LCLS Beam and Detector Simulations

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LCLS Beam and Detector Simulations

• ICFA Mini-Workshop on Commissioning of X-FELs
• April 18-22, 2005

This work was performed under the auspices of
the U.S. Department of Energy by the University
of California, Lawrence Livermore National
Laboratory under contract No. W-7405-Eng-48 and
by Stanford University, Stanford Linear
Accelerator Center under contract No.
DE-AC03-76SF00515 for the LCLS project..
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Outline

• Spontaneous Radiation Model
• Spontaneous and FEL signals in Direct and
  Indirect Imager Diagnostics
• Spontaneous Reflection in Undulator Vacuum
  Chamber
• Conclusions

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Spontaneous Radiation Model
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Spontaneous Data Chain

• UCLA Near-Field Calculator
• 2 Gbyte HDF5
• HDF5 to Paradox Converter
• (x,y,E,P) Paradox format, 4 X 1 GByte
• ReBinner Coarser Energy Bins (159)
• (x,y,E,P) Paradox format, 350 MByte
• DB Converter faster to read
• (E,Px,y) Paradox, 50 MBytes
• Viewer

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Spontaneous Fluence at NEH Hutch 1
Te 4.5 GeV Z 243 m Dx 1.0 mm Dy 0.3
mm 1.85 mJ
Te 14.5 GeV Z 243 m Dx 0.3 mm Dy 0.1
mm 18.2 mJ
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4
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Energy Slices
Near-Field calculation 88 m from
End-of-Undulator, Sven Richie, UCLA
20 mm
20 mm
Far-Field calculation 400 m from
Center-of-Undulator, Roman Tatchyn, SSRL
0 lt E lt 10 keV
7.6 lt E lt 9.0 keV
10 lt E lt 20 keV
20 lt E lt 27 keV
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LCLS beam footprint
Expected LCLS beam profile contains FEL and
Spontaneous halo
2-3 mJ FEL
20 mJ Spontaneous
3 mJ High energy core Eg gt 400 keV
At entrance to NEH, FEL tuned to 8261 eV
Fundamental
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Spontaneous and FEL signals in the Direct Imager
Diagnostic
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Camera Image Calculator Chain
Spontaneous DB
Photoelectrons in Camera (2.5 x Zeiss SITEC
CCD)
Spontaneous e x FEL
Absorbed in 25 mm LSO
(E,Px,y)
x e
FEL
Transmitted by Material
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14.5 GeV Spontaneous, NEH H1
All photons
Stops in 25 mm LSO
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14.5 GeV Spontaneous Direct Imager Signal
Photons
Energy
All photons
Stops in 25 mm LSO
Photoelectrons/Pixel
CCD photoelectron levels lt 150K e-
Full well (16 bit) 327K e- so this is ½ scale on
CCD readout
(X-Ray resolution 300 x 100 mm)
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14.5 GeV Spontaneous FEL
Photons
Energy
All photons
Stops in 25 mm LSO
Need attenuation of 2.4 x 10-4 for CCD full well
Photoelectrons/Pixel
(X-Ray resolution 300 x 100 mm)
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Use of 16.9 mm B4C Attenuator
Raw photon spectra of FEL Spontaneous
Spectra of FEL Spontaneous after B4C
Photons/keV
Spectra of photons stopping in LSO
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Direct Imager Image
14.5 GeV
100 FEL Spontaneous through 16.8 mm B4C into
25 mm LSO
Good FEL signal at ½ CCD Full Scale but increased
background in image
(X-Ray resolution 300 x 100 mm)
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How faint can FEL be?
(X-Ray resolution 300 x 100 mm)
14.5 GeV
1 FEL Spontaneous directly into 25 mm LSO
0.01 FEL Spontaneous into 25 mm LSO
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4.5 GeV Spontaneous, NEH H1
All photons
1.852 mJ
Direct Imager Photoelectrons
8 x 1011
Photons / keV
0
Stops in 25 mm LSO 1.205 mJ
Direct Imager Photoelectrons
(X-Ray resolution 1000 x 300 mm)
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Total Energy Calorimeter Concept
Cooler
CMR Sensor
Sapphire heat sink
CMR W vs T
Si or Be 1x1x.5 mm
Xray Beam
Electrothermal Feedback
Apply constant V Measure I Calculate P
Direction of heat flow
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Energy deposition in each layer
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SINDA Cool Down Time Results
Cool Down Time is about 0.6 ms
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Response to 14.5 GeV Spontaneous
Energy Absorbed in 500um Silicon
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Response to 14.5 GeV Spontaneous 0.01 FEL
Energy Absorbed in 500um Silicon
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Spontaneous Monte Carlo Chain

• Spontaneous DB
• (E,Px,y) Paradox, 50 Mbytes
• Inject FEL
• (E,Px,y) Paradox, 50 Mbytes
• Cumulative DB
• (x,y,FE) Paradox, 50 Mbytes
• Photon MC Generator creates random photons
  according to cumulative distribution
• (x,y,z,vx,vy,vz,E) of individual photons

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Spontaneous Monte Carlo Simulation
Photon starting angles generated to give
calculated spontaneous spatial distribution
Photon starting x, y matches electron
distribution, a Gaussian with s 30 mm
Photon starting z is uniform along undulator
(from 0 lt z lt 130 m)
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Each photon final x, y has its own cumulative
energy distribution
Calculated far-field energy spectrum
Monte Carlo Energy Distribution
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Simulated spatial distributions agree with
far-field calculation
All Photons
Monte Carlo 465 m from beginning of undulator
Far-Field Calculation 400 m from center of
undulator
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Simulated spatial distributions agree with
far-field calculation higher orders
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Monte Carlo Simulation of LCLS
100 FEL Spontaneous
1 FEL Spontaneous
0.1 FEL Spontaneous
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Indirect Imager Simulation
1 m
2.90068 degrees
Spontaneous e FEL
101 mm
Be/SiC 300 layer pairs 60 Angstrom period Gamma
0.2 On 0.5 mm thick Si 10 cm diameter
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For Full Power FEL ML allows imager to operate
w/o damage
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0.1 FEL
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Low Energy Background Dominates
Egt2.5 keV Cleans up signal !
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Spontaneous Emission Angle Below Critical Angle
243 m
130 m
60-200 mm
Qmax 0.5 1.8 mRad
Qmin 0.2 0.8 mRad
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Vacuum Pipe Simulation 14.5 GeV
With pipe
Without pipe
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Line outs through center
With pipe
Without pipe
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Reflection at higher orders
UCLA Calculation, without pipe
Monte Carlo, without pipe
Monte Carlo, with pipe
0 lt E lt 10 keV
10 lt E lt 20 keV
20 lt E lt 30 keV
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Photon Energies gt 400 KeV
Without pipe
With pipe
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Reflection in pipe at 4.5 GeV
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Tilted pipe at 14.5 GeV
Pipe parallel to beam
Pipe tilted 19 mR, raised 0.9 mm, and shifted to
the right 0.9 mm
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Summary

• Beam modeling codes include direct calculations
  of near-field spontaneous FEL signals and
  Monte-Carlo simulations of scattering
• Reflection off of undulator vacuum chamber
  seriously distorts the spontaneous radiation
  pattern
• Direct imager model in progress to specify
  scintillator and attenuator thickness, and CCD
  gain parameters. Similar model for Indirect
  Imager, and Calorimeter.
• Modeling of other diagnostics is proceeding in
  FY05