We investigate the upgrade of Elettra 2.0 to radio-frequency transverse deflecting cavities generating a steady-state vertical deflection of selected electron bunches. The study demonstrates the feasibility of 1 to few ps-long x-ray pulses at MHz repetition rate provided simultaneously to several beamlines, and transparent to the standard multi-bunch operation. The short pulse exhibits total flux at 1-10% level of the standard single bunch emission, and transverse coherence preserved in both transverse planes up to approximately 0.5 keV.

The upgrade of the single cascade FEL-1 of the FERMI free-electron laser, aiming at implementing operation either in Echo Enabled Harmonic Generation (EEHG) or in High Gain Harmonic Generation (HGHG) mode, has started. We have recently modified the layout in order to crate the space required for the installation of the large dispersive section needed for the EEHG scheme. As a result, the radiator has been separated by a 10-meter long drift from the modulator, where the interaction between electron bunch and seed laser takes place. The setup will be completed by the end of the first semester of 2023 and users operations are expected to start shortly afterwards. In this contribution, we present a status report of the FEL-1 upgrade process, focusing in particular on the results obtained during the commissioning.

We present an overview of the FERMI seeded free electron laser (FEL) facility located at the Elettra laboratory in Trieste, Italy. FERMI, in operation with both FEL lines FEL-1 and FEL-2 since 2012, covers the spectral range between 100 nm and 4 nm with light characterized by variable polarization, narrow spectral width, stable intensity and central wavelength. A series of infrastructure upgrades have been proposed in recent years to keep the facility in a world-leading position. The upgrade includes profound modifications of the linac and the two FERMI FELs with the ambition to extend the performance of the FEL and the control of the light produced to include the K edges of N and O and the L edges of transition metals. Recently, new accelerating section allowed an increase of the beam energy of about 100 MeV and the configuration of the first FEL-1 has been revamped. The FEL has been changed into an echo-enabled harmonic-generating FEL, and commissioning of this new FEL is underway.

An upgrade project is ongoing at Elettra Sincrotrone Trieste for a 4th-generation storage ring light source called Elettra 2.0. The new machine poses new challenges in terms of performance of the accelerator and sub-systems. One concern, currently under investigation, is about the effects of the passive superconducting third harmonic cavity on the stored beam due to the presence of a dark gap in the beam filling pattern. A simulator based on an analytical frequency-domain model was developed to evaluate the variation of the synchronous phase and synchrotron frequency along the bunch train, as well as the distortion of the bunch profile. Experiments have been carried out in the present Elettra storage ring to characterize the harmonic cavity and to measure the ef-fect of transient beam loading by using the longitudinal multi-bunch feedback system. An ongoing benchmarking of the model and experimental results is reported.

The accelerator upgrades of SLS and Elettra will use newly designed kickers adapted for their small aperture beam pipes. The striplines of the transverse kickers conform closely to the aperture of the beam pipe with special grooves to avoid synchrotron light on the blades. The multitude of trapped higher order modes, caused by a high beam pipe cut-off frequency and dangerous in terms of stability and heat up, is suppressed by lossy silicon carbide dampers. The devices feature integrated pumping ports. The transverse shunt impedance improves by a factor of four compared to the current SLS/Elettra kicker. The longitudinal kicker is a heavily coupled cavity at 1.875 GHz (3.75 * RF) with four input and four output couplers for driver and loads. A nose cone design optimizes the shunt impedance resulting in a 20% improvement over the current SLS/Elettra kicker. Also here, the high cut-off frequency of the beam pipe caused problematic higher order modes, which needed to be damped by higher order mode couplers. A dedicated field sensor pickup will be used to synchronize the feedback to the bunch train.