustees
Page 4
1999: Particle Physics Gets a Surprise!
Studied with particle
accelerators 1960-2000
LHC?
Nobel Prize in Physics
2011
SLAC particle physics research shifted to address this challenge
CAS Dry Run: October 19, 2011 (J. Stöhr)
5
Over last six years, SLAC has shifted
its focus away from particle physics
$450
Total
$400
$350
$ Millions
$300
Photon
Science
$250
$200
$150
$100
Particle
& Astro
$50
$0
FY2000
FY2001
FY2002
FY2003
FY2004
FY2005
FY2006
FY2007
FY2008
FY2009
FY2010
FY2011
FY2012
SLAC National Accelerator Laboratory:
A proud history and an exciting future
From particles to photons
Change in Mission reflected in
SLAC Organization Chart
SLAC Director
Operations
Accelerators
LCLS
SSRL
Photon
Science
“Photon Science”
consists of
• x-ray user facilities
• x-ray research
Particle & Particle
Astrophysics
SIMES
PULSE
SUNCAT
….
SLAC operates two world class x-ray user facilities
LCLS
SSRL storage ring
electron beam
x-ray beam
SLAC played an important role in the last two
revolutions in “light”
• 1879 - Invention of the light bulb
• 1895 - Discovery of X-Rays
• 1960 - Invention of the LASER
• 1974 - Synchrotron radiation x-rays: SSRL
• 2009 - The first x-ray laser: LCLS
What is SSRL known for?
• Development of X-Ray Absorption Techniques: EXAFS, SEXAFS, NEXAFS
• Development of MAD (multiple wavelength anomalous dispersion) phasing
• Pioneering Soft X-Ray Science (200 – 3000 eV) (Grasshopper, Jumbo)
• Development of Synchrotron-Based Photoemission Techniques
• especially core level photoemission, photoelectron diffraction, and ARPES
• Development of grazing incidence surface and interface scattering
• First Application of Wigglers and Undulators
• Pioneered Coronary Angiography (medical imaging)
• Pioneered Magnetic Microscopy with X-Rays
• Pioneered X-Ray Studies in Molecular Environmental Science
X-Rays from Electron Storage Ring
X-Ray pulse length determined by electron bunch length
Bunch width ~ 100 ps
Bunch spacing 2 ns
beam line
x-ray pulses
~ 100 ps width
Can make shorter pulses (~ 1ps) at great loss of intensity
Introduction to LCLS
What is a
x-ray free electron laser, anyway?
Optical versus X-Ray Free Electron Laser
Optical laser
• bound electrons in atoms
- transitions between discrete states
• amplification through stimulated
emission
• fixed photon energy around 1 eV
• compact size
X-ray free electron laser
• free relativistic electrons in bunch
- radiation in periodic H-field
• amplification through
 electron ordering in its own
radiation (SASE)
 electron ordering in imposed
radiation (seeding)
• tunable photon energy up to 20 keV
• very large size
SASE versus self seeded x-ray beam
Intense x-ray source
with spiky spectrum
Monochromator filter
creates seed with
controlled spectrum
seeded
SASE
FEL amplifier
(exponential
intensity gain)
8.3 keV
40 pC
X-ray properties: storage ring versus FEL
• Assume same energy bandwidth (~ 1eV)
• XFEL photons in 10 fs = ring undulator photons in 1 s
• XFEL photons are coherent
LCLS:
the world’s first x-ray free electron laser
Injector
electron beam
1km linac 14GeV
AMO
SXR
Undulator hall
XPP
Near-hall: 3 stations
XCS
x-ray beam
CXI
Far-hall: 3 stations
MEC
LCLS X-ray Facilities
Near Experimental Hall
AMO
SXR
XPP
X-ray Transport Tunnel
200 m
Start of
operation
AMO
Oct-09
SXR
May-10
XPP
October-10
CXI
February-11
XCS
November-11
MEC
April -12
XCS
CXI
MEC
Far Experimental Hall
LCLS instruments and their focus
• AMO: Atomic, Molecular and Optical Science
Multi-Photon processes within atoms and molecules
• SXR: Soft X-ray Research
Electronic and magnetic properties of materials and surfaces
• XPP: X-Ray Pump Probe
Atomic and electronic dynamics after optical excitation
• CXI:
Coherent X-Ray Imaging
Single shot imaging of atomic and nanostructures (mostly biology)
• XCS: X-Ray Correlation Spectroscopy
Atomic scale equilibrium dynamics in condensed matter systems
• MEC: Matter in Extreme Conditions
Properties far, far from equilibrium
X-Rays can see the invisible
--provide static and dynamic information--
“Imaging”
Photoemission
X-ray absorption
X-ray emission
Diffraction
EXAFS
X-ray magnetic dichroism
spin pol. photoemission
Understanding the function of today’s devices with SSRL/ALS
and tomorrow’s speed limits with LCLS
ALS work has revealed how most advanced magnetic devices switch today
0
200ps
100 nm
SSRL
LCLS
400ps
600ps
800ps
1 ns
X-FEL Science
or
The Need for Speed !
The speed of things – the smaller the faster
macro
molecules
molecular
groups
atoms
“electrons”
& “spins”
The technology gap
optical laser pulse
What determines the speed of things?
rule of thumb…“the smaller the faster”….
