Transcript Document 7373299

Overview of laser,
timing, and
synchronization issues
John Corlett, Larry Doolittle, Bill Fawley, Steven Lidia,
Bob Schoenlein, John Staples, Russell Wilcox, Sasha
Zholents
LBNL
John Corlett, July 2004
Scientific goal - application of ultrafast x-ray
sources to study dynamics with high-resolution
• Diffraction and spectroscopy
• Nuclear positions and electronic, chemical or structural probes
Time-resolved
x-ray diffraction
detector
diffraction angle
time delay
Time-resolved
EXAFS
NEXAFS
f(r)
absorption
r
delay
K edge
energy
Plus photoelectron spectroscopy, photoemission microscopy, etc
• Access new science in the time-domain x-ray regime
John Corlett, July 2004
Pump-probe experiment concept
Laser excitation pulse
sample
∆t
g-detector
ion or edetector
X-ray probe pulse
• Ultrafast laser pulse “pumps” a process in the sample
• Ultrafast x-ray pulse “probes” the sample after time ∆t
• Ultrafast lasers an integral part of the process
• X-rays produced by radiation in an electron accelerator
John Corlett, July 2004
Pump-probe experiment concept
Laser excitation pulse
sample
∆t
g-detector
ion or edetector
X-ray probe pulse
• Both laser and x-ray pulses should be stable in temporal and spatial
distributions
• Parameters and quality of x-ray pulse determined by the electron beam
• Accelerator parameters
• Synchronization between laser and x-ray pulses, ∆t, should ideally be known
and controllable - to the level of the pulse duration itself ~ 10 fs
John Corlett, July 2004
Many projects around the world are addressing the need
for ultrafast x-rays, in different ways
•
•
•
•
LCLS: linac SASE (construction)
BNL DUV FEL: linac HGHG (operational)
DESY TTF-II: linac SASE (construction)
SPPS: linac spontaneous emission from short bunches (operational)
•
•
•
•
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•
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•
•
ALFF: linac SASE
BESSY FEL: linac HGHG
European X-ray FEL: linac SASE
Daresbury 4GLS: ERL HGHG + spontaneous
LUX: recirculating linac HGHG + spontaneous
Cornell ERL: ERL spontaneous
MIT-Bates X-ray FEL: linac HGHG + SASE
Arc-en-Ciel: recirculating linac / ERL HGHG + SASE
FERMI@Elettra: linac HGHG
BNL PERL: ERL spontaneous
John Corlett, July 2004
What are the difficulties in achieving x-ray beam
quality?
•
•
•
X-rays are produced by electrons emitting synchrotron radiation in an
accelerator
The electron beams are manipulated by rf and magnetic systems
The x-ray beam quality is limited by the electron beam quality in many ways
– Electron bunch charge, energy, emittance, energy spread, bunch length, position,
…
• At the radiator!
•
Production of high-brightness bunches is tough enough
•
Then we must accelerate and otherwise manipulate the bunches before they
reach the radiating insertion device
Many opportunities to degrade the electron bunch
•
– Emission process, space charge, rf focusing, ….
