The echo-enabled harmonic generation (EEHG) options for FLASH II

1
The echo-enabled harmonic generation (EEHG)
options for FLASH II
Free Electron Laser Beam Dynamics Meeting

• Haixiao Deng, Winfried Decking, Bart Faatz
• FEL division, Shanghai Institute of Applied
  Physics (SINAP)
• Hasylab, Deutsches Elektronen-Synchrotron (DESY)
• DESY, Hamburg, Dec 06, 2010
• denghaixiao_at_sinap.ac.cn

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Contents

• Introduction
• EEHG options for FLASH II
• Numerical modeling
• Beam energy chirp CSR effects
• FEL properties Discussions
• Summary Outlook
• Acknowledgments

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Introduction
Echo-enabled harmonic generation (EEHG)
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Why EEHG ?
G. Stupakov, EEHG for seeded FEL-theory and
experiment, KEK, Nov, 2010
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Current status of EEHG

• Works in the theoretical frame
• G. Stupakov., PRL, 102, 074801 (2009)
• D. Xiang et al., PR-ST AB, 12, 030702 (2009)
• D. Xiang et al., PR-ST AB, 12, 080701 (2009)
• Z. Huang et al., FEL09, MOPC45
• D. Xiang et al., PR-ST AB, 12, 060701 (2009)
• G. Pen et al., NIMA, 612, 254 (2010)
• J. Yan et al., NIMA, 621, 97 (2010)
• Experimental demonstration of the EEHG signal at
  SDUV-FEL NLCTA, independently.
• Z. T. Zhao et al., IPAC10, FEL10
• D. Xiang et al., PRL, 105, 114801 (2010)
• FERMI, Swiss-FEL, FLASH II, LCLS II/III etc.

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EEHG options for FLASH II
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EEHG options for FLASH II
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EEHG optimization for FLASH II
EEHG theory
EEHG simulation steady-state
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Main parameters
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The ideal projected bunching
60th harmonic
20th harmonic
40th harmonic
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Numerical modeling
Macro-particles generator (GENESIS ASTRA )
3D laser-beam interaction in Modulator1 (MATLAB
program)
Particle tracking in Chicane1 (ELEGANT CSRtrack)
3D laser-beam interaction in Modulator2 Chicane
2 (MATLAB program)
Self-consistent FEL simulation in the main
radiator (GENESIS)
The dynamics of Chicane 2 (small R56) is just
linear optics
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Numerical modeling
All procedures are controlled by MATLAB scripts
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Laser-beam interaction algorithm

• No FEL equation induced, capable for fs seed
  laser
• Beam dynamics under field maps (Electric
  magnetic)
• Radiations from the electron beam are ignored

Detuning of LCLS laser-heater
CEP effects of a fs laser
Haixiao Deng et al, Chinese Physics C, 2011, in
press
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Self-consistent FEL simulation

• The problem in the conventional s2e simulation
• Self-consistent s2e FEL simulation
• SASE start-up, fluctuation and noise propagation
• 1pC, single-spike mode for SXFEL, 6M
  macro-particles

Jun Yan, Meng Zhang and Haixiao Deng, NIMA 615,
249 (2010)
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Beam energy chirp CSR effects
Flash 1nC s2e results
Z. Huang et al., FEL09, MOPC45
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Energy chirp effects
20th harmonic
60th harmonic
40th harmonic
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The CSR-induced emittance growth
60th harmonic EEHG for FLASH II, 2.5kA peak
current case 10 growth of the projected emittance
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CSR effects on EEHG microbunching
20th harmonic EEHG for FLASH II
Without CSR
2.5kA, with CSR
1.25kA, with CSR
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CSR effects on EEHG microbunching
40th harmonic EEHG for FLASH II
Without CSR
2.5kA, with CSR
1.25kA, with CSR
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CSR effects on EEHG microbunching
60th harmonic EEHG for FLASH II
Without CSR
2.5kA, with CSR
1.25kA, with CSR
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How CSR induces degradation ?

