The SPARC LAB facility

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The SPARC LAB facility at LNF consists in a conventional high brightness RF photo-injector, SPARC, and a multi-hundred terawatt laser, FLAME.
SPARC is able to produce and accelerate high brightness electron beams up to 150 MeV. Its layout is peculiar, since the first two accelerating sections are equipped with additional focusing solenoids in order to provide magnetic focusing at low energies; varying the current feeding the solenoid coils, one can tailor the focusing field along the beam path. Such solenoids are routinely used to control transverse dynamics for managing challenging SPARC working points, such as low energy RF bunch compression (velocity bunching [3]). Profiting of such particular layout, electron beams with record brightness has been produced [4], carrying up to 1 kA peak current with rms normalized emittance of about 1.5 mm mrad, to serve mainly the SASE and Seeding FEL experiments, which successfully generated FEL radiation up to saturation in the 530 nm and harmonics down to 67 nm spectral range [5]. Recently, SPARC demonstrated a novel active technique for beam generation and manipulation of ps-spaced, high brightness electron bunch trains, the so called comb-beam [6].
FLAME, whose completion has been already funded by INFN, has been successfully put into operation with the achievement of its nominal specifications. A laser pulse carrying 6 J of energy, compressed down to the nominal 25 fs pulse length, has been transported into the experiment bunker. By focusing into a supersonic gas jet in the interaction chamber, LNF recently produced self-injected bunches of electrons (INFN Self Injection Test Experiment). Such technique is already known in literature, but the results confirm that all the different part of the facility, from control to diagnostics, have been commissioned properly.
At the moment SPARC and FLAME are working as independent systems. The timing and synchronization of the photons and electron is a critical issue. The task is not simple since both electrons and photons are as long as tens of fs; jitters typical of conventional RF synchronization may prevent the correct operation. For this reason a synchronization system based on optical distribution of the reference signal will be installed shortly. Preliminary result show that the jitters between the master oscillators can be as low as 10 fs peak to peak.
A very versatile dogleg (Figure 1) is under commissioning for delivering SPARC bunches to the external injection interaction chamber; this dogleg will also serve the Thomson back-scattering X-ray source planned to operate at SPARC LAB.

Figure 1: Layout of the dogleg.

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