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SPARC-X is a two branch project consisting in the SPARC test facility dedicated to the development and test of critical subsystems such as high brightness photoinjector and a modular expandable undulator for SASE-FEL experiments at 500 nm with seeding, and the SPARK facility aiming at generation of high brilliance coherent radiation in the 1.5-13 nm range, based on the achieved expertise. The projects are supported by MIUR (Research Department of Italian Government) and Regione Lazio. SPARC has completed the commissioning phase of the photoinjector in November 2006. The achieved experimental results are here summarized together with the status of the second phase commissioning plans. The SPARK project is based on the generation of ultra high peak brightness electron beams at the energy of 1 and 2 GeV generating radiation in the 1.5-13 nm range. The construction is at the moment planned in two steps starting with a 1 GeV Linac. The project layout including both RF-compression and magnetic chicane techniques has been studied.

We discuss the design elements of a compact free electron laser device, operating, in an oscillator–amplifier configuration, up to the soft X-ray region. We show that, the source can provide radiation from extreme UV to soft X-ray region, with significantly large output peak and average laser power with undulator lengths not exceeding 7 m.

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.

The status of the art of the VUV-X-ray FEL sources, the limit of the relevant technologies and the future perspectives are analysed. Possible strategies aimed at developing the design of a road map toward very short wavelengths, very high brilliance and very short pulses are discussed. Within such a framework we report and comment on the proposed devices.

The generation of harmonics through a nonlinear mechanism driven by bunching at the fundamental has sparked interest as a path toward enhancing and extending the usefulness of an x-ray free-electron laser (FEL) facility. The sensitivity of the nonlinear harmonic generation to undulator imperfections, electron beam energy spread, peak current, and emittance is important in an evaluation of the process. Typically, linear instabilities in FELs are characterized by increased sensitivity to both electron beam and undulator quality with increasing harmonic number. However, since the nonlinear harmonic generation mechanism is driven by the growth of the fundamental, the sensitivity of the nonlinear harmonic mechanism is not expected to be significantly greater than that of the fundamental. In this paper, they study the effects of electron beam quality, more specifically, emittance, energy spread, and peak current, on the nonlinear harmonics in a 1.5-{angstrom} FEL, and show that the decline in the harmonic emission roughly follows that of the fundamental.

We show that Free Electron Lasers (FEL) operating with storage rings may counteract beam instabilities of the Saw Tooth (STI) type. We use a model based on a set of equations that couple those describing the FEL evolution to those accounting for the STI dynamics. The analysis provides a clear picture of the FEL-STI mutual feedback and clarifies the mechanisms of the instability inhibition. The reliability of the results is supported by a comparison with fully numerical codes.

The basic principles of free electron generators of coherent radiation and the practical considerations related to the development of far infrared and sub-millimeter wave sources are discussed in this paper. The attention is focused on compact devices, which reduce the size and cost issue. A review of the main results obtained at the Frascati FEL Facility is presented together with the planned experiments.

The method of the generating function is exploited to derive analytical expressions of integrals involving products of Hermite polynomials. It is shown that, this type of integrals, often appearing in problems relevant to Free Electron laser or optical radiation confinement can be expressed in terms of generalized Hermite polynomials. The possibility of extending the method to the case of Bessel function is also touched on.

We explore the analytical dependence of the free-electron laser (FEL) saturated power on the cavity detuning and discuss the dependence of the higher harmonics generated power on this quantity. We show that a suitable modulation of the cavity detuning may provide a pulsed behaviour of the laser, superimposed to the natural mode locking. The new temporal characteristics of the laser are discussed and it is shown that they can be controlled by controlling the cavity-length modulation period. We also study the effect of this modulation on the harmonic generation. The possibility of extending the same mechanism to a free electron laser operating with a storage ring is finally discussed and we show that, under certain conditions, it may modify the characteristics of the stationary configuration.

We present an analysis of the dynamical behavior of a storage-ring FEL oscillator with the inclusion of the microwave longitudinal instability. We prove that the FEL interaction provides a damping mechanism for this type of instability and we discuss the relevant physical interpretation. We also show that the numerical model, exploited to include the microwave instability effects, reproduces the relevant phenomenology and yields a dynamical basis for the Boussard criterion.

