1. Linac Physics, Diagnostics, and Commissioning Strategy P
Linac Physics, Diagnostics, and Commissioning Strategy P. Emma LCLS DOE Review August 12, 2004
LCLS
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

2. 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 %
135 MeV
z  0.83 mm
  0.10 %
250 MeV
z  0.19 mm
  1.6 %
4.54 GeV
z  mm
  0.71 %
14.1 GeV
z  mm
  0.01 %
Linac-X
L =0.6 m
rf= -160 rf
gun
new
Linac-1
L 9 m
rf  -25°
Linac-2
L 330 m
rf  -41°
Linac-3
L 550 m
rf  -10°
Linac-0
L =6 m
...existing linac
21-1b
21-1d X
21-3b
24-6d
25-1a
30-8c
undulator
L =130 m
BC-1
L 6 m
R56 -39 mm
BC-2
L 22 m
R56 -25 mm
DL-1
L 12 m
R56 0
LTU
L =275 m
R56  0
SLAC linac tunnel
research yard
(RF phase: frf = 0 is at accelerating crest)
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

3. Complete & Detailed Design (cathode to dump)
BC2 L3
LTU
cathode
undulator
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

4. after BC1 after X-RF after L1 after DL1 after BC2 after L3 at und.
(2002 example)
after BC1
after X-RF
after L1
after DL1
after BC2
after L3
at und.
after L2
energy profile
phase space
time profile
sz = 830 mm
sz = 190 mm
sz = 830 mm
sz = 23 mm
sz = 830 mm
sz = 23 mm
sz = 190 mm
sz = 23 mm
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

5. Location of Main Linac Diagnostics
5+ energy spread meas. stations (optimized with small b)
5+ emittance meas. stations designed into optics (Dyx,y)
BPMs at or near most quadrupoles and in each bend syst.
RF deflectors for slice e and sE measurements (L0 & L3) rf
gun
T-cav.
gex,y
T-cav. L0
gex,y
gex,y
gex,y
gex,y
...existing linac L1 X L2 L3 sE sE sE
E
E
E sE sE
E
E
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

6. Linac ‘Commissioning’ (Physics)
How to setup Ipk = 3.4 kA, ge  1.2 mm, etc.
What to measure and what to adjust
Longitudinal phase space
Bunch Length
Energy Spread (proj. & slice)
Transverse phase space
Projected Emittance
Slice Emittance
Feedback Systems
Will show a few examples
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

7. Setup of Linac-0 RF minimize energy spread with L0 RF phase
sy = bunch length
Approximate injector parameters needed prior to linac commissioning.
RF-deflector at 1 MV
minimize energy spread with L0 RF phase
RF-deflector
Phasing L0-Linac
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

8. (X-band off, BC1 bends at 295 MeV)
Setup of Linac-1 RF
20-mm res. BC1 BPM
20-mm res. BC1 BPM
LX RF phase
L1 RF phase
Linac-1 RF phase scan
(X-band off, BC1 bends at 295 MeV)
Linac-X RF phase scan
(BC1 bends at 250 MeV)
set phase to -25˚0.5˚
set phase to -160˚0.5˚
Linac-1
new rf
gun
21-1b
21-1d X
Turn on BC1 energy feedback
Switch off BC2 chicane
Use sec-25 RF-deflector to meas. bunch length (sz1)
Adjust S-band RF phase (0.5˚) to set sz1  195 10 mm
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

9. Verify BC1 Setup
(NO CSR)
Scan Linac-1 S-band RF phase and use BC2 BPM to find maximum wake-induced energy loss across Linac-2 rf
gun L1 X L2
well tested at SPPS
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

10. (BC2 bends at 5.3 GeV, 2 klys. off)
Setup of Linac-2 RF
40-mm res. BC2 BPM
5-mm res. LTU BPM
(NO CSR)
L2 RF phase
L2 phase
Linac-2 RF phase scan
(BC2 bends at 5.3 GeV, 2 klys. off)
Scan Linac-2 phase & use LTU BPM to find max. wake-induced energy loss across Linac-3
set phase to -41˚0.5˚
Turn on BC2 energy feedback
Use sec-25 RF-deflector to measure length (sz2)
Adjust L2 RF phase (0.5˚) to set sz2  20  2 mm
Linac-3 phasing is trivial (5˚) L2 L3
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

11. Emittance Meas. Simulation in LCLS
Multiple OTR screens
Multiple wire-scanners
Quad-scans on single OTR
Quad-scans on OTR with RF-deflector
OTR1,2,3
WS11,12,13
BC1
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

12. 135-MeV x-profiles (from tracking)
sx  118 mm
sx  49 mm
sx  120 mm
non-Gaussian
gex = 0.75 ± 0.04 mm
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

13. Slice-Emittance Measurement Simulation
sy  bunch length
RF-deflector at 1 MV
slice OTR 10 times
135 MeV
quad scanned
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

14. Slice-Emittance Measurement Simulation
(slice-y-emittance also simulated in BC1-center)
Injector (135 MeV) with S-band RF-deflector at 1 MV
= meas. sim.
= calc.
= y distribution
= actual
(same SLAC slice-e code used at BNL/SDL)
DL1 slice-emit on WS02
slice-5
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

15. Empirical BC1/BC2 Dispersion Correction
actual data from SPPS chicane
Dx  /2
Residual x-dispersion (and its angle) is precision minimized using ‘tweaker’ quads in the chicane
SPPS chicane with quads
Correct h and (ah + bh), orthogonally with 2 quads
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

16. Linac-To-Undulator (LTU)
vertical bends
energy centroid & spread meas. (OTR) (310-5 & 10-4) + collimation
4 e-wires, collimators, 1 OTR
vertical bend 4.7 mr
horizontal jog 1.25 m
energy diagnostics
emit. diagnostics
bunch length diag.
collimators
CSR cancellation
branch points for future undulators
spontaneous undulator possible
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

17. Slice-Emittance Configuration for LTU
nominal optics
(proj. emit.)
WS31-34
undulator…
slice-emit.
meas. optics
stopper
inserted
OTR33
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

18. Slice-Emittance Measurements in LTU
LTU at 14 GeV with S-band RF-deflector at 24 MV x z x
= meas. sim.
= calc.
= y distribution
= actual y
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

19. Slice Energy Spread Measurements in LTU
LTU at 14 GeV with S-band RF-deflector at 24 MV
sE/E  10-4
DE/E0 z
sx  12 mm x
FEL goal y
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

20. LCLS Longitudinal Feedback Simulation
Feedback OFF
Feedback ON
Juhao Wu (SLAC)
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004

21. Summary LCLS linac is operationally flexible
Diagnostics have been incorporated into optical design and simulated (1st pass)
Two RF-deflectors allow time-resolved measurements at low and high energy
Tune-up algorithms have been considered, but more work is needed
Feedback system simulations show energy, peak current, and timing are stabilized
Work continues
P. Emma, SLAC
LCLS DOE Review – Aug. 12, 2004