– Space charge, rf focussing, emittance compensation, CSR, geometric wakefields,
rf field curvature, resistive wall wakefields, optics aberrations, optics errors,
alignment, rf phase errors, rf amplitude errors, …
John Corlett, July 2004
Synchronization
•
In addition to the electron bunch properties, the need for synchronization
of the x-ray pulse to a reference signal - the pump - is required for many
experiments
– Time between pump signal and probe x-ray pulse
• Predictable or measurable
• Stable to ~ pump & probe pulse durations
•
This presents additional demands on the accelerator, instrumentation, and
diagnostics systems
•
Various techniques may be employed to enhance synchronization
– Slit spoiler for SASE
– Seeding
• HGHG
• ESASE (Enhanced SASE)
– e- bunch manipulation & x-ray compression
– Measurement of relative x-ray - pump laser timing
• Electro-optic sampling of electron bunch fields
• Time-resolved detection of x-ray and laser pulses at the sample
John Corlett, July 2004
The roles of lasers, timing,and synchronization in
an ultrafast x-ray facility
•
Laser systems
•
Timing system
•
Synchronization
– Generate the high-brightness electron beam in an rf photocathode gun
– Produce the pump signals at the beamline endstations
– Provides reference signals to trigger (pulsed) accelerator systems
– Provides reference waveforms to synchronize rf systems
– Provides reference waveforms to synchronize endstation lasers
– To control and determine the timing of the x-ray pulse with respect to a pump
pulse
– Requires stable systems in the x-ray facility, connected by a “stable” timing
system including stable timing distribution systems
• The timing system only has to be “stable” enough for all of the components connected to
it to follow it’s timing jitter (to the required level)
• Phase noise  timing jitter
2
• The majority of the timing jitter must be within the bandwidth of
&
2the
L(f accelerator
)df
f1
laser systems such that they can follow
t rms 
2f 0
– Local feedback around rf & laser systems
– Lock to timing system master oscillator
f
John Corlett, July 2004
Phase noise and timing jitter
f2
t rms 
2 L(f )df
f1
2f 0
John Corlett, July 2004
Some space and time parameters for a conceptual
ultrafast x-ray facility
Bend magnets / compressor
rf photocathode gun
Linac
Undulators
End stations
Length scale ~ 100’s m
Time scale ~ µs
Equivalent bandwidth ~ 100’s kHz
• 10 fs ≈ 3 µm at c
• Thermal expansion for ∆T = 0.1°C in Cu over 100 m
≈ 170 µm or 570 fs
• Similar magnitude effect from refractive index change in optical fiber
John Corlett, July 2004
Some rf systems parameters for a conceptual
ultrafast x-ray facility
Bend magnets / compressor
rf photocathode gun
Linac
Undulators
End stations
• 10 fs ≈ 5x10-3 °rf phase L-band
• Cavity filling time (Q=104) ≈ 2 µs
• Bandwidth ~ 100 kHz
• Cavity filling time (Q=107) ≈ 2 ms
• Bandwidth ~ 100 Hz
• 10 fs ≈ 1x10-2 °rf phase S-band
• Cavity filling time (Q=104) ≈ 1 µs
• Bandwidth ~ 300 kHz
John Corlett, July 2004
Synchronize rf systems to a master oscillator
• Noise sources
• Microphonics
• Thermal drift
• Electronic noise
• Digital word length
• Control phase and amplitude of the rf fields experienced by the electron
beam
• The master oscillator must have a phase noise spectrum such that the
majority of the timing jitter is accumulated within the bandwidth of the rf
systems
• Local feedback ensures that the rf systems follow jitter in the master
oscillator
John Corlett, July 2004
Choice of master oscillator
• rf crystal oscillator has low noise close to carrier
• Laser has low noise above ~ 1 kHz
• Mode locked laser locked to good crystal oscillator provides a suitable
master oscillator
• Active mode-lock cannot respond rapidly to perturbations
John Corlett, July 2004
Although there are very good low-noise sapphire
loaded cavity oscillators
http://www.psi.com.au/pdfs/PSI_SLCO.pdf
John Corlett, July 2004
Phase noise spectrum requirement
• Master oscillator phase noise within bandwidth of feedback systems can be
corrected
• Residual uncontrolled phase noise plus noise outside feedback systems
bandwidth results in timing jitter and synchronization limit
John Corlett, July 2004
Laser synchronization
D.J. Jones et al., Rev. Sci. Instruments, 73, 2843 (2002).
