R. Bartolini

The SPARC project: a high-brightness electron beam source at LNF to drive a SASE-FEL experiment

Abstract The Project Sorgente Pulsata e Amplificata di Radiazione Coerente (SPARC), proposed by a collaboration among ENEA–INFN–CNR–Universita’ di Tor Vergata–INFM–ST, was recently approved by the Italian Government and will be built at LNF. The aim of the project is to promote an R&D activity oriented to the development of a coherent ultra-brilliant X-ray source in Italy. This collaboration has identified a program founded on two main issues: the generation of ultra-high peak brightness electron beams and of resonant higher harmonics in the SASE-FEL process, as presented in this paper.

The UV European FEL at ELETTRA: towards compatibility of storage ring operation for FEL and synchrotron radiation

Abstract The European Free Electron Laser (FEL) at ELETTRA has recently increased its maximum operating energy up to 1.5 GeV , the highest electron-beam energy used so far for an FEL. This is an important improvement in the performance of the source, increasing the extracted power at wavelengths around 200 nm and providing better beam stability and lifetime. Furthermore, this development represents a first step towards the solution of a crucial issue—the compatibility of FEL and normal synchrotron radiation operation at a user facility like ELETTRA. In this paper we discuss the most important aspects of this issue; in particular, we show that the properties of the electron beam in FEL mode can match the needs of normal synchrotron radiation experiments that require a few bunch filling of the storage ring.

Conceptual design of a high-brightness linac for soft X-ray SASE-FEL source

Abstract FELs based on SASE are believed to be powerful tools to explore the frontiers of basic sciences, from physics to chemistry to biology. Intense R&D programs have started in the USA and Europe in order to understand the SASE physics and to prove the feasibility of these sources. The allocation of considerable resources in the Italian National Research Plan (PNR) brought about the formation of a CNR–ENEA–INFN–University of Roma “Tor Vergata” study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated, leading to the SPARX proposal. We report in this paper the results of a preliminary start to end simulation concerning one option we are considering based on an S-band normal conducting linac with high-brightness photoinjector integrated in an RF compressor.

Theoretical and experimental aspects of a waveguide FEL

Abstract The dispersion properties of a guiding structure give rise to new kinematic and dynamic properties of a waveguide FEL. These new features are discussed in the small-signal small-gain approximation both in the homogeneous and inhomogeneous broadening regime, together with the outputs of a simulation code. The design of a compact waveguide FEL in the millimeter spectral range to be tested on a 5 MeV microtron FEL facility is also presented.

The Sparc project: a high brightness electron beam source at LNF to drive a SASE-FEL experiment

The Project SPARC (Sorgente Pulsata e Amplificata di Radiazione Coerente), proposed by a collaboration among ENEA-INFN-CNR-Universitadi Roma Tor Vergata- INFM-ST, was recently funded by the Italian Government. The aim of the project is to promote an R&D activity oriented to the development of a coherent ultra-brilliant X-ray source in Italy (SPARX proposal (1)). The SPARC collaboration identified a program based on two main issues: the generation of ultra-high peak brightness electron beams and experimental study of SASE-FEL process with generation of resonant higher harmonics. The SPARC project is being designed in order to encompass the construction of an advanced photo- injector producing a 150-200 MeV beam to drive a SASE-FEL in the optical range. The machine will be built at LNF, inside an underground bunker: it is comprised of an rf gun driven by a Ti:Sa laser, injecting into three SLAC accelerating sections. We foresee conducting investigations on the emittance correction(2) and on the rf compression techniques(3), which are expected to increase the peak current achievable at the injector exit up to kA level, with proper preservation of the transverse emittance. Although the system is expected to drive a FEL experiment, it can be used also to investigate beam physics issues like surface-roughness-induced wake fields, bunch-length measurements in the sub-ps range, emittance degradation in magnetic compressors due to CSR, and Compton backscattering production of sub-ps X-ray pulses.

Compact FEL activity at the ENEA-Frascati Research Center

Abstract A 5 MeV FEL facility devoted to the testing of compact FEL devices has been realized at the ENEA Research Center of Frascati. In previous experiments power up to 50 W in 4 μs pulses has been generated in a Cherenkov FEL at wavelengths ranging from 0.8 to 1.6 mm using different dielectric guides. Current activities include the testing of short-period undulators in a small size waveguide FEL designed to operate in the sub-millimeter region. Operating characteristics and predicted performance are presented.

Interplay between electron beam instabilities and storage ring FEL dynamics

We discuss the Storage Ring Free Electron Laser (FEL) operation in the presence of beam modifications due to potential well distortion and microwave instability and analyze the consequences on the FEL output power. We compare the obtained theoretical results with recent measurements at the European SR FEL at ELETTRA.

Emission of coherent radiation from a modulated electron beam

Abstract Coherent emission of radiation from a modulated electron beam passing through an undulator is described together with an analysis of the gain.

Self-consistent harmonic generation in storage ring FELs

We explore the self-induced harmonic generation in Storage Ring Optical Klystron (SR OK) FEL devices. We use a numerical code which accounts for the SR OK FEL longitudinal dynamics, includes the laser pulse propagation, and gives an accurate image ofthe phenomenology ofinstabilities associated with the laser–electron beam interplay. The coherent harmonic generation evolution is developed using the bunching parameter theory. The analysis we develop yields the turn-by-turn evolution ofthe harmonics and provides an accurate physical insight into their dependence on the intracavity laser power. The results obtained with this code are considered with mainly a Q-switched configuration evaluated for an Elettra-like facility. r 2003 Elsevier Science B.V. All rights reserved.

Super-ACO FEL oscillation with longitudinal to transverse coupled beam dynamics

The Super-ACO storage ring Free Electron Laser (FEL) has been operated using an alternative operating point characterized by a non-zero dispersion function in the undulator straight section, linking the transverse motion of the electrons to the energy spread, and by a low momentum compaction factor. The longitudinal to transverse coupled electron beam motion induces a modified dynamics of the Super-ACO FEL. The FEL characteristics, such as the FEL power, pulse duration and spectral width are presented and analyzed in terms of storage ring FEL dynamics.