1. Commissioning Status of the LCLS Accelerator and Undulator Systems
Henrik Loos
for the LCLS Commissioning Team

2. Accelerator Commissioning
Overview
LCLS Introduction
Accelerator Commissioning
Emittance
Laser Heater
Bunch Compression
Feedback
Stability
Undulator Commissioning
Diagnostics
Beam Based Alignment
Spontaneous Radiation
Outlook

3. Linac Coherent Light Source at SLAC
X-FEL based on last 1-km of existing linac
Injector (35º)
at 2-km point Å
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
Far Experiment
Hall

4. LCLS Accelerator Layout
6 MeV
z  0.83 mm
  0.05 %
135 MeV
z  0.83 mm
  0.10 %
250 MeV
z  0.19 mm
  1.6 %
4.30 GeV
z  mm
  0.71 %
13.6 GeV
z  mm
  0.01 %
beam parked here
Linac-X
L =0.6 m
rf= -160
Linac-0
L =6 m rf
gun
L0-a,b
Linac-1
L 9 m
rf  -25°
Linac-2
L 330 m
rf  -41°
Linac-3
L 550 m
rf  0°
25-1a
30-8c
...existing
linac
21-3b
24-6d
21-1
b,c,d
undulator
L =130 m X
BC1
L 6 m
R56 -39 mm
BC2
L 22 m
R56 -25 mm
undulator
DL1
L 12 m
R56 0
DL2
L =275 m
R56  0
Commission Mar-Aug 2007
Commission Jan-Aug 2008
Dec 2008…
SLAC linac tunnel
research yard
X-rays in spring 2009

5. LCLS Beam Diagnostics 2 Transverse RF cavities (135 MeV & 5 GeV)
BC2
4.3 GeV
BSY
14 GeV
TCAV3
5.0 GeV
BC1
250 MeV
L1S
3 wires
2 OTR
L1X
4 wire
scanners
L2-linac
L3-linac
DL1
135 MeV L0
gun
TCAV0
old
screen
3 OTR
sz1
sz2
stopper
heater
m wall
DL2
undulator
scanners +
4 collimators
vert.
dump
2 Transverse RF cavities (135 MeV & 5 GeV)
~195 BPMs and toroids
7 YAG screens (at E 135 MeV)
12 OTR screens at E  135 MeV
15 wire scanners (each with x & y wires)
CSR/CER pyroelectric bunch length monitors at BC1 & BC2
4 beam phase monitors (2856 – 51 MHz)
Gun spectrometer line + injector spectrometer line
YAG screens
OTR screens
Wire scanners

6. Injector Emittance Commissioning
Measured emittance meets requirement for FEL
Emittance measured at OTR screen with upstream quad scan
for 95% charge
Q = 250 pC
E = 135 MeV
Iterative Optimization with gun solenoid & quads, steering correctors, and matching to design Twiss
γεx = 0.83 μm
For 1 nC
γεx = 1.07 μm
γεy = 1.11 μm
γεy = 0.86 μm

7. New LTU Wire-Scanners Working Well
Emittance to upstream of undulator (mostly) preserved
Emittance horizontal 1.1um

8. Laser-Heater Working Well
YAGS2
Laser OFF
σE/E < 12 keV
RF deflector ON
time
energy
YAGS2
Laser: 40 µJ
σE/E  45 keV
Dec. 10, 2008
YAGS2
Laser: 230 µJ
σE/E  120 keV

9. Laser-Heater Working Well
YAGS2
YAGS2
Laser energy 230 µJ
σE/E  120 keV
Laser OFF
Double-horn is consistent with laser beam presently ~50% larger in transverse size than electron beam

10. Bunch Compression in BC2
Bunch Length vs. Compression
V0 ≤ 20 MV e- sz
2.44 m bc bp
D  90°
V(t) sy RF
‘streak’
S-band
Calibration
Measurement
Q = 0.25 nC
σz ≈ 2 μm

11. CSR Emittance Growth in BC2
Beam emittance can grow due to coherent synchrotron radiation effects during bunch compression
Compare measurements with simulation code
Confirms 100% projected emittance growth at nominal compression
Slice emittance not effected at operating point
Emittance growth mechanisms well understood
Y. Ding, Z. Huang

12. Laser & Electron-Based Feedback Systems
Transverse Loops Stabilize:
Laser spot on cathode
Gun launch angle
Injector trajectory
X-band cavity position
Linac & LTU trajectory (5)
Undulator trajectory
Longitudinal Loops Stabilize:
DL1 energy
BC1 energy
BC1 bunch length
BC2 energy
BC2 bunch length
Final energy L0
gun L3 L2 X
DL1
BC1
DL2 L1
sz1 d1 1 V1
sz2 d2 2 V2 d3 V3 d0 V0
D. Fairley, J. Wu
BC2
BPMs
CER detectors
Steering Loop
Laser

13. Feedback system keep machine stable for short-term …
LCLS Beam Stability
Injector
Beam position
Laser: 3%
Injector: 4% at 250 MeV
Linac: 10-15% at 9 GeV
Undulator: ~20%
Goal is 10%
Bunch length
BC1: 5% at 250 A
BC2: 8% at 3000 A
Charge & Energy
ΔQ/Q ≈ 1.5%
ΔE/E ≈ 0.03% at 13.6 GeV
1-s beam size
Linac
D. Ratner
Feedback system keep machine stable for short-term …