• Firstly, the electron beam radiates significant
  CSR filed in the chicane.
• Secondly, CSR-beam interaction introduces the
  energy modulation. Since the longitudinal
  variation of the CSR field, it results different
  energy chirp in different part of the beam.
• Thirdly, different parts of the electron beam
  shift to different microbunching wavelength.
• Thus, the projected microbunching bandwidth is
  broadened and the bunching factor is degraded.

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FEL performances Discussions
Initial sliced bunching factor at the radiator
entrance
20th harmonic
60th harmonic
40th harmonic
Blue 1.25kA peak current case Red 2.50kA peak
current case
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Peak power pulse energy
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Radiation power radiation phase
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D1. benchmark with CSRtrack
Hereafter, several interested issues are
stressed, we use the 20th harmonic EEHG option of
FLASH II, 2.5kA peak current case in the
following discussions.
Elegant results
CSRtrack results
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D1. benchmark with CSRtrack
With the presence of the projected type CSR
force, the bandwidth of the projected bunching
factor is broadened and the amplitude of the
projected bunching factor degraded. It is
reasonably agree with the ELEGANT results.
Meanwhile, some differences are observed, which
may be attributed by the numerical errors.
Elegant results
CSRtrack results
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D2. sensitivity on the 2nd chicane
Microbunching wavelength .vs. R56(2) With chirp
without CSR effects
Microbunching factor .vs. R56(2) Without chirp
with CSR effects
A stability of 1 of the R56 in the 2nd chicane
is required.
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D3. dependence on macro-particles
Peak power growth
Pulse energy growth
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D3. dependence on macro-particles
Initial sliced bunching
Saturated radiation pulse
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D4. longitudinal coherence
TBP0.5, close to FTL
TBP1,close to FTL
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D4. longitudinal coherence
6 times larger bandwidth than FTL
TBP1,close to FTL
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D5. EEHG fine structures
The EEHG story was preserved at each local region
of the electron beam
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D6. MBI in the large chicane
Z. Huang et al., SLAC-PUB 9538 (2002).
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D7. issues on the seed laser noise
1 RMS amplitude noise and 1 degree RMS phase
noise are introduced
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D7. issues on the seed laser noise
Only 1 RMS amplitude noise of 262nm seed laser,
no shot noise, no CSR
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D7. issues on the seed laser noise
Electron beam shot noise is not included, we use
200 slices flat-top beam
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Summary Outlook

• Robust numerical model for EEHG is developed by
  combining the existing well-benchmarked code. It
  is capable for linear energy chirp, CSR and the
  seed laser noise simulation.
• Energy chirp induces beam modulation frequency
  shift.
• CSR degrades the projected bunching a lot, but it
  has a limited effects on the sliced bunching,
  especially when the seed laser is under 100fs, or
  even shorter.
• EEHG options for FLASH II was studied for the
  first time. From the simulation, at even 60th
  high harmonic case, the strong coherent harmonic
  generation and longitudinal coherence can be
  preserved in EEHG. However, we should start from
  the 20th harmonic EEHG case.

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Summary Outlook

• Future suggestions on EEHG simulation
• How to preserve the noise level of a Gaussian
  bunch ?
• Do we need a new CSR model for EEHG modulated
  micro-structures ?
• As the energy modulation induced by a
  laser-heater, can the beam shot noise damp the
  seed laser noise effects to some extent ?
• Start2end simulation. i.e., including bunch
  compressor of FLASH LINAC and the extraction arc
  of FLASH II.
• The pulse edge of the 262nm seed laser would
  attribute the bandwidth broadening in EEHG.
• More tolerance studies, time jitter effects.
• Alternative Chicane parameters.
• CSR effects in Chicane 2, etc.

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Acknowledgments
Jianhui Chen, Meng Zhang, Bo Liu, Qiang Gu, Dong
Wang and Zhimin Dai from SINAP, Matthias Scholz,
Igor Zagorodnov, Torsten Limberg and Martin
Dohlus from DESY, Yuhui Li from European XFEL,
Yuantao Ding, Juhao Wu and Zhirong Huang from
SLAC, Jun Yan from DUKE University. Special
thanks to Dong Wang, Winfried Decking and Bart
Faatz for organization and operation of such a
collaboration.
Thanks for your attentions