Paper  Title  Page 

MOP060  RFTweak 5  An Efficient Longitudinal Beam Dynamics Code  176 


The shaping of the longitudinal phase space in bunch compression systems is essential for efficient FEL operation. RF systems and selffield interactions contribute to the overall phase space structure. The design of the various facilities relies on extensive beam dynamics simulations to define the longitudinal dynamics. However, in everyday control room applications such techniques are often not fast enough for efficient operation, e.g. for SASE tuning. Therefore efficient longitudinal beam dynamics codes are required while still maintaining reasonable accuracy. Our approach is to precalculate most of the required data for selffield interactions and store them on disc to reduce required online calculation time to a minimum. In this paper we present the fast longitudinal tracking code RFTweak 5, which includes wakes, space charge, and CSR interactions. With this code the full European XFEL with a 1M particles bunch is calculated on the order of minutes on a standard laptop. Neglecting CSR effects this time reduces to seconds.  
Poster MOP060 [0.799 MB]  
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TUC03 
Low Slice Emittance Preservation in Bunch Compressors  


Minimize the dilution of the beam emittance is crucial for accelerators, and in particular for Free Electron Lasers, where the length of the machine and the finally the efficiency of the lasing process depend on it. At the SwissFEL Injector Test Facility we measured unexpected slice emittance increase after compressing the bunch also for moderate compression factors. We experimentally characterized the dependency of this phenomenon on the beam and machine parameters relevant for the compression. In order to qualitatively reproduce all the measurements outcomes it was necessary to use a 3D beam dynamic model along the bunch compressor including coherent synchrotron radiation. After excluding space charge forces, spurious dispersion and microbunching instability as possible sources for the observed emittance dilution, we identified the coherent synchrotron radiation and its interaction with the electron beam as the main responsible of the phenomenon. We also studied both experimentally and with simulations the contribution of the mismatch along the bunch to the longitudinal variations of the slice emittance. These experimental and theoretical investigations allowed a reoptimization of the injector. Typically with 150 A peak current, 200 pC charge it was possible to reach less than 200 nm.rad for the central slice with a moderate increase up to less than 300 nm.rad on the tails.  
Slides TUC03 [1.395 MB]  
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TUP068  Electron Beam Phase Space Tomographie at the European XFEL Injector  515 


Transverse emittances as well as the energy spread and the peak current of the electron bunches are important parameters for highgain free electron lasers such as the European XFEL. Investigations of the 6D phase space characterisation would give important indications to optimise the beam quality for SASE operation. The injector of the European XFEL includes, inter alia, a laser heater, a transverse deflecting cavity, a spectrometer, a diagnostic section with four OTR screens as well as several quadrupole magnets. In this paper, we will discuss the possibilities to characterise the 6D phase space of the electron beam in the injector of the Eurpean XFEL.  
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