14. Electron Beam Reaches Brightness for 1.5 Å
… and for long-term!
FEL Power Prediction
3D Gain Length
Gain length and saturation power calculated from measured electron beam parameters

15. LCLS Undulator Configuration
In/Out
Scan
Beam
Undulator
Quad
RF BPM
Girder
BFW
Corr
Girder Movers
33 Undulator segments on individual girders (21 installed)
Undulator, Quad, BPM, BFW move with girder
Beam Finder Wire (BFW) retractable
Girder alignment with BFW at upstream and BBA at downstream end

16. First Beam to Main Dump 1st shot (stops in just into undulator)
BPMs mistimed
1st shot (stops in just into undulator)
2nd shot (all the way to dump)

17. 66 Beam Finder Wires (BFW) Tested and Aligned
…also emittance measured using 4 BFW’s
Centering Works Well

18. Undulator Re-Pointing is Tested
Enables motion of the entire undulator to steer electron beam and X-rays to a new axis

19. Undulator Cavity BPMs Calibrated with Beam
using girder motion vs. BPM reading
6% rms scale variation in X (will be improved)
fixed
6% rms scale variation in Y (will be improved)

20. Beam Based Alignment Schematic
BPM and quadrupole offsets are unknown
Vary energy, measure orbit to determine straight line
Δb0
Δb1
Δb2
Δb3
Δb0
Δq1
Δq2
Δq3 E2
x,x’ E1
Δy0
Δy1
Δy2
Δy3
Δy4
BPM Offsets Δbi
Quad Offsets Δqi
E1 < E2

21. Undulator Beam-Based Alignment Converged
Final Round of Beam-Based Alignment
Earth’s field pattern
100 µm
RMS = 64 µm
Verify alignment with quad strength variations
40 µm
RMS = 26 µm

22. Undulator Beam-Based Alignment Converged
20 mm
5 mm
Dispersion-Free (from 4.3 to 13.6 GeV)

23. Undulator Magnet Installed at U-25 (of 33)
Photo is just an example, and not U-25

24. High resolution RF-BPMs
RF-BPMs Resolve 10 nrad Kicks (~300 nm resolution)
20 BPMs in a 6-parameter fit (X0, X0', Y0, Y0', Xkick, Ykick) has a 0.5 µm Xrms fit residual and a 0.3 µm Yrms fit residual (NAVG=25).

25. Beam-Based Measured Field Integrals
MMF Measurements (U25)
Beam-based measurement agrees with MMF data
Beam-Based Measurements (U25)
IX1
IX1
IY1
IY1

26. Measured Undulator Girder Backlash (<1 mm)
3-parameter fit to 20 cavity BPMs along the undulator (y0, y0, and Dy)
Dy = 30 nrad kick due to quad
±4 mm
(y0, y0)
Feb. 7, 2009

27. Wakefield Energy-Loss in the LCLS Undulator
Wake field energy loss agrees well with theory
Important to adjust taper of undulator correctly

28. 84 meters of Undulator Installed

29. Observation of Undulator Radiation
Spontaneous X-Rays (U25 undulator only)
Radiation from dump bends
Used to measure X-ray energy at K-edge of YAG crystal absorption

30. X-Ray Diagnostics in the Front End Enclosure
Slit
Fixed
Mask
Solid
Attenuators
Reticule
K-Monochromator
Collimators
Thermal Sensor
Pop-in cameras
C0 collimator (in e- beam dump
Gas Attenuator
Gas
Detector
Beam Direction
Direct Imager
(Scintillator)
Pop-in cameras
Gas Detector
FEL Offset Mirror Systems

31. Summary Accelerator commissioned mostly to design goals
Laser heater commissioned and working well (does not salvage OTR screen quantitative use – many MPS problems)
Beam-based alignment converged to required level (should improve after undulators installed due to µ-shielding of Earth’s field)
New LTU wire scanners working routinely
Cavity BPMs commissioned and working fantastically
One undulator field integrals confirmed with beam
21 undulators installed
Full motion control on all girders (+ 21 undulators) working well
All beam finder wires (BFW) checked out and aligned with beam
BFW’s also used successfully to measure emittance
Full 6x6 feedback running (some over-sensitivity to machine setup still)
Soon hopefully to observe first FEL light

32. To Do
Tune up and run extended time (2 wks) at 4.3 GeV in preparation for AMO run
Streamline energy change for users and for rapid beam-based alignment
Install, set up, and verify new MPS system (controls)
Commission remaining undulators
Measure FEL gain
Commission FEE
Optimize FEL

33. LCLS Installation and Commissioning Time-Line
Install Undulators
First Light in FEH
LTU/Und Install
PPS Cert. LTU/Dump
FEE/NEH Install
First Light in FEE
X-Rays in NEH
FEH Hutch BO
CD-4 (7/31/2010)
PEP-II run ends
now J F M A M J J A A S O N D D J F M M A M J J A S O N D D J F M A M J J
Down
Down?
PPS
LTU/Und
Comm.
NEH Ops & Commissioning
Linac/BC2 Commissioning
Re-establish
e- to SL2
FEL/FEE
Commissioning
Nov. 3, 2008

34. Undulator Trajectory Jitter
Energy (GeV)
σx (μm)
σy (μm)
Beam size (μm)
13.64 9 7 33
9.25 12 6
4.3 18 23 36