We discuss a simple model for the evolution of a Storage-Ring (SR) FEL operating in the optical-klystron (OK) configuration. We analyze the OK gain formula and introduce the parametrizations which account for the inhomogeneous broadening and saturation effects. We also derive a parametrization for the induced energy spread. The OK SR FEL evolution is then described by two coupled rate equations which accounts for the evolution of the intracavity power and the associated e-beam heating and damping. The model allows the derivation of the stationary output and intracavity power and is also a flexible tool for the system optimization. The analytical results are confronted with the available experimental data and the agreement is found more than satisfactory.

The dynamical behaviour of the free-electron lasers is investigated by using appropriate scaling relations valid for devices operating in the low and high gain regimes, including saturation. The analysis is applied to both single passage and storage ring configurations. In the latter case the interplay between the interaction of the electron beam with the laser field and with the accelerator environment is investigated. In particular we discuss the effect of FEL interaction on the microwave instability.

We study the modifications induced on the longitudinal dynamical behaviour of an e-beam circulating in a Storage-Ring (S.R.) and undergoing a FEL interaction. We discuss the low gain amplifier case and, using the Fokker-Planck equation, evaluate the effect of the FEL interaction on the longitudinal damping time, which is shown to be a function of the detuning parameter and of the intensity itself. We develop a self-consistent model of the S.R. FEL dynamics capable of including saturation, induced energy spread and damping time modifications. The model is shown to be particularly useful to investigate the system evolution and the interplay between the various features causing the saturation of the device.

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.

SPARC and SPARX are two distinct phases of an Italian FEL SASE project involving different national institutions. SPARC is a high gain FEL project aimed at developing a source of visible and VUV radiation exploiting SASE mechanisms. A 150 MeV Linac will provide a high quality e-beam to generate high brilliance FEL radiation at visible region at the fundamental wavelength and at VUV wavelengths with the harmonics. SPARC will allow to investigate velocity bunching mechanisms in the bunch compressor and coherent harmonic generation in the undulators. SPARX is a project aimed at the realization of an FEL SASE source operating at 13.5 and 1.5 nm in two separate undulators channels with a 2.5 GeV electron beam. SPARX development is expected to take profit of the SPARC activities and part of the equipment. We describe here the main features of these two projects including accelerators system, FEL sections and applications.

The status of the commissioning of the 25 MeV superconducting (SC) linac LISA is reported. Some crucial steps toward routine operation of the 1 MeV injector and the cryogenic system have been done. The problems related to the diagnostic setup for spontaneous emission measurement and cavity alignment are also presented.

The waveguide operation of a compact free-electron laser driven by a 2.3-MeV S-band microtron is reported. Power up to 1 kW in 4-\ensuremath{\mu}s pulses has been generated at wavelengths in the range between 2.1 and 2.6 mm. Novel tuning features and temporal characteristics of the emitted radiation, related to the bunched nature of the electron beam and to the dispersive effect of the waveguide, have been observed.

In this note we explore the conditions under which synchrotron radiation can be used to trigger a photocathode gun. We show that such a solution offers in principle the possibility of operating with a pulsed electron beam filling all the buckets of the accelerating radio frequency. Some comments on the e-beam characteristics are also presented.

We present the issue raised by electron cyclotron resonance heating for the present development of Fusion Reactors. The possibility of realizing a Free Electron Laser operating in the range 220–450 GHz is discussed also in view of heating in high magnetic field Tokamak

We report the progress of the superconducting linac LISA at LNF (Frascati National Laboratories) and the status of the FEL experiment. The design of the optical cavity is presented.

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.

One of the more promising plasma heating and current drive methods in magnetic confinement fusion machines is the “electron cyclotron resonance heating (ECRH)” at millimetric and submillimetric wavelengths. Radiation sources delivering average power up to many megawatts per unit with total efficiency on the order of 30–40% are required. In this article the main problems and key issues related to the realization of FEL devices, well suited for this kind of applications, are analyzed.

We report the observation of coherent emission from a Cherenkov FEL driven by a 5 MeV radio frequency microtron. Power up to 50 W in pulses of 4 μs duration has been generated at wavelengths of 1.6 and 0.9 mm using two different dielectric loaded waveguides.

A 50 periods long hybrid permanent magnet undulator is being realized at Ansaldo Ricerche for the LISA FEL experiment of the INFN, Frascati, Italy [1]. An innovative design of the mechanical structure and an electronic control system have been developed in order to accurately position the jaws without requiring very tight mechanical tolerances in the manufacturing of the driving components. The mechanical design has been optimized by performing an accurate structural analysis with the ANSYS code. The control system checks the parallellism between the jaws during the gap variation and restores it automatically. Besides, it changes the current of the correction coils to minimize the dipole field integral at each gap. The security system to guarantee the safe operation of the device is also described.

