Activities on High Brightness Photo-injectors at the Frascati Laboratories, Italy

An intense activity on high brightness photo-injectors for SASE-FEL experiments and facilities, is being carried out, since 2003, in the Research Site of the INFN Frascati Laboratory, Rome, in collaboration with CNR and ENEA. SPARC is the 150 MeV photo-injector, in advanced phase of commissioning at LNF. The electron beam, which drives a 530 nm FEL experiment, is being characterized in terms of emittance, energy spread, peak current. The matching with the linac confirmed the theoretical prediction of emittance compensation based on the “invariant envelope” matching. The demonstration of the “velocity bunching” technique is in progress too. The SPARC photo-injector is the test facility for the soft-X FEL project named SPARX [1], that is based on the generation of ultra high peak brightness electron beams at the energies of 1.2 and 2.4 GeV generating radiation in the 1.5-13 nm range. SPARX will be realized in the TorVergata University campus. In this paper we report the experimental results obtained so far with SPARC and the design status of the SPARX project. THE SPARC TEST FACILITY The INFN Frascati Laboratory (LNF) and the ENEA Frascati Research Center (CRF) are involved since 2003 in the development and the commissioning of the S-band photo-injector SPARC, aimed to generate high brilliance electron beams to drive SASE-FEL experiments in the visible and UV region, with a laser-seeding process. Moreover, SPARC will be the pre-injector of SPARX, the new high brightness electron linac to generate SASE-FEL radiation in the 40 to 0.6 nm wavelength range, that will be built in the campus of the Tor-Vergata (TV) Rome University, 4 km airline from LNF. The SPARC research program is scheduled in two phases. The first one is concluded and consisted in characterizing the electron beam, photo-emitted at 5.6 MeV by the cathode of a S-band RF gun, illuminated by Ti-Sa Laser beam pulses [2]. The results of the first commissioning phase are reported in [3]. The second phase, still in progress, foresees a detailed analysis of the beam matching with the linac to confirm the emittance compensation theory, based on the “invariant envelope” matching [4] and to verify the emittance compensation with the “velocity bunching” (VB) experiment [5]. SASE and SEEDING experiments are also foreseen by the end of 2008. SPARC will also allow to study ultra-short beams physics, plasma wave-based acceleration, and to generate advanced X-ray beams via Compton backscattering.