INVESTIGATIONS ON THE IMPACT OF MODULATIONS OF THE TRANSVERSE LASER PROFILE ON THE TRANSVERSE EMITTANCE

The Photoinjector Test Facility at DESY, Zeuthen site (PITZ), was established to develop and optimize electron bunch sources for superconducting linac-based free electron lasers like FLASH or the future European XFEL. The successful operation of such FELs requires electron bunches of very low normalized transverse emittance of the order of 1 mm mrad at a charge of 1 nC. One key issue for obtaining low-emittance electron bunches is the possibility to influence the electron bunch properties by varying the photocathode laser pulse characteristics. This contribution focuses on the discussion of deviations from the optimum transverse shape of a circularflat-top. Different types of modulations are added to the flat-top and the resulting change in transverse emittance will be discussed based on beam dynamics simulations.