P. L. Ottaviani

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.

Two harmonic undulators and harmonic generation in high gain free electron lasers

We consider an undulator scheme to enhance harmonic generation in high gain free electron lasers. The configuration we consider consists of an undulator providing an on axis field oscillating in both transverse directions, with relatively integer multiple spatial periods. We discuss the spectral properties of the radiation emitted by relativistic electrons crossing this undulator and derive the equations describing the free electron laser evolution. We show that a device, exploiting such an undulator configuration, is a fairly useful tool to obtain simultaneous laser power at different harmonics. The analysis of the system evolution is achieved with two different simulation codes.

Nonlinear harmonic generation in high-gain free-electron lasers

We reconsider the derivation of semianalytical expressions providing the most significant aspects of the high-gain free-electron laser dynamics. We obtain new expressions for the growth of the laser power, of the e-beam-induced energy spread, and of the higher-order nonlinearly generated harmonics. The procedure we employ, based on theoretical ansatz and fitting methods, allows the determination of crucial quantities like the expected harmonic output power and its dependences on the e-beam parameters.

European project to develop a UV/VUV free-electron laser facility on the ELETTRA storage ring☆

Abstract The main features and novel technical aspects of a new European project to integrate a free-electron laser on an existing “third generation” synchrotron radiation user facility are described, including the design of the optical cavity and undulator, the electron beam characteristics and a first assessment of the predicted laser performance.

Design considerations on a high-power VUV FEL

We explore the feasibility conditions of a high-power EEL operating in the VUV region (below 100 nm) and exploiting a coupled oscillator triplicator configuration. A high quality beam from a linac is passed through a EEL oscillator and produces laser radiation at 240 nm. The same beam is extracted and then injected into a second undulator tuned at the third harmonic of the first. The bunching produced in the oscillator allows the start up of the laser signal in the second section which operates as an amplifier. We discuss the dynamical behavior of the system and the dependence of the output power on the characteristics of the e-beam and of the oscillator. The possibility of enhancing the output power, adding a tapered section to the second undulator, is finally analyzed. >

Design considerations for x-ray free electron lasers

We develop design considerations on the possibility of generating free electron laser radiation in the x-ray region of the spectrum (50–60 A), by exploiting a frequency multiplier scheme. We propose a free electron device consisting of a relatively low energy linac (750 MeV) and three sections: an oscillator at 150 nm, an amplifier tuned at the fifth harmonic of the first and a second amplifier operating at a subharmonic of the second amplifier. The seedless amplification is ensured by the e-beam bunching, induced in the oscillator and in the second section, which plays the role of amplifier and modulator. We also explore the possibility of overcoming the problems associated with the bunching efficiency dilution, due to intracavity saturation of the first section, by discussing the regeneration of the bunching by the use of a cavity dumping, realized with a suitable e-beam energy or cavity detuning modulation.

A model for the saturation of a storage ring free electron laser

Abstract The dynamical properties of a storage ring free electron laser oscillator are reproduced using a model combining three different saturation mechanisms: laser induced energy spread of the e-beam, associated bunch lengthening and longitudinal synchronism between laser and electron pulses. The stationary output power is shown to be always linked to the power emitted via synchrotron radiation in one machine turn by the circulating e-beam.

Semi-analytical model of self-amplified spontaneous-emission free-electron lasers, including diffraction and pulse-propagation effects

We use the high-gain free-electron laser logistic equation to describe the field evolution from spontaneous emission to saturation in the self-amplified spontaneous-emission regime. The model we present is capable of including the effects of diffraction, beam qualities, and pulse propagation.

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.

Parametrization of the electron beam induced energy spread in free electron laser dynamics

We discuss a formula providing a parametrization of the energy spread induced on the electron beam in a free electron laser (FEL) oscillator. The formula we propose depends on the intracavity laser intensity and on the saturation intensity of the system. We show that such a parametrization can usefully be exploited in the analysis of FEL storage ring dynamics.