time (sec)
• two independent psec Mira 900-P (Coherent) lasers
• PLLs at 80 MHz (n=1) and 14 GHz (n=175)
• Sub-femtosecond timing jitter has been demonstrated between two modelocked Ti:sapphire lasers
• Limit is electronic noise (under favorable conditions)
John Corlett, July 2004
Sophisticated laser systems are an integral
component of an FEL facility
FEL seed lasers
Laser oscillator
Spatial
profiling
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Amplitude
control
Multiply
Amplifier
Pulse
shaping
Laser oscillator
Multiple beamline
endstation lasers
Photocathode laser
John Corlett, July 2004
Lasers may be synchronized to a common master
oscillator
FEL seed lasers
Laser oscillator
Spatial
profiling
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Amplitude
control
Multiply
Amplifier
Pulse
shaping
Laser oscillator
Laser master
oscillator
Multiple beamline
endstation lasers
Photocathode laser
John Corlett, July 2004
rf systems need to be synchronized to a common
master oscillator
FEL seed lasers
Laser oscillator
Spatial
profiling
Amplitude
control
Multiply
Amplifier
Pulse
shaping
Laser oscillator
~
Laser master
oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Multiple beamline
endstation lasers
Photocathode laser
John Corlett, July 2004
rf signals for the accelerator may also be derived
from the laser master oscillator
FEL seed lasers
~
Spatial
profiling
Laser oscillator
~
~
~
Amplifier &
conditioning
~
~
~
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Laser oscillator
Amplifier &
conditioning
Amplitude
control
Multiply
Amplifier
Laser master
oscillator
Pulse
shaping
Multiple beamline
endstation lasers
Laser oscillator
Photocathode laser
Accelerator RF signals
John Corlett, July 2004
rf photocathode gun
John Corlett, July 2004
rf photocathode laser
File: cc120605, RMS length = 1.07 ps
150
0.4
UV Power (V)
200
250
300
0.3
0.25
0.2
0.15
0.1
350
0 20 40 60 80100120140160
140
120
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80
60
40
20
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0.35
0.05
Vertical lineout
0
-3
-2
-1
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1
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Time (ps)
3
4
5
UV pulse time profile
250
300
350
400
450
Horizontal lineout
•
•
UV pulse on cathode
W. S. Graves, MIT-Bates (DUV FEL, Brookhaven)
John Corlett, July 2004
rf photocathode laser
600
Current (A)
UV Power (V)
0.4
0.35
0.3
0.25
400
300
100
0.15
Bunch
production,
acceleration,
and
compression
0.1
0.05
-2
-1
0
1
2
Time (ps)
3
4
5
UV pulse time profile
•
•
500
200
0.2
0
-3
File: phiminusg, FWHM = 0.474 ps
700
File: cc120605, RMS length = 1.07 ps
00
20
40
60
80
100
120
140
160
180
200
0.2
0.8
0.6
Time (ps)
0.4
1
Tail
50
1.2
1.4
Head
100
150
200
250
300
350
400
UV pulse on cathode
– Non-uniformity exacerbates space-charge effects
– Temporal non-uniformity induces micro-bunching
W. S. Graves, MIT-Bates (DUV FEL, Brookhaven)
John Corlett, July 2004
Laser pulse shaping influences the emitted
electron bunch
RF from
master
oscillator
Ti:sapphire
Oscillator
Q-switched
Nd:YAG (2w)
100 fs, 2 nJ
<0.5 ps jitter
grating
stretcher
Pulse
Shaper
Ti:sapphire
Regenerative
Amplifier
grating
compressor
2w,3w
>1 mJ, 800 nm, 10 kHz
photoswitch
Pulse Shaper (A.M. Weiner)
Pockels
Cell
polarizer
Deformable
mirror
Pulse Amplitude Stabilizer
Patent:: LLNL (R. Wilcox)
spectral filter (computer controlled)
- spatial light modulator
- acousto-optic modulator
Dazzler - FastLite Inc.
acousto-optic dispersive filter
(P. Tournois et al.)
