Production of electron bunches with extremely small
transverse emittance is the focus of the PITZ (Photo
Injector Test facility at DESY in Zeuthen) scientific
program. PITZ is one of the leading laboratories on
generation and optimization of high brightness electron
bunches with different charges for free electron laser
(FEL) machines such as FLASH and the European XFEL.
In 2011 using a photocathode laser with a flattop temporal
profile, PITZ has revealed record low transverse
properties emittance values at different bunch charges.
However, further improvement of beam quality with
smaller emittance is foreseen using a cathode laser
system, capable of producing 3D ellipsoidal bunches.
Numerical simulations were performed to study and
compare the beam dynamics of electron beams produced
with 3D ellipsoidal and flattop laser profiles. Different
bunch charges from 20 pC up to 4 nC are considered in
the simulation, in order to find an optimum PITZ machine
setup which yields the lowest transverse emittance. In the
present paper, the simulation setup, conditions, and
results of the comparison are presented and discussed.