What did we learn from TTF1 FEL

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What did we learn from TTF1 FEL?

• P. Castro
• (DESY)

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Just to mention...

• Coupler effect in beam dynamics
• Energy oscillations in detuned cavities
• Long bunch train operation
• Gun trips/operation (covered by K. Flöttmann)
• Golden orbits in undulator

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Index

• 1) Bunch compression
• 2) Diagnostics
• 3) Stability
• 4) Reproducibility

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1) Longitudinal bunch compression
magnetic bunch compression
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Long. bunch profile measurements at TTF1
streak camera measurements of dipole radiation
with a bandpass filter 515 5 nm
coherent transition radiation interferometry
long. phase space tomography
all single meas.
average
3 mm 10 ps
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(Simulation)
Compression at TTF1
momentum
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(Simulation)
Compression at TTF1
momentum
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(Simulation)
Compression at TTF1
momentum
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Coherent Synchrotron Radiation (CSR)
coherent radiation for l gt sz
coherent power
R
e
N ? 6?109
Power
incoherent power
sz
effect
Wavelength
bend-plane emittance growth
vacuum chamber cutoff
DE/E 0
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CSR effects in TTF1
screen
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CSR effects in TTF1
screen
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CSR effects in TTF1
screen
T. Limberg, P. Piot, et al.
TraFiC4 simulation
energy
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Ability to tune the length of radiation pulse
demonstrated at TTF1
long. modes M ? 2 - 3
compressor settings 1 short bunches
tlen 50 fs
compressor settings 2 long bunches
long. modes M ? 6 - 10
tlen 100 fs
sz between 30 and 100 fs
10 and 30 µm
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Bunch compression (summary)

• long. profile well understood very short peak
  observed in agreement with photon beam
  measurements
• strong CSR effect on beam energy observed
• photon pulse length tuned between 30 and 100 fs
  (using two bunch compressors)

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2) Beam diagnostics

• long. profile monitors at resolution limit
• new techniques needed EOS, deflecting cavity,
• emittance meas. (quad. scan, wirescanner)
  initially failed
• BPMs in undulator and/or just upstream useful for
  reproducibility of SASE
• photon diagnostics were essential

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Photon diagnostics
First spectrum of SASE at TTF1
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Photon intensity monitor

• large range
• non-destructive
• position sensitive
• absolute calib. 50
• signal decay in bunch train

mostly used for SASE optimization
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saturation at 98 nm (10 Sept. 2001)
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saturation at 98 nm (10 Sept. 2001)
fluctuations at 9 m
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saturation at 98 nm (10 Sept. 2001)
fluctuations at 14 m
fluctuations at 9 m
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saturation at 98 nm (10 Sept. 2001)
fluctuations at 14 m
fluctuations at 9 m
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Essential photon beam diagnostics

• single bunch spectrum measurement wavelength and
  intensity
• intensity meas. (non-destructive preferred)
• position monitor photon beam not always on axis

integrated into control system for optimization
and for correlation studies!
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3) SASE stability at TTF1
Long term stability
Stability in bunch train
E ?J
? ?s
SASE gain 106 (a factor 10 below saturation)
4 hours SASE operation
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SASE stability at TTF1
Long term stability
Stability in bunch train
E ?J
? ?s
SASE gain 106 (a factor 10 below saturation)
4 hours SASE operation
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Time jitter of the electron beam
Measured with streak camera by Ch.Gerth et al.
(Proc. FEL Conf. 2002)
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Beam stability (summary)

• good stability for SASE in TTF1
• timing jitter measured 0.6 ps RMS
• requirements for TTF2

minutes of timing meeting 30.4.03
1 0.6 mm 2 ps
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4) Reproducibility of SASE

• once SASE found/seen SASE found again
  after other experiments, shutdowns, etc.
• high sensitivity to magnet settings/cycling
• change to new energy/wavelength was a challenge

all parameters have to be correct
low energy / oversized magnets
compression and optics changes
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Wavelength tunability
detuning cavities
1st lasing
changing klystron 2 settings (modules ACC1 and
ACC2)
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first lasing
later lasing was found with bunches of about 3 nC
saturation was achieved with bunches of about 3 nC