TeO2 crystal
acoustic wave (computer programmable)
- spectral amplitude
- temporal phase
John Corlett, July 2004
Laser-driven photocathode - one of the
many laser systems
H. Tomizawa, JASRI
•
R. Cross, J. Crane, LLNL
Need high reliability
– Integrated systems
– “hot spare” system attractive
– Develop techniques for pulse shaping
John Corlett, July 2004
rf gun phase and amplitude
• Cathode
– Cs2Te
• Laser
–1 µJ, 35 ps, 10 kHz, 266 nm
– Spatial and temporal control to
provide low-emittance electron
bunches
• RF field
– 64 MVm-1 at cathode
•
•
•
•
LUX rf gun concept as an example
Assume 5% of bunch length (1 psec) jitter
Primary drivers are launch phase, cell 1 gradient and bunch charge
(laser intensity)
Assumed uncorrelated disturbances: three most significant parameter
tolerances are (rms values):
– Launch phase: 0.43 degree
– Cell 1 gradient: 1.4% variation
– Bunch charge: 36% variation
John Corlett, July 2004
Nominal LCLS Linac Parameters for 1.5-Å FEL
Single bunch, 1-nC charge, 1.2-mm slice emittance, 120-Hz repetition rate…
6 MeV
z  0.83 mm
  0.05 %
250 MeV
z  0.19 mm
  1.6 %
Linac-X
L =0.6 m
rf= -160
4.54 GeV
z  0.022 mm
  0.71 %
135 MeV
z  0.83 mm
  0.10 %
rf
gun
Linac-1
L 9 m
rf  -25°
Linac-0
L =6 m
...existing linac
DL-1
L 12 m
R56 0
21-1b
21-1d
X
Linac-2
L 330 m
rf  -41°
Linac-3
L 550 m
rf  -10°
21-3b
24-6d
25-1a
30-8c
BC-1
L 6 m
R56 -39 mm
SLAC linac tunnel
BC-2
L 22 m
R56 -25 mm
14.1 GeV
z  0.022 mm
  0.01 %
undulator
L =130 m
LTU
L =275 m
R56  0
research yard
(RF phase: frf = 0 is at accelerating crest)
P. Emma, SLAC
John Corlett, July 2004
Jitter Tolerance Levels in the LCLS
Jitter tolerance budget
for LCLS based on the
many sensitivities
X-band
X-
LCLS
…and test the budget with jitter simulations
z jitter = 14 % rms
rms t-jitter = 109 fs
Jitter simulation, tracking 105
particles 2000 times, where
each run is randomized in its 12
main rf-parameters according to
the tolerance budget
•
P. Emma, SLAC
John Corlett, July 2004
SASE FEL output
•
The SASE FEL process arises from noise
Saturation
Half way along undulator
Radiation intensity build-up along undulator
http://www.roma1.infn.it/exp/xfel/SaseXfelPrinciples/Sasexfelprinciples.pdf
John Corlett, July 2004
Slit spoiler defines radiating region of bunch
x, horizontal pos. (mm)
2.6 mm rms
0.1 mm (300 fs) rms
50 mm
Easy access to
time coordinate
along bunch
z, longitudinal position (mm)
LCLS BC2 bunch compressor chicane
(similar in other machines)
Paul Emma, SLAC
John Corlett, July 2004
Add thin slotted foil in center of chicane
BEFORE FOIL
1-mm emittance
AFTER FOIL
5-mm emittance
1-mm emittance
Paul Emma, SLAC
John Corlett, July 2004
Timing determination from Electro Optic sampling developing techniques at the SPPS
A. Cavalieri
Principle of
temporal-spatial correlation
single pulse
Line image
camera
EO xtal
analyzer
polarizer
Er
30seconds, 300 pulses:
width
z = 530 fs ± 56 fs rms
centroid
t = 300 fs rms
John Corlett, July 2004
ESASE - Enhanced Self-Amplified Spontaneous
Emission
Modulation
Acceleration
Bunching
SASE
70 as
A. Zholents - Wednesday
John Corlett, July 2004
Enhanced Self-Amplified Spontaneous Emission
70 as
P0 = 235 GW
With a duty factor = 40,
Paverage~ 6 GW
x-ray macropulse
• Each micro-pulse is temporally coherent and Fourier transform limited
• Carrier phase is random from micro-pulse to micro-pulse
• Pulse train is synchronized to the modulating laser
John Corlett, July 2004
Harmonic generation scheme coherent source of soft x-rays
Developed and demonstrated by L.-H. Yu et al, BNL
e- bunch
laser pulse
modulator
e-beam phase space:
bunching
chicane
Output
energy
Input
radiator
-
phase

n
-n
Energy-modulate e-beam in
undulator via FEL resonance with
coherent input radiation
In a downstream undulator resonant at
