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| Home > Publications database > Longitudinal Electron Bunch Shape Reconstruction from Form Factor Modulus based on Spectrally Resolved Measurements of Coherent Transition Radiation |
| Book/Report/Dissertation / PhD Thesis | PUBDB-2018-03950 |
; ;
2018
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2018-03950
Report No.: DESY-THESIS-2018-031
Abstract: Free-electron lasers, like the free-electron laser in Hamburg (FLASH), provide brilliant photon pulses on a femto-second time scale. Generation of this pulses is done in a high-gain self-amplified spontaneous emission or seeded FEL process. This FEL process is driven by electron bunches with high peak current and high quality. The photon pulse length is determined by the electron bunch length inside the accelerator. A controlled and reproducible setup of accelerator parameter for certain photon pulse settings requires longitudinal electron bunch diagnostics which is able to measure electron bunch duration on the femto-second time scale. Currently, two diagnostic techniques, one in time domain and the other in frequency domain, can be used routinely for this task. The time domain diagnostics utilizes a transverse deflecting cavity and the other spectral resolved intensity measurements.Longitudinal form factor is the Fourier transform of the longitudinal electron bunch density distribution. The form factor modulus is accessible from spectral resolved intensity measurements, while the phase information is lost. This loss of phase information prevents a unique determination of the longitudinal electron bunch density by application of the inverse Fourier transform to the longitudinal form factor. Instead, phase reconstruction techniques have to be used in order to obtain the longitudinal electron bunch density distribution.A new time profile reconstruction algorithm is presented in this thesis. This algorithm is a further development of the Gerchberg-Saxton iterative reconstruction algorithm. The new algorithm is based on statistical and clustering analysis of a results pool, which is generated using multiple independent iterative reconstruction algorithm starts.Behaviour of the new time profile reconstruction algorithm is tested on model profiles and on measurements at FLASH. Further, a comparison with another time profile reconstruction technique based on the Kramers-Kronig relation is done.Since reconstruction of time domain profiles from spectral resolved intensity measurements suffer from ambiguities due to loss of phase information, a comparison of longitudinal diagnostics utilizing spectral resolved intensity measurements of coherent transition radiation with complementary time domain diagnostics technique has been performed at FLASH.
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