1. Physics Update
P. Emma
FAC Meeting October 27, 2005
LCLS

2. No New Physics Surprises
1999: Surface roughness wakefield
2001: CSR micro-bunching instability
2002: Space-charge enhanced micro- bunching instability
2004: AC resistive-wall undulator wake
2005: no new set-backs?
We must be too busy with construction?
Thanks for past help from:
K. Bane, Z. Huang, G. Stupakov, and Saldin, Schneidmiller, Yurkov

3. Normal Incidence Laser on Cathode
Advantages
No lossy, pulse distorting grating
Non-dispersed beam – less $
Mirror change without gun vent
Optics allows continuous variation of cathode beam size
Disadvantages
Mirror wakefield (solved)
Mirror requires space (solved)
e- beam
laser beam
previous grazing incidence
Dowell, Gilevich, Limborg, White

4. Electron Trajectory Jitter
Trajectory amplitude w.r.t. beam size
Total amplitude2 for N uncorrelated kicks, <10%
tolerance
sensitivity
Form budget with a few discreet tolerance levels, opening challenging tolerances but holding tight on more standard ones

5. Trajectory Stability – Sources of Jitter (f > 10 Hz)
Expected Sources of Transverse Jitter
Steering coil current regulation (120 x, 121 y)
Bend magnet trim coil current reg. (13 x & 2 y)
Misaligned quads/sol’s + current reg. (148 mag’s)
Quad/solenoid mech. vibration (148 mag’s)
CSR kicks with bunch length jitter (BC2, x only)
Transverse wakes and charge jitter (X-band RF)
Drive laser pointing stability

6. Trajectory Stability – Tol’s & Expectations
System Stability Requirements at f > 10 Hz
Steering coils ( ppM  6% of beam size)
Trim coils ( ppM  2%)
Misaligned quads (D  200 mm: ppM  6%)
Quad/solenoid vibration ( mm required  10%)
CSR kicks (1 nC, Dsz/sz  10%:  ~20%, x-only)
Wakes (D  200 mm, DN/N  2%  2%)
Drive laser pointing ( ~1%)
0.2 nC is more stable

7. Quadrupole Magnet Vibration
Existing Linac ‘QE’ Quadrupole Magnets
R. Stege,
J. Turner, 1994
rubber boot on water pump
12 quads need rms 500 nm (most new injector quads)
101 magnets need rms 100 nm (existing linac quads)
35 quads need rms 50 nm (mostly new LTU quads)

8. CSR-Induced x-Trajectory Jitter
10% bunch length jitter 
16% ‘core’ trajectory jitter
1-nC
22 mm
20 mm
18 mm
core

9. Trajectory Feedback at Undulator Start
undulator starts at Z = 0
5-mm BPM resolution of final 10 BPMs gives centroid stabilization to 5% of rms beam size at: f < 10 Hz (120 Hz rate)

10. Quad. Power Supply Regulation (Long-Term)
Dz < 0.02 over all random quadrupole errors
|Dk/k| = 1% to 0.01% rms over 24 hrs+
|Dk/k|

11. Magnet Polarities/Labeling Defined
MMF will measure magnets and clearly label polarities

12. Commissioning – Tune-up ‘Stoppers’
Full set of beam diagnostics at each tune-up point
6 MeV
Jan. through July ’07
135 MeV
250 MeV
4.3 GeV
13.6 GeV rf
gun L0
TCAV0
TCAV3 e
BC1
BC2
…linac L1 X L2 L3
undulator
abort
SLAC linac tunnel
research yard

13. Commissioning Plans for each System

14. LCLS Feedback Performance (use CSR P/P)
feedback off
DIpk/Ipk0 (%)
feedback on
J. Wu
at undulator entrance

15. CSR as Relative Bunch Length Monitor
Red curve: Gaussian
Black curve: Uniform
Red dots: ‘Real’
J. Wu
CSR detector is critical to LCLS stability (UCLA)

16. Relaxed Undulator Tolerances
Full undulator error budget  0.5°C  1°F (H.-D. Nuhn)
Beam-Finder Wire (BFW) to locate upstream end (D. Walters)
Alignment drift tolerances loosened
Correction strategy with target time-scales (FAC suggestion)

17. Undulator Alignment Drift – Long Term (24 hrs)
10 mm quad and BPM drift
After beam-based alignment
MICADO steering applied
Tolerance set at 5 mm alignment drift over 24 hrs

18. Kem’s Correction Zones*
Zone 1 (non-invasive correction)
120-Hz traj-feedback (LTU BPM’s)
0.1-Hz traj-feedback (und. BPM’s)
Zone 2 (Dt > 1 hr, P/P0 > 90%, non-invasive)
MICADO steering within undulator
Zone 3 (Dt > 24 hr, P/P0 > 75%, invasive)
Weighted steering of undulator traj. (1 min.)
... or quadrupole gradient scans - fast BBA (10 min.)
Possible x-ray pointing (few min.)
Zone 4 (Dt > 1 wk, P/P0 < 50%, machine time)
One iteration of BBA (<1 hr)
Zone 5 (Dt > 6 mo, shut-down)
Tunnel survey with all movers set to zero (1 wk)
Full 3 iterations of BBA (~3 hrs)
* FAC suggestion, April ‘05

19. 1-Å with Optical Klystron Enhancement
Future?
K = 2.7
E = 13.6 GeV
ge = 1.2 mm
Ipk = 3.4 kA
b = 30 m
sE/E = 0.005%
Laser-Heater  1/2
-bunching issue?
Shim gap  Dg = 2 mm
SASE sim. ~longer Lsat
4 “OK” chicanes
(long breaks)
Yuantao Ding, Zhirong Huang

20. Summary Electron beam commissioning through BC1 starts Dec. ’06 !
Normal incidence simplifies drive laser (Gilevich)
Trajectory stability expectations: 24% x & 14% y
Quadrupole current regulation specified
Magnet polarities defined
Commissioning plans formed
Feedback systems require CSR monitor (UCLA)
Relaxed undulator tolerances (Milton, Nuhn)
1-Å future operation with “OK”?
Electron beam commissioning through BC1 starts Dec. ’06 !