A bunch compressor for small emittances and high peak currents at the VUV Free-Electron Laser

The Free-Electron Laser (FEL) at the TESLA Test Facility (TTF2) produces laser-like radiation in the vacuum-ultraviolet (VUV) and soft X-ray regime. To reach the minimum radiation wavelength of 6nm, bunches of electrons with an energy of 1GeV, a peak current of 2500 A and a normalized transverse emittance of less than 2 mm mrad are needed. The high peak current is achieved by compressing the electron bunches longitudinally in two magnetic chicanes. The first chicane is a modified version of bunch compressor 2 (BC2) which was used at TTF1. The second chicane is a new bunch compressor, the so called BC3. Since the charge density is very high when the bunches pass BC3, strong coherent synchrotron radiation (CSR) is emitted by the electrons and the transverse emittance of the bunch is diluted. Within this thesis different chicane layouts are compared analytically and by computer simulations to find a chicane layout which minimizes emittance dilution. A 6-bend S-shaped chicane is found to match the requirements of the VUV-FEL very well. CSR will not only lead to a growth of the transverse emittance, but also to an amplification of small modulations in energy and charge density. The dependence of the amplification on the modulation wavelength is studied for different chicane layouts and various electron bunch parameters. Computer simulations and results obtained by a theoretical model are compared. It is shown that density modulations can be amplified in BC3 by up to one order of magnitude. When the amplification in BC2 and BC3 is taken into account, the total amplification factor might reach up to two orders of magnitude.