Lasing and Saturation of
the LCLS at 1.5 Å
Paul Emma, for the LCLS Commissioning Team
SLAC National Accelerator Laboratory
Aug. 23-28, 2009
UCLA
April 10, 2009
The Vision…
John Madey, 1971
“…possibility of partially coherent radiation sources in the … x-ray
regions to beyond 10 keV.”
Linac Coherent Light Source at SLAC
X-FEL based on last 1-km of existing 3-km linac
1.5-15 Å
(14-4.3 GeV)
See J. Galayda Talk
Injector (35º)
at 2-km point
Existing 1/3 Linac (1 km)
(with modifications)
New e- Transfer Line (340 m)
X-ray
Transport
Line (200 m)
Undulator (130 m)
Near Experiment Hall
UCLA
Far Experiment
Hall
Commissioning Status of LCLS
Laser, gun, & injector commissioned: 2007
Linac & bunch compressors commissioned: 2008
First beam through undulator beamline: Dec. 13, 2008
21 undulator magnets installed & ready: April 7, 2009
First lasing at 1.5 Å: April 10, 2009 (first try!)
1.5 Å FEL saturation observed: April 14, 2009 (after BBA)
X-ray diagnostics commissioned July 1 – now (not done)
Soft x-rays transported into hutch #1 (AMO) Aug. 18, 2009
User operations start Oct. 1, 2009 (commission in Sep.)
132 meters of FEL Undulator Installed
All 33
undulators
now installed !
H.-D. Nuhn, THOA02
July 22, 2009
First Attempts at FEL Lasing – April 10, 2009…
21 undulator magnets installed (slots 13-33)
Reduce peak current to 500 A (normally 3000 A)
Observe screen 50 meters past undulator (FEE
diagnostics not ready until late June)
Insert one undulator magnet at a time. Correct orbit,
check field integrals, & spontaneous radiation pattern
J. Welch, THOA05
After 10 undulators inserted, we begin to see a
smaller spot at center of screen (still 500 A)
So we insert 12 undulators and then slowly raise the
peak current back to 3 kA…
1.5 Å
FEL light!
Undulator Gain Length Measurement at 1.5 Å: 3.3 m
gex,y  0.4 mm (slice)
Ipk  3.0 kA
sE/E  0.01% (slice)
(25 of 33 undulators installed)
D. Ratner, TUOA03
FEL e- Energy-Loss Shows >2 mJ per X-ray Pulse
1.5 Å
Also monitor
and calibrate
gas detector
readings
10 MeV/e- (2.4 mJ)
initial DEi
Dumpline
BPMs
 ~100 meters 
Horizontal
DE = DEf - DEi
Dog-Leg
BPMs
vary FEL power with oscillations & record e- energy loss
Vertical
Bend
final DEf
FEL Intensity Jitter 9.6% rms at 1.5 Å over >1 hr
> 1 hr
klystron trips
1.87 ± 0.18 mJ
30 Hz beam rate,
5 Hz sample rate,
10000 data points,
SASE saturation
Injector Transverse Projected Emittance ~0.5 mm
Exceptional beam
quality from S-band
Cu-cath. RF gun…
Time-sliced x-emittance: 0.4 mm
gex  0.43 mm
135 MeV
0.25 nC
35 A
gey  0.46 mm
D. Dowell, et al.
J. Wu, TUPC56
LCLS Machine Layout
L0 TCAV0
heater
3 wires
3 OTR
L1X
3 wires
2 OTR
3 OTR
L1S
sz1
L2-linac
DL1
BC1 stopper
135 MeV 250 MeV
sz2
4 wire
old
scanners
screen
+ 8 coll’s
4 wire
scanners
+ 6 coll’s
m wall
gun
BC2
TCAV3 L3-linac BSY
DL2
4.3 GeV 5.0 GeV
14 GeV 14 GeV
vert.
stopper dump
undulator
14 GeV
Accelerator is last 1-km of SLAC linac (14 GeV)
RF photocathode gun and off-axis injector
Two bunch compressors + ‘laser heater’
Two transverse RF deflectors for time-resolved beam measurements
X-band (12 GHz) compression linearizer
4 emittance diagnostic stations + 4 spectrometers
Primary and secondary collimation sections
Fixed gap, planar, 132-m undulator at 14 GeV + 1-mm res. RF BPMs
Near and Far Experimental Halls + 500 m of x-ray transport
YAGS2
RF deflector ON
energy
time
Laser OFF
σE/E < 12 keV
YAGS2
adds Landau damping
Laser Heater
Working Well
Z. Huang, WEOA01
Laser: 40 µJ
σE/E  45 keV
YAGS2
Laser: 230 µJ
σE/E  120 keV
Laser Heater Improves FEL Power & Gain Length
nominal (6 mJ)
D. Ratner, TUOA03
33 undulators & some
YAG saturation?
