Linac Coherent Light Source

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Linac Coherent Light Source Update
John N. Galayda LCLS Project Manager Basic
Energy Sciences Advisory Committee Meeting 2-3
August 2001
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• RD progress
• Gun
• Bunch compression
• Undulator
• X-ray optics
• FEL experiments
• Near-term RD goals
• Determine baseline gun performance
• Improve understanding of coherent synchrotron
  radiation effects
• Sub-Picosecond Photon Source (SPPS)

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• 1977-1990
• National Synchrotron Light Source, Brookhaven
  National Lab
• 1990-2001
• Advanced Photon Source,
• Argonne National Lab

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LINAC COHERENT LIGHT SOURCE
I-280
Sand Hill Rd
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Performance Characteristics of the LCLS
Peak and time averaged brightness of the LCLS and
other facilities operating or under construction
TESLA Performance
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Self-Amplified Spontaneous Emission
Electrons are bunched under the influence of the
light that they radiate. The bunch dimensions are
characteristic of the wavelength of the
light. Excerpted from the TESLA Technical Design
Report, released March 2001
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At entrance to the undulator
Exponential gain regime
Saturation(maximum bunching) Excerpted from the
TESLA Technical Design Report, released March 2001
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• RD progress Gun
• BNL Accelerator Test Facility
• Measurement of 0.8 mm-mrad emittance with 0.5 nC
  of charge
• Such high performance could make shorter LCLS
  pulses possible
• Details to be published in NIM-A, 2001 FEL
  Conference Proceedings

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• RD progress Gun
• SLAC gun test facility
• Comparison of computed and measured emittances
• Agreement is good for configurations tested thus
  far
• Facility upgrades planned to study configurations
  with lower emittance

ge, mm-mrad
LCLS Specification
Charge, picocoulombs
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Producing short bunches At low energy, space
charge repulsion degrades the beam
properties Accelerate the bunch, then compress
it.
7 MeV ?z ? 0.83 mm ?? ? 0.2
150 MeV ?z ? 0.83 mm ?? ? 0.10
250 MeV ?z ? 0.19 mm ?? ? 1.8
4.54 GeV ?z ? 0.022 mm ?? ? 0.76
14.35 GeV ?z ? 0.022 mm ?? ? 0.02
Linac-X L?0.6 m ?rf180?
RF gun
Linac-1 L?9 m ?rf ?-38
Linac-2 L?330 m ?rf ?-43
Linac-3 L?550 m ?rf ?-10
new
Linac-0 L?6 m
undulator L?120 m
25-1a 30-8c
21-1b 21-1d
21-3b 24-6d
X
...existing linac
BC-1 L?6 m R56 ?-36 mm
BC-2 L?24 m R56 ?-22 mm
DL-1 L?12 m R56 ?0
DL-2 L?66 m R56 0
SLAC linac tunnel
undulator hall
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DE/E
DE/E
DE/E
Under-compression
Over-compression
2sz0
z
z
z
2sz
V V0sin(wt)
Dz R56DE/E
RF Accelerating Voltage
Path Length-Energy Dependent Beamline
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Coherent Synchrotron Radiation (CSR)
sz
Coherent radiation for lr gtgt sz
lr
A
AB
B
R
e
? ltlt1
...from Derbenev, et. al.
Free space radiation from bunch tail at point A
overtakes bunch head, a distance s ahead of the
source, at the point B which satisfies... s
arc(AB) AB R? 2Rsin(?/2) ? R? 3/24 and
for s sz (rms bunch length) the overtaking
distance is... L0 ? AB ? (24szR2)1/3, (
LCLS L0 1 m)
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CSR Effects ? Bunch Energy Gradient
Charge distribution
sz
TAIL
DE/E
HEAD
(mean loss)
CSR wakefield
z
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CSR Effects ? Emittance Growth
Energy loss in bends causes transverse position
spread after bends ? x-emittance growth
Radiation in bends
s
DE/E 0
DE/E lt 0
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• RD Progress Coherent Synchrotron Radiation
• CSR sets a lower limit on LCLS as a laser
• LCLS could produce 50 fsec pulses of spontaneous
  radiation
• New ANL model fits latest data is the model
  accurate?
• LCLS bunch compression can be retuned to
  accommodate

energy spread
rms bunch length ps
emittance mm-mrad
Q ? 0.3 nC
M. Borland, PRST-AB v.4, 074201(2001) Borland,
Braun, Doebert, Groening, Kabel, CERN/PS
2001-027(AE)
Courtesy M. Borland, J. Lewellen, ANL
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• RD Progress Prototype Undulator
• Titanium strongback mounted in eccentric cam
  movers
• Magnet material 100 delivered
• Poles gt90 delivered
• Assembly underway

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Helmholtz Coil magnet block measurement
Translation stages for undulator
segment
Poletip alignment fixture
Magnet block
clamping fixtures
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Planned beam diagnostics in undulator include
pop-in C(111) screen To extract and observe x-ray
beam, and its superposition on e-beam
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• RD Progress Undulator diagnostics
• P. Krejcik, W. K. Lee, E. Gluskin
• Exposure of diamond wafer to electron beam in
  FFTB-
• Same electric fields as in LCLS
• No mechanical damage to diamond
• Tests of crystal structure planned