The potential advantages and the physical properties of several electron-transparent mirrors (e.g., metal meshes, thin foils, pierced mirrors, and Bragg reflectors) to be used in infrared free-electron laser resonators are reviewed. The conditions under which the effect on the electron beam quality can be kept small are discussed, and experimental results on the angular spread produced by a 2.5- mu m-thick metal mesh on a 5 MeV electron beam are presented. The experimental test of a resonator with two different electron transparent output couplers is reported. >

The kinematic and dynamic properties of a waveguide FEL are described in the small signal small gain approximation in both the homogeneous and inhomogeneous regimes.

A program to construct a test superconducting electron linear accelerator (LISA) is in progress at Frascati INFN National Laboratories. The electron beam will be used to realize an FEL in the infrared region (11–18 μm) in collaboration with a group of ENEA-CRE Frascati. The electron beam parameters and their relation to the expected performances of the FEL are discussed. Some future developments — energy recovery, energy doubling — are briefly presented.

A far-infrared-wavelength, rf-accelerator-driven, metal-grating free-electron laser (MG-FEL) experiment is proposed. The resonator will be an open planar structure, loaded with a narrow strip grating, and terminated with cylindrical section mirrors.

In this paper we present simple and general formulae for the FEL gain in the pulsed regime including both the longitudinal mode coupling and the lethargy effect. Such relations, obtained from a numerical integration of the pulse propagation equations, are then compared to similar expressions obtained analitycally in the limiting case of the long bunch approximation and the agreement is shown to be excellent.

The first phase of the SPARX project, now funded by MIUR (Research Department of Italian Government), is an R&D activity focused on developing techniques and critical components for future X-ray FEL facilities. This project is the natural extension of the activities under development within the ongoing SPARC collaboration. The aim is the generation of electron beams characterized by an ultra-high peak brightness with a linear accelerator based on the upgrade of the existing Frascati 800 MeV LINAC and to drive a single pass FEL experiment in the range of 3-5 nm, both in SASE and SEEDED FEL configurations, exploiting the use of superconducting and exotic undulator sections. In this paper we discuss the present status of the collaboration.

The current trends and recent developments of Free Electron Lasers in the two spectral regions laying at the boundaries of the electromagnetic spectrum are reviewed in this paper.

High gain free electron laser devices, operating in the self amplified spontaneous emission regime, are under construction and was designed as the next generation of synchrotron radiation sources. In this paper we discuss the relevant physical aspects and derive simple relations for laser and higher order harmonic power, which can usefully be exploited in the preliminary design of these sources

A hybrid permanent-magnet undulator is under development in Ansaldo Ricerche for the LISA FEL experiment. The criteria adopted to optimize the magnetic and mechanical design of the undulator and the results of field measurements on an eight-period prototype will be discussed. The device used for measuring the permanent-magnet blocks and the code developed for their sorting will be described.

An undulator free-electron-laser experiment (U-FEL) is under way at the ENEA-Frascati Center. The U-FEL employs a 20 MeV microtron as electron-beam source and operates in the middle infrared region around 30 μm. Recent results on the spontaneous-emission measurements are discussed.

SPARC and SPARX are two different initiatives toward an X-ray FEL SASE source at LNF. SPARC is a high gain FEL project devoted to provide a source of visible and VUV radiation while exploiting SASE mechanism. An advanced Photo-Injector system, emittance self-compensating RF-gun plus a 150 MeV Linac, will inject a high quality e-beam into the undulator to generate high brilliance FEL radiation in the visible region at the fundamental wavelength, (530 nm). The production of flat top drive laser beams, high peak current bunches, and an emittance compensation scheme will be investigated together with the generation of higher harmonic radiation in the VUV region. SPARX is the direct evolution of such a high gain SASE FEL towards the 13.5 and 1.5 nm operating wavelengths, at 2.5 GeV. The first phase of the SPARX project, fiinded by Government Agencies, will be focused on R&D activity on critical components and techniques for future X-ray facilities as described in this paper.

We use a semi analytical model to investigate the mechanisms underlying the saw tooth instability dynamics in storage rings. We discuss its interplay with other effects, such as the multiple Touschek scattering and derive an upper limit for the power emission associated with such an instability.

