Compression of a 20 pC e-bunch at the European XFEL for Single Spike Operation

The production of ultra-short (fs or sub-fs long), high power, radiation pulses in the x-ray spectral region, represents a challenge for many existent SASE FELs.In order to realize single spike lasing the length of the electron bunch must be extremely small (less than a micrometer) thus it is necessary to tune the linac and magnetic chicanes near to the maximum compression point. In this setup, the final length of the electron bunch strongly depends on the non-linearity of its longitudinal phase space. The use of a third harmonic RF cavity section placed right after the injector is foreseen at the European XFEL in order to correct the longitudinal phase space non-linearity up to the third order.We describe a method for the optimization of the electron bunch compression presenting beam dynamics simulations for a 20 pC electron bunch.