l0/n, bunched beam strongly radiates at
harmonic via coherent spontaneous
emission
Dispersive section strongly increases
bunching at fundamental wavelength
and at higher harmonics
L.-H. Yu et al, “High-Gain Harmonic-Generation Free-Electron Laser”, Science 289 932-934 (2000)
L.H. Yu et al., "First Ultraviolet High Gain Harmonic-Generation Free Electron Laser", Phys. Rev. Let. Vol 91, No. 7, (2003)
John Corlett, July 2004
Cascaded harmonic generation scheme
seed laser pulse
disrupted region
radiator
modulator
tail
modulator
radiator
head
Low e electron pulse
Unperturbed electrons
Delay bunch in micro-orbit-bump (~50 mm)
seed laser pulse
modulator
3rd - 5th
harmonic
radiator
modulator
3rd - 5th
harmonic
radiator
John Corlett, July 2004
User has control of the FEL x-ray output
properties through the seed laser
• OPA provides controlled optical seed for the free electron laser
Q-switched
Nd:YAG (2w)
Ti:sapphire
Oscillator
<100 fs, 2 nJ
<50 fs jitter
Ti:sapphire
Regenerative
Amplifier
grating
stretcher
grating
compressor
Optical
Parametric
Amplifier
>10% conv. efficiency
~1 mJ, 800 nm, 10 kHz
RF derived
from optical
from master
oscillator
Endstation synch.
• Wavelength tunable
–
190-250 nm
–
10-200 fs
• Pulse duration variable
• Pulse energy
–
10-25 µJ
–
10 kHz
laser seed pulse
e-beam
undulator
undulator
harmonic
undulator
x-ray
n undulator stages
• Pulse repetition rate
• Endstation lasers seeded by or synchronized to Ti:sapphire oscillator
– Tight synchronization <20 fs
John Corlett, July 2004
Seeding with XUV from high harmonics in a gas jet
(HHG)
• Coherent EUV generated up to ~ 550 eV
– R. Bartels et al, Science 297, 376 (2002), Nature 406, 164 (2000)
Gas jet
Harmonic emission
67.5eV
25.5eV
E field
0
5
10
15
20
Time(fs)
25
30
I. Christov et al, PRL 78, 1251, (1997)
H. Kapteyn, JILA/Uni. Colorado/NIST
45 39
29
25
17
Harmonic order
J. Zhou et al, PRL 76(5), 752-755 (1996)
John Corlett, July 2004
Seeding multiple cascades from a single electron
bunch allows 10 kHz operation in LUX concept
FEL optical pulses
e-beam
• Optical pulses overlap different part of bunch for each beamline
• Timing jitter influences number of cascades that can be served by a
single bunch
• CSR effects in the arcs introduce ~ few fs jitter for ~ few % charge
variation
John Corlett, July 2004
Laser-manipulation produces attosecond
x-ray pulses in harmonic cascade FEL
800 nm
spectral
broadening and
pulse compression
e-beam
e-beam
harmonic-cascade FEL
2 nm modulator
two period wiggler tuned
time delay for FEL interaction at
chicane
800 nm
2 nm light from FEL
1 nm
coherent
radiation
chicane-buncher
1 nm radiator
dump
end
station
end
station
A. Zholents, W. Fawley, “Proposal for Intense Attosecond Radiation from
an X-Ray Free-Electron Laser”, Phys. Rev. Lett. 92, 224801 (2004)
John Corlett, July 2004
Ultrafast x-ray pulses by electron bunch
manipulation and x-ray compression
RF deflecting cavity
Electron trajectory
in 2 ps bunch
~ 50 fs
2 ps
John Corlett, July 2004
Synchronize deflecting cavities and pump laser for
hard x-ray production
RF
crab cavity
3.9 GHz
Master Oscillator
Laser
x-ray pulse
compression
asymmetric
Bragg x-tals
laser pulse
y
Low-noise
Amp
3.9 GHz
x-rays
electron bunch
t
t
t
y
• Synchronization dependent on phase of deflecting cavity
• Phase lock to master oscillator
• Fast feedback systems around scrf
• Extend frequency response of the system
John Corlett, July 2004
Typical end station concept
Precisely timed laser and linac x-ray pulses
Linac x-ray
pulse
Laser master
oscillator pulse
End station
Laser and
delay lines
Pulse diagnostics
~ 10 m
• Active laser synchronization
– Independent oscillators at each endstation
– Complete independence of endstation lasers
– Wavelength, pulse duration, timing,
repetition rate etc.
