LUSI XPCS Status
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Transcript of LUSI XPCS Status
LUSI XPCS Status
Team Leader: Brian Stephenson (Materials Science Div., Argonne)
Co-Leaders: Karl Ludwig (Dept. of Physics, Boston Univ.),
Gerhard Gruebel (DESY)
Sean Brennan (SSRL)Steven Dierker (Brookhaven)Eric Dufresne (Advanced Photon Source, Argonne)Paul Fuoss (Materials Science Div., Argonne)Randall Headrick (Dept. of Physics, Univ. of Vermont)Hyunjung Kim (Dept. of Physics, Sogang Univ.)Laurence Lurio (Dept. of Physics, Northern Illinois Univ.)Simon Mochrie (Dept. of Physics, Yale Univ.)Larry Sorensen (Dept. of Physics, Univ. of Washington)Mark Sutton (Dept. of Physics, McGill Univ.)
LCLS SAC Meeting June 7-8, 2006
Scientific Impact of X-ray Photon Correlation Spectroscopy at LCLS
New Frontiers:
• Ultrafast
• Ultrasmall
Time domain complementary to energy domain
Both equilibrium and non-equilibrium dynamics
Unique Capabilities of LCLS for XPCS Studies
Higher average coherent flux will move the frontier • smaller length scales
• greater variety of systems
Much higher peak coherent flux will open a new frontier • picosecond to nanosecond time range
• complementary to inelastic scattering
Wide Scientific Impact of XPCS at LCLS
•Simple Liquids – Transition from the hydrodynamic to the kinetic regime.
•Complex Liquids – Effect of the local structure on the collective dynamics.
•Polymers – Entanglement and reptative dynamics.
•Proteins – Fluctuations between conformations, e.g folded and unfolded.
•Glasses – Vibrational and relaxational modes approaching the glass transition.
•Dynamic Critical Phenomena – Order fluctuations in alloys, liquid crystals, etc.
•Charge Density Waves – Direct observation of sliding dynamics.
•Quasicrystals – Nature of phason and phonon dynamics.
•Surfaces – Dynamics of adatoms, islands, and steps during growth and etching.
•Defects in Crystals – Diffusion, dislocation glide, domain dynamics.
•Soft Phonons – Order-disorder vs. displacive nature in ferroelectrics.
•Correlated Electron Systems – Novel collective modes in superconductors.
•Magnetic Films – Observation of magnetic relaxation times.
•Lubrication – Correlations between ordering and dynamics.
transversely coherent X-ray beam
sample
XPCS using ‘Sequential’ Mode
• Milliseconds to seconds time resolution• Uses high average brilliance
t1
t2
t3
monochromator
“movie” of specklerecorded by CCD
g2 (t) I(t) I(t t)
I2
1
t
g2
1(Q) Rate(Q)
I(Q, t)
transversely coherent X-ray pulse from FEL
sample
XPCS at LCLS using ‘Split Pulse’ Mode
Femtoseconds to nanoseconds time resolutionUses high peak brilliance
sum of speckle patternsfrom prompt and delayed pulses
recorded on CCD
I(Q,t)
splitter
variable delay t
t
Con
tras
t
Analyze contrastas f(delay time)
10 ps 3mm
transversely coherent X-ray beam
sample
XPCS of Non-Equilibrium Dynamics using ‘Pumped’ Mode • Femtoseconds to seconds time resolution• Uses high peak brilliance
before
t after pumpmonochromator
Correlate a speckle pattern from before
pump to one at some t after pump
Pump sample e.g. with laser, electric, magnetic pulse
transversely coherent X-ray pulse from FEL
sample
‘Split Pulse - Sequential’ Mode: Crossed Beams
Femtoseconds to nanoseconds time resolutionUses high peak brilliance
Crossed beams at sample allows recording of separate speckle
patterns from prompt and delayed pulses (SAXS from 2-D samples)
I(Q, t2)
splitter
variable delay t
10 ps 3mm
g2(t) I(t1) I(t2)
I2
1
t
g2
1(Q) Rate(Q)
I(Q, t1)
Design of Experiments
Driven by analysis of sample heating by beam
For these studies of dynamics, we must avoid changing the behavior of the sample by the beam (e.g. < 1K heating)
Sample Heating and Signal Level
Maximum tolerable photons per pulse due to temperature rise:
NMIN 2 A E2abs
h2c2 el Mcorr
NMINSPECKLE
NMAX 3kBA
Eabs
TMAX
Minimum required photons per pulse to give sufficient signal:
Is there enough signal from a single pulse?Is sample heating by x-ray beam a problem?
