Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
SPARC_LAB present and future
Introduction
A new facility named SPARC_LAB (Sources for Plasma Accelerators and Radiation Compton with Lasers and Beams) has been recently launched at the INFN National Laboratories in Frascati, merging the potentialities of the former projects SPARC [1] and PLASMONX [2]. Ten years ago in fact, a robust R&D program on ultra-brilliant electron beam photoinjector and on FEL physics, the SPARC project, collaboration among INFN, ENEA and CNR, was approved by the Italian Ministry of Research and located at the INFN National Laboratories in Frascati.
The test facility is now operating, hosting a 150 MeV high brightness electron beam injector [3], able to operate also in the velocity bunching configuration [4], which feeds a 12 m long undulator. Observations of FEL radiation in the SASE [5], Seeded [6] and HHG [7] modes have been performed from 500 nm down to 40 nm wavelength. A second beam line has been also installed and is now hosting a narrow band THz radiation source [8]. In parallel to that, INFN decided to host a 200 TW laser that will be linked to the linac and devoted to explore laser-matter interaction, in particular with regard to laser-plasma acceleration of electrons [9] (and protons) in the self injection and external injection modes. The facility will be also used for particle driven plasma acceleration experiments, the COMB [10] experiment. A Thomson back-scattering experiment coupling the electron bunch to the high-power laser to generate a quasi coherent, monochromatic X-ray radiation is also in the commissioning phase. An upgrade of the linac energy up to 200 MeV is also foreseen by the end of 2013 by installing two new high gradient C-band structures developed at LNF in the framework of the ELI_NP collaboration [18]. A layout of the facility is shown in Fig. 1.
Section snippets
High power laser system
The SPARC_LAB high power laser system, named FLAME, has been recently fully commissioned. FLAME is based upon a Ti:Sa, chirped pulse amplification (CPA) laser able to deliver up to 220 TW laser pulses, 25 fs long, with a 10 Hz repetition rate at a fundamental wavelength of 800 nm, see Fig. 2.
The system features are characterized by a high contrast ratio (>1010) and a fully remotely controlled operation mode. It includes a front-end with pulse contrast enhancement, bandwidth control and
Thomson source
The Thomson back-scattering (TS) X-ray source [11] is foreseen to work in three different operating modes: the high-flux- moderate-monochromaticity-mode (HFM2), suitable for medical imaging, the moderate-flux- monochromatic-mode (MFM) suitable to improve the detection/dose performance [12], [13] and the short-and-monochromatic-mode (SM) useful for pump-and-probe experiments e.g., in physical-chemistry when tens of femtosecond long monochromatic pulses are needed.
The installation of the beamline
Synchronization
In order to achieve specified performances of the next future experiments at SPARC_LAB a very demanding synchronization between the subsystems is required. In particular, two laser systems (SPARC photocathode and FLAME) have to be synchronized with a relative time jitter of <500 fsRMS and <30 fsRMS for the Thomson X-ray source and Plasma acceleration experiments, respectively.
The synchronization reference is presently distributed through coaxial cables along the facility. The measured
Advanced beam dynamics experiments
With the SPARC photoinjector a new technique called Laser Comb [10], aiming to produce a train of short electron bunches, has been tested [14]. In this operating mode, the photocathode is illuminated by a comb-like laser pulse to extract a train of electron bunches injected into the same RF bucket of the gun. The SPARC laser system, based on a Ti:Sa oscillator has been upgraded for this specific application. The technique used relies on a α-cut beta barium borate (α-BBO) birefringent crystal,
Thz source
The motivation for developing a linac-based THz source at SPARC_LAB stays in the ever growing interest of filling the so-called THz gap with high peak power radiation. From simulations, the peak power expected at SPARC is in the order of 108 W. This result has been confirmed by measurements presented in [22]. The corresponding energy per pulse is of the order of tens of μJ that is well above standard table top THz sources.
Applications of this kind of source concern mainly time domain THz
Electron crystal channeling and applications
Recently we have started with a new project POSSO on studying the features of moderate-energies (0.1–1 GeV) electron beam channeling in various crystals [25]. The project aims in creating for a SPARC_LAB group both knowledge and experience for applying orientational behaviours of charged particles passage through the crystals to shape the beams (beam bending, collimation) as well as to generate a powerful X-ray and γ-radiation source (coherent bremsstrahlung, channeling radiation, parametric
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