We present a phenomenological treatment of free-electron laser storage ring saturation dynamics. The model includes longitudinal instabilities, Touschek intrabeam scattering, and nonzero off-energy-function contributions. The model predictions are compared with Super ACO experimental results and the agreement is shown to be satisfactory.

SPARC and SPARX are two different initiatives toward an ItalianFreeElectronLaser (FEL) source operating in theSelfAmplifiedSpontaneousEmission (SASE) mode, in which several national research institutions are involved. SPARC is a high gain FEL project devoted to provide a source of visible and VUV radiation while exploiting the SASE mechanism. An advanced Photo-Injector system, emittance compensating RF-gun plus a 150 MeV Linac, will inject a high quality e-beam into the undulator to generate high brilliance FEL radiation in the visible region at the fundamental wavelength, (∼500 nm). The production of flat top drive laser beams, high peak current bunches, and emittance compensation scheme will be investigated together with the generation of higher harmonic radiation in the VUV region. SPARX is the direct evolution of such a high gain SASE FEL toward the 13.5 and 1.5 nm operating wavelengths, at 2.5 GeV. To get the required value for the bunch peak current, Ipeak≈ 2.5 kA, the “hybrid” scheme, RF-compression stage plus magnetic chicane, is analyzed and compared with the more standard double stage of magnetic compression. The two options are reviewed considering the tolerance to the drive laser pulse phase jitter.

The longitudinal dynamics of an electron beam circulating in a storage ring and undergoing a FEL interaction is discussed with specific reference to the low gain amplifier case. We exploit the Fokker-Planck equation and analyze the multipolar components of the longitudinal electron motion. One of the major achievements of the analysis is relevant to the longitudinal damping time, which is shown to be interaction dependent, i.e. a function of the FEL detuning parameter and laser intensity.

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, bringing 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 a RF compressor.

The hybrid permanent magnet undulator for the LISA-FEL (free electron laser) experiment (INFN, Frascati, Italy) has been designed and manufactured. A computerized driving system has been developed in order to lighten the mechanical structure and gain accuracy in positioning of the jaws during gap variation. The NdFeB permanent magnet blocks have been measured and sorted in order to reduce magnetic field errors along the undulator axis. The field integrals are minimized by the electronic control, which feeds the correction coils with a gap-dependent current. The first results of mechanical tests and magnetic field measurements confirm the good performance and reliability of the device. >

The mechanism of nonlinear harmonic generation in the exponential gain regime, which is driven by bunching at the fundamental wavelength, may provide a path toward both enhancing and extending the usefulness of an x-ray free- electron laser (FEL) facility. Related exotic generation schemes, which exploit properties of harmonic production in various undulator topologies, have been discussed both in the past and more recently. Using three different numerical simulation codes, we explore the possible utility of such schemes (e.g., harmonic afterburners and biharmonic undulators) at future light source facilities.

Nonlinear harmonic generation can be a very useful and important phenomenon for single-pass free-electron lasers (FELs) operating in the high-gain regime. Strong bunching at the fundamental wavelength and its associated higher harmonic content allow significant radiation at shorter wavelengths to be emitted without serious effects upon the output power at the fundamental. Here, we analyze the relative sensitivities to beam quality variations of the output fundamental and harmonic powers for a visible-wavelength FEL operating in the high-gain regime.

We report the first operation of a compact free-electron laser at wavelengths in the range between 2 and 2.6 mm with an output power up to 1 kW in 4 μs pulses. The innovative characteristic of this device, driven by a 2.3 MeV microtron, is its considerable small size, obtained by using a short undulator with a 2.5 cm period and a length of 22.5 cm.

The stabilization of nonlinear excitations by noise is a topic of fundamental importance in many physical problems. We discuss a genuine example within the context of storage ring-free electron laser physics, by presenting a model which allows the characterization of the system evolution and the determination of the conditions leading to the suppression of instabilities of sawtooth type. The conclusions of the model are confirmed by a comparison with experimental results on the Super Aco Storage Ring-Free Electron Laser.

We consider a free-electron laser (FEL) operating in the high-gain regime including the mechanism of self-induced harmonic generation (SIHG). We discuss the mechanism leading to saturation at these higher harmonics and analyze the effect of beam quality variations. Finally, we study an undulator configuration that allows the saturated harmonic power to become comparable with that of the fundamental.

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.