• but the devil is in the details…
• mechanical “speed” of motion related to concept of inertia or mass
(more massive being “bigger”)
F = m a …. p = m v
• “speed” also dependent on the process
conservation laws govern dissipation of energy, linear and angular momentum
e.g. friction, induction, torque
• detailed correlation depends on system and process of interest
Understanding of motion and speed essential for “function”
Characteristic speeds of atoms, electrons and spins
• Atoms :
speed of sound:
1 nm / 1 ps
• Electrons:
Fermi velocity:
1 nm / 1 fs
• Light:
speed of light:
1 nm / 3 as
The new science paradigm:
Static nanoscale “structure” plus its dynamic “function”
Operational
Timescales
Fundamental
Timescales
The world of x-rays
nanoscale dynamics
smaller & faster
Important areas in ultrafast science
Because of their size, atoms and “bonds” can change fast
but how do systems evolve? key areas of interest:
equilibrium
(“structure”, phase diagram of a system T, P …)
close to equilibrium
(operation or function of a system, e.g. current flow)
far from equilibrium
(transient states after excitation, e.g. chemical reaction)
far-far from equilibrium
(transient states after extreme stimulus, e.g. a plasma)
The new paradigm in understanding atomic matter
Function and Control
Structure and Properties
Nanoscale order
Dynamic order
Transient States
Long range order
Static disorder
Equilibrium States
1900
• most reliably calculated
2000
future
• difficult to measure and calculate
“Equilibrium”: What is the structure of water?
Small angle x-ray scattering shows inhomogeneity
Disordered soup
Ice like clusters
Components probably dynamic – form and dissolve
- can we take an ultrafast snapshot??
A new Paradigm in Macromolecular Crystallography
“beating the speed of sound with the speed of light”
conventional method
Protein crystal
Diffraction data
Electron density
Molecular model of protein
suggests its function
In 1980s synchrotron x-rays revolutionized macromolecular crystallography
• Protein structure has allowed the developments of drugs
• However, synchrotron studies limited to large (> 5 microns) crystals
• Data for smaller crystals limited by x-ray beam damage
Studies of nanocrystals at X-FELs leads to a new paradigm
“Close to equilibrium” – how does a device function:
e.g. how does a spin current turn the magnetization ?
magnetic switching today
100nm size in 100ps - the speed of sound
how fast can it be done?
“bit”
in cell
100 nm
Computer chip
Electronic circuit
Memory cell
Magnetic structure of “bit”
“Far from equilibrium”:
How does a chemical reaction proceed?
reaction dynamics & intermediates
end reaction products
What are the key intermediate reactive species?
“Far, far from equilibrium”:
Warm and hot dense matter
The properties of matter in extreme states
- which on earth can only be created transiently on ultrafast time scaleAl r-T phase diagram
What have we learned so far?
Multi-Photon processes within atoms and molecules observed
- Provides new spectroscopic signatures – first non-linear effects
- LCLS can drive atom-based x-ray laser
• Concept of “probe-before-destroy” works for atomic structure
- Opens the door for atomic imaging of crystalline and disordered systems
- Small protein crystals studied to < 2 Å resolution
- 3D imaging of cells/viruses with nanoscale resolution appears possible
- atomic structure of liquids has begun
• Single shot study of electronic structure of solids & surfaces is possible
-“probe before destroy” also works, but electronic structure responds faster
fluence limits apply because of fast (e.g. stimulated) electronic processes
- Surface science studies show proof-of-principle capture of reactive states
- Laser pump/x-ray probe studies have seen time resolved melting of
electronic and spin structure and chemical transformations
LCLS in the future
soft x-ray
hard x-ray
LCLS today
The end
User Input at Workshop
• Atoms = electronic cores move slow enough (inertia) that
“probe before atomic motion” concept works
future vision:
 Maximum intensity for signal-to-noise – seeding, Terawatt beams
 Short pulse length (< 10 fs) to minimize effects of atomic motion
 Pursue first killer application: Bio-structures of small crystals
 Extend to single macromolecule imaging - requires TW beams < 5keV
• Electrons respond faster, take advantage of non-linear phenomena
future vision:
 Control photon energy, pulse intensity and shape – seeding
 Control polarization to distinguish charge & spin
 Explore x-ray/electronic interactions with controlled pulses
 Develop x-ray beam manipulation toolbox for non-linear x-ray optics
The trick to taking ultrafast pictures
-- our cameras are too slow--
• Use a bright flash, faster than existing shutter speed
• Capture bright “scattered” light flash with camera
leave shutter open, flash light is stronger than background light
flash
X-rayultrafast
Laser
1/20,000
fast (fs), intense,
shortsecond
wavelength
shutter speed
X-rayslow
Detector
1/200 second
slow (microseconds)
flash duration and intensity determine picture quality
x-rays can see “the invisible” nanoscale
Future Plans: LCLS-II and LUSI-II
hard x-ray
soft x-ray
LCLS II:
 builds the foundational facilities for enhanced capabilities and capacity
 first step to remain at the international forefront
LUSI II:
 adds science driven instrumentation to LCLS II baseline
 may include source refinements, optics enhancements, end stations
5 things LCLS may become known for
• Motion pictures of the formation and dissociation of chemical bonds
viewed at the site of selected atoms
• Solving the structure and time-resolved function of non-periodic
macromolecular complexes (e.g. proteins)
• Solving the (transient) structure of disordered systems, e.g. water
• Characterizing the nature of transient states of matter created by
radiation, pressure, fields, etc.
• Revealing the origins of fundamental speed limits of technological
processes
LCLS-II science example 1:
Studies of carbon related reactions become possible
Carbon spectra of molecules
Conversion of chemicals
Clean fuel
The key challenge:
• Understand/control of the transient reactive state
• “where the action is”
Slide 41