P1258819240YajHE

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Physics Update P. Emma FAC Meeting October 27,
2005
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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
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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
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Electron Trajectory Jitter
Trajectory amplitude w.r.t. beam size
Total amplitude2 for N uncorrelated kicks, lt10
tolerance
sensitivity
Form budget with a few discreet tolerance levels,
opening challenging tolerances but holding tight
on more standard ones
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Trajectory Stability Sources of Jitter(f gt 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/sols current reg. (148 mags)
• Quad/solenoid mech. vibration (148 mags)
• CSR kicks with bunch length jitter (BC2, x only)
• Transverse wakes and charge jitter (X-band RF)
• Drive laser pointing stability

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Trajectory Stability Tols Expectations
System Stability Requirements at f gt 10 Hz

• Steering coils (30-100 ppM ? 6 of beam size)
• Trim coils (30-100 ppM ? 2)
• Misaligned quads (D ? 200 mm 25-100 ppM ? 6)
• Quad/solenoid vibration (0.05-1 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
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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)

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CSR-Induced x-Trajectory Jitter
?10 bunch length jitter ? ?16 core trajectory
jitter
1-nC
22 mm 20 mm 18 mm
core
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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 lt 10 Hz (120 Hz rate)
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Quad. Power Supply Regulation (Long-Term)
Dz lt 0.02 over all random quadrupole errors
Dk/k 1 to 0.01 rms over 24 hrs
Dk/k
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Magnet Polarities/Labeling Defined
MMF will measure magnets and clearly label
polarities
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Commissioning Tune-up Stoppers
Full set of beam diagnostics at each tune-up point
6 MeV
135 MeV
4.3 GeV
13.6 GeV
250 MeV
rf gun
L0
BC2
BC1
L3
L1
L2
X
linac
undulator
SLAC linac tunnel
research yard
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Commissioning Plans for each System
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LCLS Feedback Performance (use CSR ?P/P)
feedback off
J. Wu
at undulator entrance
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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)
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Relaxed Undulator Tolerances

• Full undulator error budget ? ?0.5C ? ?1F
  (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)

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Undulator Alignment Drift Long Term (24 hrs)
After beam-based alignment
?10 mm quad and BPM drift
MICADO steering applied
Tolerance set at ?5 mm alignment drift over 24 hrs
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Kems Correction Zones

• Zone 1 (non-invasive correction)
• 120-Hz traj-feedback (LTU BPMs)
• 0.1-Hz traj-feedback (und. BPMs)
• Zone 2 (Dt gt 1 hr, ?P/P0? gt 90, non-invasive)
• MICADO steering within undulator
• Zone 3 (Dt gt 24 hr, ?P/P0? gt 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 gt 1 wk, ?P/P0? lt 50, machine time)
• One iteration of BBA (lt1 hr)
• Zone 5 (Dt gt 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
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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
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Summary

• 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 !