Meseck, A.

Paper	Title	Page
MOPPH051	Development and Application of Figures of Merit to Evaluate the Output of HGHG FEL Cascades	154
	B. C. Kuske, R. Follath, A. Meseck BESSY GmbH, Berlin
	In the design of Free Electron Lasers, parameters like the peak power and the spectral power were established as figures of merit to evaluate the FEL output quality. However, spectra obtained with FEL studies using bunches from start-to-end simulations do not have a purely Gaussian profile, so that these simple parameters can no longer be used as figures of merit. Furthermore, criteria such as the signal-to-noise ratio and the stability of the source point, which is of extreme importance for the transport of the radiation to the user experiment, should be included in the design considerations. This paper suggests different criteria and parameters to describe and compare the FEL output, which are not readily provided by the common FEL codes. An IDL code has been written, that extracts this information from the regular GENESIS output. This procedure will be used to analyze the output of the BESSY FEL.
MOPPH052	Study of a Deflecting Dispersive Chicane for BESSY Soft X-Ray FEL	158
	A. Meseck, G. Wuestefeld BESSY GmbH, Berlin
	High power, short pulse lengths and full coherence are the main parameters of the second generation free electron lasers like BESSY soft X-ray FEL. To provide radiation with these properties, cascades of HGHG stages are planned. In these stages an energy modulation is imprinted on the electron beam by seeding radiation. A dispersive section converts this energy modulation to a spatial modulation which is optimized for a particular harmonic. The following radiator is tuned to this harmonic and generates radiation with high power. The separation of the electron beam and seeding radiation after the modulation is desirable, as not only the quality of the radiator improves but also the seeding radiation itself can be used for diagnostics. A simple bending magnet leads to the separation but it causes a coupling of the longitudinal and transverse motion and could spoil the longitudinal modulation. Based on an exact linear model, a dispersive chicane is designed for one stage of the BESSY FEL which bends the electron beam without the coupling effects. The linear model will be presented and used to design a chicane. Simulations of the spatial modulation will also be discussed.
MOCAU01	The BESSY Soft X-Ray FEL: A Seeded HGHG FEL	226
	A. Meseck BESSY GmbH, Berlin
	Reproducibility, high power and short pulse length combined with variable polarization and tunable wavelength are the requirements to open new frontiers for the soft X-ray users. To provide radiation with such extraordinary properties, BESSY has been designing a seeded FEL based on high-gain harmonic-generation (HGHG) concept. The seeding with an external tunable laser ensures the reproducibility of the full-coherent radiation. The combination of so-called HGHG stages, used to down-convert the seed wavelength, and a final amplifier provides for the high power and superior spectral properties. Furthermore, the HGHG concept and the fresh bunch techniques planned for BESSY FEL mitigate the effects of parameter variation along the bunch which are expected from realistic assumptions of the Gun and LINAC structure. The design concept of the BESSY soft X-ray FEL will be presented and the stabilizing effect of HGHG stages and the benefits from the fresh bunch techniques and final amplifier will be discussed.
	Slides
	Talk
THPPH003	A High Average Power RF-Photoinjector Gun Cavity Developed for the BESSY Soft X-ray FEL	560
	F. Marhauser, M. Dirsat, V. Duerr, A. Meseck, R. Richter, E. Weihreter BESSY GmbH, Berlin G. Asova, J. W. Baehr, H.-J. Grabosch, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, A. Oppelt, B. Petrosyan, L. Staykov, F. Stephan DESY Zeuthen, Zeuthen O. Kalekin Humboldt Universität zu Berlin, Berlin J. R. Roensch Uni HH, Hamburg F. Tonisch DESY, Hamburg
	A 1.3-GHz, high duty factor, high-repetition-rate rf photoinjector gun cavity has been developed at BESSY. RF conditioning and high-power tests have been performed at the Photoinjector Test Facility at DESY Zeuthen (PITZ). The measurement results will be presented in this paper.