NAVAIL f (E,E, A)
Maximum available photons per pulse:
See analysis in LCLS: The First Experiments
Heating and XPCS Signal from Single Pulse
See analysis in LCLS: The First Experiments
Shaded areas show feasibility regions e.g. for liquid or glass (green) or nanoscale cluster (yellow)
Detector SpecificationsPixel Size, Noise Level,
Number of Pixels, Efficiency
Speckle: negative binomial distrib.
Mean counts per pixel
Inverse contrast M
Probability of k counts:
Pk (k M)
(M)(k 1)1
M
k
k
1k
M
M
k
Low count rate limit
k 0.01
P1 k
1/ M 2P2 /P12 1
Optimum pixel size: ~1 ‘speckles’
Required Ntot (number of pixels at “same” Q): 106 to 108
P2 M 1
2Mk
2
Required signal/noise: determine P2 to a few %;
need N2 ~ Ntot k2 > 1000
Current Detector Questions1) In order to get large number of pixels, need to understand trade-offs between number of pixels, pixel size, noise level, efficiency, cost
Can an inexpensive commercial technology be adapted?
2) For XPCS, pixels do not have to be contiguous.
Using a mask to separate pixels could be a flexible way to produce small pixels, and reduce noise due to charge sharing between pixels
Beam Size at Sample
Larger gives less heating per total signal, but size limited by ability to resolve speckle pattern in reasonable sample-to-detector distance
Beam size = pixel size = speckle size = d = (L)1/2
For L = 5 m, get
d = 20 microns, 8 keV; d = 12 microns, 24 keV
Unfocused beam size at 8 keV is ~400 microns
Can use large coherent beam to
- split beam spatially to produce time delay
- doing heterodyne detection using reference beam
- feed another experiment
Conceptual Design: Mono and Splitter
Si (220) or C (111) energy resolution typ., 6-24 keV
Pulse splitter - 3 concepts:
• Partially-transmissive reflection e.g. Laue
• Split energy spectrum
• Split spatially (should be ~100 m upstream to combine at minimum angle)
For times longer than ~1 ns, should consider two pulses in linac
Mono upstream of splitter would remove heat load and avoid any effect of first pulse on second
Conceptual Design: Beamline Layout
Hutch in far hall
10 m long by 10 m wide hutch, with slits upstream; for SAXS region, 15 m long would be more flexible
Need very low background (mirror system in front end will solve)
Concerned about stability of upstream optics (need 0.5 microradian)
Either no focusing or moderate (up to 1:1), compound refractive lenses in upstream tunnel
Pumped mode experiments will require synchronized lasers
Sample
Detectors
Hutch
FocusingOptics
Horiz. offsetmonochromator
PulseSplitter
Defining apertures
Transmitted Beam 15-20 m
Conceptual Design: Beamline Layout
Far exp. hall
~100 m
10 m
Large Offset Monochromator
XPCS requires monochromator
Mono offset can be used to separate beams, eliminate 'flipper' mirrors
Transparent first crystal could allow simultaneous operation of other station(s)
Goniometer and Sample Chambers
Plan 3 different chambers for different T regions
Flight paths and detector supports require thought
Summary of R&D Needs, Sub-Teams
• Detector and Algorithm (Lurio, Mochrie)
• Split/Delay (Gruebel, Stephenson)
• Beam Heating of Sample (Stephenson, Ludwig)
• Large Offset Mono (Stephenson, Gruebel)
• Goniometer and Sample Chamber (Ludwig, Sutton)
Multilayer Laue Lenses: A Path Towards One-Nanometer Focusing of Hard X-rays
H. C. Kang, G. B. Stephenson, J. Maser, C. Liu, R. Conley, S. Vogt, A. T. Macrander (ANL)
Multilayer Laue Lens Deposition of thick, graded multilayer at APS; sectioning and microscopy at MSD/EMC/CNM.
Electron microscopy shows accuracy of layer spacings
Theory
An ideal Multilayer Laue Lens should focus X-rays to 1 nm with high efficiency.
Experiments
We have fabricated partial MLLs and measured their performance. The results support the predictions of theory.
WSi2/Si, 728 layers
12.4 m thick
r~10 nmr~58 nm
Nearly diffraction-limited performance of test structures
30 nm FWHM, 44% efficiency, 0.06 nm wavelength
H.C. Kang et al, Phys. Rev. Lett. 96, 127401 (2006)
-150 -100 -50 0 50 100 150
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1.0
Sample A Sample B Sample C Gaussian fit
Inte
nsity
(no
rmal
ized
)
X (nm)
Substrate
Graded-spacing Multilayer
Substrate
Graded-spacing Multilayer
Sub-20 nm Hard X-ray Focus
Section depth = 13.05 m, rmin=5nm, f=2.6 mm @APS 12BM
FWHM ~ 19.3 nm
E = 19.5 keV
~ 33 %