Issues and R

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Issues and RD Critical to the LCLS
Paul Emma SLAC
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Linac Coherent Light Source (LCLS)
4th-Generation X-ray SASE FEL Based on SLAC Linac
3
Other FEL-based sources being tested, built, or
planned

• Source Development Laboratory (SDL) at BNL-NSLS
• Electron beam testing

• VISA experiment at BNL-ATF
• Saturation achieved, March 2001

• FELs under study in Japan, Italy, England and
  Germany (BESSY II)

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LCLS Project Update

• Design Study Report published 1998 (SLAC-R-521)
  led by Max Cornacchia

• New LCLS project leader at SLAC is John Galayda
  (formerly of ANL/APS)

• Critical Decision-0 (CD-0) approval was signed by
  DOE in June 2001

• Published plan for first 5 experiments
  (femto-chemistry, atomic physics, warm dense
  matter, ), Sep. 2000

• Pre-engineering in 2003, construction in 2004,
  and operation in 2007

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LCLS Issues and RD
? Injector Requirements
? Acceleration and Compression
? Undulator
? X-ray optics
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RF Photo-Cathode 1.6-cell S-band Gun
Designed by D. Palmer (SLAC) R. Miller J.N.
Weaver X.-J. Wang (BNL) I. Ben-Zvi, K.
Batchelor C. Pellegrini (UCLA) J.
Rosenzweig K.-J. Kim (ANL)
Booster linac 150 MeV Emittance 1
mm Charge 1 nC Current
100 A
full cell
half cell
Courtesy of J. Clendenin, M. Hernandez, J.
Schmerge, SLAC
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Gun Test Facility
(GTF) in SSRL Injector Vault
LCLS Injector RD
diagnostic room
Courtesy of J. Schmerge, SLAC
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GTF Emittance Measurements Spring 2001
LCLS requires 10 ps FWHM Q 1 nC ge 1 mm
Emittance measured at 30 MeV with quad-scan on
YAG screen, varying charge and bunch length
more work ahead
no temporal pulse shaping yet
Quad-scans on YAG screen, no space charge
correction
S. Gierman, J. Schmerge, SLAC
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LCLS Acceleration and Compression
RF gun
undulator

• Emittance control given coherent synchrotron
  radiation in bends
• Adequate machine stability (RF, charge,
  bunch-timing, )

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X-band compensation
S-band RF curvature and T566 non-linearity
sz 840 mm
? 20 MV, 0.6 m long
linearizer also reduces bunch length sensitivity
to timing jitter
Similar scheme used at TESLA DESY (P. Piot, et.
al.)
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0.5-Meter X-Band RF Accelerating Structure
And Linearizer allows analytical modeling of
wakes (uniform pulses) and therefore fast,
automated LCLS parameter optimization
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TRACKING
Elegant, by M. Borland
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Start-to-End Simulations
Time-sliced beam is input to Genesis-1.3,
including centroid and rms of each slice in 6D
CSR model is critical
M. Borland, WPPH103
S. Reiche, WPPH119
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Stability Studies
Pulse-to-pulse jitter estimates based on
repeated tracking including parameter variations
Track 100k macro-particles in long.-2D 2000 times
with jitter
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LEUTL CSR Measurements (ANL)
energy spread
rms bunch length ps
At end of LEUTL bunch compressor chicane
Using line-charge CSR model of Saldin, et. al.
emittance mm-mrad
Q ? 0.3 nC
RF phase deg-S
M. Borland, RPAH001
? over-compression
Courtesy M. Borland, J. Lewellen, ANL
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Transverse RF Deflector for Bunch Length
Measurement
P. Emma, J. Frisch, P. Krejcik, G. Loew, X.-J.
Wang
S-band
V0 ? 15 MV sz ? 22 mm, E ? 6 GeV
P. Krejcik, WPAH116
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Undulator Hall (FFTB)
Install 122-m long planar undulator in existing
FFTB hall
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Undulator (ANL/APS)
1-mm BPM ? cavity and button-type in compact
package (G. Decker, ANL)
Quad-magnets and undulator sections on
independent movers
E. Moog, TOPA012
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LCLS 9-Pole Prototype Undulator (ANL)
3.4-m section is under construction at ANL
E. Moog, TOPA012
Courtesy E. Gluskin, ANL
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Undulator Beam-Based Alignment
sx gt 500 mm
sx ? 1.5 mm Dj ? 100
Simulate alignment procedure with many realistic
errors BPMs, quads, poles,
RON simulation shows saturation length increase
by lt1-gain length (R. Dejus, N. Vinokurov)
BBA used at TTF-FEL DESY (P. Castro, et. al.)
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Wakefields in Undulator
long aspect ratio of surface roughness is
important
S. Reiche, WPPH119
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X-ray Optics RD

• Intense x-ray interaction with matter

• Attenuation cell (1?10-4)

• Experimental station needs

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Motivation for even shorter x-ray pulses
Coulomb Explosion of Lysozyme (50 fs)
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Two-stage undulator for shorter pulse
C. Schroeder, WPPH121
Mitigates e- energy jitter and undulator wakes
Also a DESY scheme which emphasizes line-width
reduction (B. Faatz)
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VISA
Visible to Infrared SASE Amplifier
LCLS Collaboration
BNL-LLNL-SLAC-UCLA
4-m undulator in ATF at BNL for SASE RD at 830 nm
Wavelength 840nm Average Charge 170 pC Measured
Projected Emittance 1.7 mm Energy Spread 0.07
Gain Length 18.7 cm Total Gain 2107
Preliminary results (unpublished) showing large
gain (2?107) in SASE FEL radiation and evidence
of saturation at 840 nm.
A. Tremaine, WPPH122
A. Murokh, WPPH118
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Short Bunch Generation in the SLAC Linac
Damping Ring (ge ? 30 mm)
Compress to 80 fsec in 3 stages

• New proposal for
• LCLS accelerator and x-ray optics RD
• Ultra-short x-ray science program at SLAC

1.5
Add to understanding of CSR and X-ray optics
P. Emma, FPAH165
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Summary of Key Issues

• Emittance generation and preservation

• Gun ge ? 1 mm, repeatable at 120 Hz

• Need better understanding of CSR

• Stable operation

• RF, laser, and feedback systems

• Undulator errors and trajectory control

• Fabrication, alignment, and BPMs

• Wakefields

• SASE saturation at 1Å