Modelocked
Oscillator
John Corlett, July 2004
Beamline endstation lasers
chirped-pulse amplification
Q-switched
Nd:YAG (2w)
Ti:sapphire
Oscillator
<100 fs, 2 nJ
<50 fs jitter
RF derived
from optical
master
oscillator
Ti:sapphire
Regenerative
Amplifier
grating
stretcher
grating
compressor
Optical
Parametric
Amplifier
>1 mJ, 800 nm, 10 kHz
typical regenerative amplifier
PC
l/4
PC
~20 passes  L=1 µm (t=66 fs)
• interferometric stabilization
• cross-correlate with oscillator (compress first)
• temperature stabilize (Zerodur or super-invar)
John Corlett, July 2004
All-optical timing system to achieve synchronization
between laser pump and x-ray probe
• Laser-based timing system
• Stabilized fiber distribution system
• Interconnected laser systems
Master Oscillator
• Active synchronization
Laser
• Passive seeding
• rf signal generation
 20–50 fs synchronization
FEL
Seed Laser
RF cavity
Optical fiber distribution network
FEL
Seed Laser
Multiple
Beamline Endstation
Lasers
Linac RF
Photo Injector
Laser
John Corlett, July 2004
Timing distribution
Master
Oscillator
cw reference laser
interferometer
position
detector
position
detector
free-space system (in vacuum)
Beamline 1
Beamline 2
Master
Oscillator
EDFA
(fiber amp)
cw reference laser
interferometer
Path Length Control
Agilent 5501B
L= 2 mm
210-9 one hour (l/l)
t= 7 fs
-8
210 lifetime
L~100 m
PZT control
path length
fiber-based system
EDFA
(fiber amp)
Beamline 1
Beamline 2
John Corlett, July 2004
Timing distribution - fiber systems developed fro
distribution of frequency standards
6
4
)
1/2
Jitter spectral density (fs / Hz
2
3
1
8
2
6
4
D. Jones, UCB/JILA
6
5
4
Integrated jitter
10
2
6
5
4
0.1
3
8
6
Integrated jitter (fs)
Mixer/amplifier
noise floor
100
4 km DSF in lab, unstabilized
4 km DSF in lab, stabilized
2
4
1
2
10
1
10
2
10
3
10
4
10
5
10
6
10
7
Fourier Frequency (Hz)
Master
Oscillator
EDFA
(fiber amp)
cw reference laser
interferometer
Path Length Control
Agilent 5501B
-9
L= 2 mm
210 one hour (l/l)
t= 7 fs
210-8 lifetime
L~100 m
PZT control
path length
fiber-based system
EDFA
(fiber amp)
Beamline 2
Beamline 1
John Corlett, July 2004
Modelocked fiber laser oscillator
rf stabilized
Modelocked Fiber Laser Oscillator – RF Stabilized
17 dBm mixer
RF Clock
1.3/n GHz
1/Trep
f
BPF 1.3 GHz
28 dB AMP
LPF
Trep
Amplifier
Modelocked Laser
1.3 GHz
error signal
• Phase-lock all lasers to master oscillator
• Derive rf signals from laser oscillator
• Fast feedback to provide local control of accelerator rf systems
 Synchronization 10’s fs
John Corlett, July 2004
Summary
Lasers, timing,and synchronization
• Laser systems under development at many institutions
• Applications for improved light-source operations
• Photocathode laser, timing system master oscillator, FEL seed
laser, endstation pump laser
• Manipulation of e- beam by laser has great potential
• HHG power increasing, wavelength decreasing
• Ultra-stable timing systems with optical fiber distribution systems
under development
• Application of techniques to accelerator environments and
requirements is to be demonstrated
• 10’s fs synchronization seems achievable
John Corlett, July 2004