What did we learn from TTF 1 FEL

What did we learn from TTF 1 FEL? P. Castro (DESY)

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 …

Index: 1) 2) 3) 4) Bunch compression Diagnostics Stability Reproducibility

1) Longitudinal bunch compression magnetic bunch compression

Long. bunch profile measurements at TTF 1 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

momentum Compression at TTF 1 time/longitudinal position (Simulation)

momentum Compression at TTF 1 time/longitudinal position (Simulation)

momentum Compression at TTF 1 time/longitudinal position (Simulation)

Coherent Synchrotron Radiation (CSR) coherent radiation for l > ssz z l L 0 R N 6 109 Power e– coherent power incoherent power sz effect Wavelength bend-plane emittance growth s DE/E = 0 Dx DE/E < 0 vacuum chamber cutoff

CSR effects in TTF 1 screen energy

CSR effects in TTF 1 screen energy

CSR effects in TTF 1 screen T. Limberg, P. Piot, et al. Tra. Fi. C 4 simulation energy

Ability to tune the length of radiation pulse demonstrated at TTF 1 compressor settings 1: short bunches compressor settings 2: long bunches long. modes: M 2 - 3 τlen ~ 50 fs long. modes: M 6 - 10 τlen ~ 100 fs sz between 30 and 100 fs 10 and 30 μm

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)

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

Photon diagnostics First spectrum of SASE at TTF 1

Photon intensity monitor: • • • large range: non-destructive position sensitive absolute calib. 50% signal decay in bunch train mostly used for SASE optimization

saturation at 98 nm (10 Sept. 2001)

saturation at 98 nm (10 Sept. 2001) fluctuations at 9 m

saturation at 98 nm (10 Sept. 2001) fluctuations at 14 m fluctuations at 9 m

saturation at 98 nm (10 Sept. 2001) fluctuations at 14 m fluctuations at 9 m statistical properties of SASE intensity extensively studied full characterization of the photon beam

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!

3) SASE stability at TTF 1 Long term stability E [ J] Stability in bunch train [ s] SASE gain ~ 106 (a factor 10 below saturation) 4 hours SASE operation

SASE stability at TTF 1 Long term stability E [ J] Stability in bunch train [ s] SASE gain ~ 106 (a factor 10 below saturation) 4 hours SASE operation

Time jitter of the electron beam Measured with streak camera by Ch. Gerth et al. (Proc. FEL Conf. 2002)

Beam stability (summary) • good stability for SASE in TTF 1 • timing jitter measured: 0. 6 ps RMS • requirements for TTF 2 minutes of timing meeting 30. 4. 03 1° ~ 0. 6 mm = 2 ps

4) Reproducibility of SASE • once SASE found/seen SASE found again after other experiments, shutdowns, etc. all parameters have to be correct • high sensitivity to magnet settings/cycling low energy / oversized magnets • change to new energy/wavelength was a challenge compression and optics changes

Wavelength tunability detuning cavities 1 st lasing changing klystron 2 settings (modules ACC 1 and ACC 2)

first lasing later lasing was found with bunches of about 3 n. C saturation was achieved with bunches of about 3 n. C