Laser heater OFF
Heater OFF
0.01% at 14 GeV with
compression factor 90
1.5 Å
0.4-mm emit
0.5-mm emit
Heater OFF
Heater ON
Undulator Girder with 5-DOF Motion Control + IN/OUT
Beam Finder Wire (BFW)
Cavity BPM (<0.5 mm)
Quadrupole
magnet
3.4-m
undulator
magnet
sand-filled,
thermally
isolated
supports
J. Welch, TUPC53
X-translation
(in/out)
Wire Position
Monitor
H.-D. Nuhn, THOA02
Hydraulic Level
System
CAM-based
5-DOF
motion
control
Beam-Based Undulator Alignment
H. Loos
Measure undulator trajectory at 4 energies (4.3, 7.0, 9.2, & 13.6 GeV)
Scale all linac & upstream transport line magnets each time
Do not change anything in the undulator
Calculate… (Matlab GUI)
Move quads and adjust BPM offsets for dispersion free trajectory
Iterate…
H.-D. Nuhn, THOA02
RESULT: vary energy by factor of 3  trajectory changes by <10 mm
Undulator Quadrupole Alignment after BBA
Vary each quadrupole magnet gradient by 30% sequentially
Record kick angle using both upstream & downstream BPMs,
adjusting for incoming jitter
Calculate quadrupole magnet transverse offsets
Earth’s field effect (0.4 G)
8 mm rms
undulators installed (with m-metal)
Z (m)
<1 mm Undulator Quadrupole Remote Position Control
3-parameter fit
to 20 BPMs
along undulator
(y0, y0, and Dy)
Dy = 30 nrad kick due to quad
±4 mm
(y0, y0)
0.7 mm
backlash
<0.5 µm res.
Thanks ANL!
Undulator Alignment Diagnostics (Stretched Wires & Hydraulic Levels)
Measured und. & quad moves
H.-D. Nuhn, THOA02
6
x [microns]
4
undulator alignment
drift over 3 days
Calculated orbit change
2
0
-2
-4
-6
0
5
10
15
20
Girder Numbers
25
30
35
Undulator Taper more than Doubles Power
1.5 Å
measured range (|x|  5 mm)
Wake (3 kA)  40 MeV
Spont. (13.6 GeV)  20 MeV
Post Sat. Taper  70 MeV
1%
5-mrad pole
cant angle
unmeasured range (>5 mm)
H.-D. Nuhn, THOA02
Electron Energy Loss & Spread Induced by FEL Gain
FEL OFF
FEL
FELOFF
ON
Undulator, Dump-Line, and Screen
4.3 GeV, lr = 15 Å, Ipk = 500 A
0.05%
allow FEL FEL
with with
straight
orbit
suppress
oscillation
2.6 mJ @
830 eV
50 MeV
FEL ON
10 MeV
loss/e-
Longitudinal Wakefields in the LCLS Undulator
±4 MeV
3.0±0.3 kA
Sasha Novokhatski, WEPC22; and J. Wu, WEPC24
Measured 1.5-Å FEL Attenuation of Be Solid Attenuators
9 Be Attenuators (0.01-32 mm)
Be Attenuator
Gas Detector
(1 Torr)
Log-e (gas-detector)
Attenuation length = 3.73 ± 0.08 mm (8.3 keV)
Measurements and Simulations for 20-pC Bunch at 14 GeV
MEASURED SLICE EMITTANCE
20 pC
135 MeV
gex = 0.14 µm
20 pC tested
J. Frisch,
WEOD01
time-slicing at 20 pC
Y. Ding
PRL 102 854801
SIMULATED FEL PULSES
1.5 Å,
3.61011
photons
Ipk = 4.8 kA
ge  0.4 µm
Y. Ding
Z. Huang
Simulation at 1.5 Å based on measured injector &
linac beam & Elegant tracking, with CSR, at 20 pC.
15 Å,
2.41011 photons,
Ipk = 2.6 kA,
ge  0.4 µm
Y. Ding
Z. Huang
1.2 fs
Simulation at 15 Å based on measured injector &
linac beam & Elegant tracking, with CSR & 20 pC.
First Experiment Has Started Commissioning (AMO)
Soft X-Ray Mirror
Transport Done
Atomic, Molecular, and
Optical Science (AMO)
Atomic, Molecular, and Optical Science (AMO)
This instrument, designed for photons in the 0.8-2.0 keV range, will investigate the effects of the x-ray beam on atoms and
molecules: absorption, ionization and subsequent evolution of the electronic structure on femtosecond time scales, and also
to investigate the behavior of atoms in excitation states previously impossible to study (e.g., stripped of all K-shell electrons).
Problems & Issues
X-ray diagnostics installation & commissioning fell
behind schedule (1.5 months)
X-ray spot size is a bit large for the present
mirrors (mis-calculation + technical limits)
120-Hz operation still requires much work (spring
or summer of 2010)
OTR screens beyond BC1 still unuseable (COTR)
Controls commissioning takes time
Many smaller issues that need attention:
Cavity BPM gain drift >20% over 1-2 weeks
No short-bunch (<10 fs) diagnostics
Energy change still requires up to 1 hr
Comments
Hard X-ray SASE FEL works, and works well
No blind tuning or unexpected settings required, with
lower charge preferred (0.25 nC)
FEL starts up quickly after 8-hr mainenance day and is, in
fact, difficult to suppress (up to 3.8 mJ observed at 1.5 Å)
These results are of course quite welcome, but are
somewhat surprising…
Many of us were expecting a more difficult struggle, as
was the case at the SLC, but this is just the start.
Acknowledgements
Thanks to…
The extraordinary commissioning team at SLAC !
The operations, metrology, engineering, controls,
installation, and RF groups at SLAC
The tremendous undulator and cavity-BPM team
at ANL
The x-ray diagnostics team at LLNL
John Galayda (project director) for his leadership
and confidence in the team
And many of you, who have contributed your
ideas, comments, and many years of experience
toward this revolutionary new light source, 17 yrs
after it was first proposed