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Kuske, B.C.

Paper Title Page
MOPP005 Impact of Realistic Bunch Profiles and Timing Jitter on the Output of the BESSY Low Energy FEL Line 35
 
  • B.C. Kuske, M. Abo-Bakr, A. Meseck
    BESSY GmbH, Berlin
 
 

Funding: Bundesministerium für Bildung und Forschung, the state of Berlin and the Zukunftsfonds Berlin

In present FEL designs, undulators are usually optimized for an electron bunch with properties constant along the bunch length. The central energy, emittance and other parameters are assumed not to vary from slice to slice. Unavoidable timing jitter of the photo cathode laser, and phase and amplitude errors of the RF fields in the injector and the linac result in variations in emittance, energy spread and beam dimensions along the bunch, causing a jitter in the arrival time of the electron bunch. Due to the passage through bunch compressors, the bunch shows a considerable residual energy chirp. Even assuming a perfect and on-time seed laser pulse, the changing properties along the bunch in combination with the arrival time jitter cause varying conditions for the interaction of the electron bunch with the seed laser radiation. This paper talks about how far the BESSY-FEL radiation is affected by the expected time jitter and the realistic bunch profile, and investigates counter measures. The studies are confined to the low energy FEL line generating output at l = 10nm.

 
   
MOPP006 Start-to-End Simulations for the BESSY Low and Medium Energy FEL Line Including Errors 39
 
  • B.C. Kuske, M. Abo-Bakr, K. Goldammer, A. Meseck
    BESSY GmbH, Berlin
 
 

Funding: Bundesministerium für Bildung und Forschung, the state of Berlin and the Zukunftsfonds Berlin

Contrary to storage rings, where the electron bunch properties are damped to equilibrium values due to the repeated passages through identical structures, every bunch in a single pass FEL will show individual imprints of it's passage through the linac. Based on ASTRA and ELEGANT tracking studies, realistic bunches were tracked through the BESSY-FEL undulators; the effect of timing errors of the photo cathode laser, and phase and amplitude errors of the RF fields in the injector and the linac on the FEL radiation were studied. The fluctuations of the bunch parameter due to these errors are of the order of magnitude of their variation over the bunch length, reflecting the initial electron distribution and the impact of the passed optics. The unavoidable residual energy chirp in connection with the timing jitter is of concern. The expected shot to shot variations in the FEL output are discussed.

 
   
MOPP007 Source Characterization of BESSY Soft X-Ray FEL 43
 
  • A. Meseck, M. Abo-Bakr, J. Bahrdt, B.C. Kuske
    BESSY GmbH, Berlin
 
 

Funding: Funded by the Bundesministrium für Bildung, und Forschung, the state Berlin and the Zukunftsfonds Berlin

BESSY proposes a soft X-ray free electron laser (FEL) multi-user facility. It will consist of three undulator lines, each based on cascaded High-Gain Harmonic-Generation (HGHG) scheme delivering photons in energy range of 24 eV to 1 keV. Start-to-end Simulations including error sources from the injector, and linac structure have been performed to provide realistic information about the expected radiation field (B. Kuske, FEL2005). However, the beamline designer needs to know the exact location and the size of the photon beam waist to maximize the brightness at the sample. This information can be derived from results of longitudinal propagation of the electric field distribution, which can be extracted from simulation results using the code GENESIS. The results of the Start-to-End simulation are used for realistic prediction of the photon beam properties of the BESSY Soft X-ray FEL.

 
   
MOPP028 Comparative Design Studies for the BESSY FEL Program using the MEDUSA and GENESIS Simulation Codes 91
 
  • H. Freund
    SAIC, McLean
  • M. Abo-Bakr, K. Goldammer, D. Kraemer, B.C. Kuske, A. Meseck
    BESSY GmbH, Berlin
  • S. Biedron
    ANL, Argonne, Illinois
 
 

The BESSY FEL is based on a seeded cascade of High Gain Harmonic Generation (HGHG) sections followed by an amplifier to produce coherent and stable short wavelength output. Here, we report on comparative design studies carried out using the MEDUSA [1], and GENESIS [2] simulation codes. These two codes have each been used to successfully predict a variety of FEL designs and have agreed well with a number of important experiments. In addition, they were included in a comparative study of FEL simulation [3] that reported substantial agreement between the codes for the specific configurations studied. However, these codes are based on different assumptions. GENESIS treats the particle dynamics using a wiggler-averaged orbit approximation, the transverse electromagnetic field is treated using a field solver, and harmonics are not included. MEDUSA does not use the wiggler-averaged orbit approximation to treat particle dynamics, the transverse fields are treated using a Gaussian modal superposition, and harmonics are included self-consistently. Hence, the comparative study for an HGHG cascade is important. We report the results where the parameters of each stage have been optimized.

[1] H.P. Freund et al., IEEE JQE 36, 275 (2000). [2] S. Reiche, NIMA 429, 243 (1999). [3] S.G. Biedron et al., NIMA 445, 110 (2000).