Before
After
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• RD Progress X-ray optics
• LLNL tests of damage to silicon crystal
• Exposure to high- power laser with similar energy
  deposition
• Threshold for melting 0.16 J/cm2, as predicted in
  model
• Fabrication/test of refractive Fresnel lens
• Made of aluminum instead of carbon
• Machined with a diamond point
• Measurements from SPEAR presently under analysis

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Warm Dense Matter Experiment
250 mm aperture
Back-scatter x-ray spectrometer
Incident Beam Monitors
Laser
FEL Beam
Spectrometer
100 mm thick sample
Outgoing Beam Monitor
Focusing Optic
50-100 mm aperture
Imaging detector
Variable beam attenuator
Sample Tank
PPS beam stops
Optics Tank
WDM Shielded Room
13 m
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• RD Progress FEL physics
• More complete analysis of HGHG
• A. Doyuran, et al. PRL vol. 86, Issue 26, pp.
  5902-5905, June 25, 2001
• LEUTL experiments ongoing
• Milton, et al. Science vol. 292, Issue 5524,
  2037-2041, June 15, 2001
• VISA experiment saturation
• To be published in proceedings of 2001 FEL
  conference

Data from BNL/ANL High-Gain Harmonic Generation(HG
HG) Experiment
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LEUTL Gain Curve _at_ 530 nm on March 10, 2001
107
106
105
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Radiated Energy (a.u.)
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October,2000
102
101
100
10
25
5
15
20
0
Distance Traversed in Undulator (m)
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16 March 2001
Visible to Infrared SASE Amplifier
BNL-LLNL-SLAC-UCLA
VISA Pulse Energy vs. Position
Wavelength 830 nm
Onset of Saturation
Data Points taken along VISA Undulator
Wavelength 830nm RMS Bunch Length 900
fs Average Charge 170 pC Peak Current 200
A Measured Projected Emittance 1.7 mm
mrad Energy Spread 710-4 Gain Length 18.5
cm Equivalent Spontaneous Energy 5 pJ Peak SASE
Energy 10 mJ Total Gain 2106
Enclosure for 4-m long VISA undulator
Pop-In Diagnostics
Direction of Electron Beam
Preliminary recent results (unpublished) from
VISA showing large gain (2 106) in SASE FEL
radiation and evidence of saturation at 830 nm.
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• Near-term RD goals
• Gun RD
• Thorough investigation of gun operation at LCLS
  parameters
• Laser upgrade
• Linac energy upgrade
• Experiment/model comparison at 1 mm-mrad
  emittance, 0.5-1 nC
• Bunch compression, coherent synchrotron radiation
• Install a bunch compressor in the SLAC linac
• Continue start-to-end modeling

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• Bunch compression studies with SLAC linac in 2003
• Compatible with PEP-II injection
• Capable of producing 80 fsec electron bunches
• Goal first studies in 1/2003, 1 year of tests
• pump/probe techniques
• Accelerator physics opportunities to study wake
  fields
• Of great importance to LCLS
• Short bunches are ideal for advanced accelerator
  RD Strong SLAC support

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LCLS X-ray Laser Physics
The sixth experiment Produce lt 230 fsec
pulses of SASE radiation

• LCLS will be used to explore means of producing
  ultra short bunches (lt 50 fs). Alternative
  techniques will be investigated
• Stronger compression of the electron bunch
• No new hardware is required
• Photon bunch compression or slicing
• Principle spread the electron and photon pulses
  in energy recombine optically or select a slice
  in frequency

• Seeding the FEL with a slice of the photon pulse
• Principle select slice in frequency, then use it
  to seed the FEL

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Two-Stage Chirped-Beam SASE-FEL for High Power
Femtosecond X-Ray Pulse Generation
C. Schroeder, J. Arthur, P. Emma, S. Reiche,
and C. Pellegrini Stanford Linear Accelerator
Center UCLA Strong possibility for
shorter-pulse operation
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Two-stage undulator for shorter pulse
Mitigates e- energy jitter and undulator wakes
Also a DESY scheme which emphasizes line-width
reduction (B. Faatz)
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• LCLS Construction
• FY2003 6M for project engineering and design,
  3M for RD
• Prepare bid packages
• FY2004 Start of Construction
• Injector construction and installation
• Bunch compressor construction
• Start construction of near hall
• Undulator procurement
• FY2005
• Injector commissioning
• Bunch compressor installation
• Start construction of far hall
• Undulator, experiment construction
• FY2006 Installation
• Linac commissioning
• Undulator and experiment installation
• LCLS commissioning

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LCLS research activities span the full range of
challenges to be met in creating and exploiting
an x-ray laser SLAC has supplemented its
extraordinary capabilities with the expertise and
resources at partner labs to make LCLS
possible LCLS can be a reality by 2007
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End of Presentation