| Paper |
Title |
Page |
| MOPC019 |
Velocity Bunching at FLASH
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112 |
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- T. Limberg, B. Beutner, W. Decking, M. Huening, M. Krasilnikov, M. Vogt
DESY, Hamburg
- O. Grimm
Uni HH, Hamburg
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The vacuum-ultra-violet free electron laser in Hamburg (FLASH) is a linac driven SASE-FEL. High peak currents are, in routine operation, produced using magnetic bunch compression chicanes. Longitudinal dispersion in these chicanes allow bunch length changes of relativistic electron beams. For low energy electron beams (~5 MeV), the velocity dependence on electron energy can be utilized for bunch compression. Since strong bunch compression at low beam energies gives rise to strong space charge interactions which has an impact on, for instance, beam emittance and is therefore not suitable for full compression to the kA peak currents needed for SASE operation. Moderate velocity bunching, however, might be used to optimize the total bunch compression system of FLASH or the European XFEL. Experiments on the velocity bunching process at FLASH are presented here. Results on bunch length and transverse emittance measurements are discussed and compared with numerical tracking calculations.
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| TUPP018 |
Impact of Electromagnetic Fields in TESLA RF Modules on Transverse Beam Dynamics
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1568 |
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- E. Prat, W. Decking, M. Dohlus, T. Limberg, I. Zagorodnov
DESY, Hamburg
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Transverse electric fields in TESLA rf modules exist on one hand because of deformations of the longitudinal accelerating field in the presence of rf structure misalignments or in the vicinity of asymmetrically machine parts like input couplers. On the other hand, the beam itself induces transverse wake fields if it does not travel through the center of a perfectly rotationally symmetric structure. Transverse deflecting fields deflect beam particles. The average deflection causes a change in the beam trajectory; the phase dependence of the transverse field leads to a variation of the transverse kick along the longitudinal position of the bunch and thus in general to a change in projected emittance. If the strength of the transverse field component varies along the transverse direction itself, slice emittance will be also affected. We will present the amplitudes and spatial variations of transverse fields generated by the mechanisms described above, and discuss their impact on beam trajectories and shape.
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| THPC111 |
Simulation ofμBunching Instability Regimes in the FLASH Bunch Compressors
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3236 |
| |
- M. Vogt, T. Limberg
DESY, Hamburg
- D. H. Kuk
The University of Texas at Austin, Austin, Texas
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The bunch compression scheme for the European XFEL will operate in a regime in which, at least without additional energy spread introduced by a laser heater, theμbunching effect proposed in the literature may severely degrade the performance of the FEL. However, clear, unambiguous signals of theμbunching effect have not yet been seen neither in simulation nor experiment. The proposedμbunching effect amplifies initial current modulations by interleaved application of longitudinal collective energy kicks and transformations of energy modulation into current modulation in magnetic chicanes. In order to establish a parameter regime for experimental verification ofμbunching at the FLASH VUV-FEL at DESY, we have scanned the relevant part of the parameter space using a linear, quasi-analytic, noise-free gain-model and complemented this with particle tracking simulations. The tracking was performed using interleaved runs of ASTRA for acceleration modules and CSRTrack for the chicanes, automatically linked by the start-to-end simulation tool box Gluetrack.
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