Search

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.

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.

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.

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.

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.

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.

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 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. >

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.

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.

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 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.

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 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.

Experimental observations on FEL Storage Rings (Aco, Super-Aco, VEPP3, TERAS) have shown that in a storage ring with an operating FEL there is a mutual effect between the FEL operational mode and the beam longitudinal distribution. The main effects are the birth of a macro-temporal structure of the FEL radiation and a suppression of the synchrotron sidebands, evidence of beam stabilisation against the microwave instabilities. In this paper we discuss the main features of the beam dynamics analysed with a simulation code recently developed, which includes the FEL-beam interaction. Furtherly, we propose an heuristic model which enable to describe in a simple way the overall system.

Publisher Summary This chapter provides a simplified and heuristic approach to the free electron laser (FEL) that frames it within the context of coherent sources. The FEL is a nonconventional laser device. Powerful coherent light can be generated either by the stimulated emission of an inverted atomic or molecular medium or by free electrons moving in a waveguide or an undulator magnet. The chapter emphasizes the various effects of the dynamic behavior of the Compton FEL interaction, including the spontaneous emission, gain effects, transverse, longitudinal mode dynamics, and saturation mechanisms. The goal of the chapter is to provide simple recipes to calculate the gain when inhomogeneous broadening effects are active, or the effect of optical mode focussing induced by the interaction, and to describe the interplay between saturation and lethargy. The FEL is becoming a source of coherent radiation with the unique feature of its wide tunability.

A 5 MeV FEL facility has been realized at the ENEA Research Center in Frascati, Italy. This facility is devoted to the testing of Cerenkov FEL devices and other compact FEL configurations. Power up to 50 W in 4 microsecond(s) pulse has been generated in a Cerenkov FEL at wavelengths ranging from 0.8 to 1.6 mm using different dielectric guides. Other planned 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.

We report the observation of coherent emission from a Cherenkov free-electron laser driven by a 5-MeV radio-frequency microtron. Power up to 50 W in pulses of 4-\ensuremath{\mu}s duration has been generated at the wavelengths of 1.6 and 0.9 mm using two different dielectric-loaded waveguides.

Smith–Purcell radiation has been observed from relativistic electrons for the first time, offering the possibility of compact free-electron lasers in the far-infrared spectral region. In 1953 at Harvard, S J Smith and Edward Purcell passed 300 keV electrons over a metallic grating and observed visible radiation.

We discuss a phenomenological one-dimensional, self-consistent, multimode (longitudinal) theory for a free-electron-laser oscillator. A strong fundamental mode and a weak sideband mode are followed through many passes in the optical cavity as the energy of the electron beam decreases monotonically. The time evolution of the laser power exhibits oscillations produced by the sequential growth to saturation and subsequent decay of longitudinal modes evenly distributed in frequency.

In this work we show that the basic FEL-Cerenkov dynamics can be modelled using a pendulumlike equation in close analogy with the FEL undulator case. The analysis, including the inhomogeneous broadening effects, is worked out in the hypothesis of single-slab geometry. Two-dimensional motion dynamics effects are also included.

We discuss a phenomenological one dimensional, self-consistent, multimode (longitudinal) theory for a free electron laser oscillator. A strong fundamental mode and two weak side-band modes are followed through many passes in the optical cavity as the energy of the electron beam decreases monotonically. The time evolution of the laser power exhibits oscillations produced by the sequential growth to saturation and subsequent decay of longitudinal modes evenly distributed in frequency.

The generation of coherent synchrotron radiation using beams of relativistic electrons passed through magnetic undulators opens up tremendous scope for photochemistry in general and isotopic separation by laser in particular. Applications for plasma heating in Tokamak-type installations to trigger off the controlled nuclear fusion process are also conceivable.

The theory of the free-electron laser dynamics operating in a storage ring is reconsidered within the framework of an analytical treatment. It is pointed out that the dynamical behaviour can be characterized by the round trip evolution of self-reproducing optical field configurations (the supermodes) which allow the understanding of the laser spectral and spatial features. Simple expressions for the threshold gain and for the system efficiency are also derived.

We propose an analytical solution to the propagation equation of the optical pulse both in free-electron lasers and in optical klystrons. Our results include in a natural way the lethargy and wave-packet spreading.

The basic operating principles of far infrared Cherenkov lasers are summarized and then used as a design guide for a proposed 100 μm region oscillator experiment. A discussion of the required accelerator and resonator parameters is presented and the preliminary experimental progress is reviewed.

In the first part of this article we present a one-dimensional multimode theory of a free electron laser. We show that the evolution of the laser field in a single pass through the undulator satisfies an integral equation. The formulation is exact, describing saturation and both low and high gain regime of a long-pulse free electron laser. In the second part we derive the laser field evolution equation for an oscillator configuration in the small signal regime and the long pulse limit. The theory is based on the space-time approach that leads to a generalized Schrodinger-like equation for the laser radiation field. The explicit expressions for the solutions of the evolution equation and the gain coefficient of the system are presented; part of these results have already been derived by some of the authors using a different approach.

In this paper we attempt a preliminary comparison between FELs operating in the IR and FIR region with conventional laser sources.

In this paper we use a recently suggested analytical solution of the pulse propagation equation in free-electron lasers (FEL) to get further information on the lethargy and on the velocity of propagation of the optical packet. We also introduce a refractive index for the FEL interaction. Finally, the supermodes relevant to the regime of long electron bunch are found analytically and a comparison with earlier numerical results is carried out.

We analyze the small signal multimode aspects of the single pass free electron laser and study the operating conditions and the relevant laser parameters.

The preliminary design of an electron storage ring dedicated to the free electron laser operation, is presented. The main feature of the proposed laser is the complete tunability in the wavelength range 0.3 ?m < ? < 20 ?m with an output average power of the order of 1 kW and an efficiency, electron beam-laser beam, of ~ 2%.

The steady state features of the free electron laser amplifier operating in a storage ring is presented. The electron distribution relative to the longitudinal motion and the amplifier output are evaluated as functions of the storage ring parameters and the laser power density. It is shown that the energy transferred from the electrons to the laser beam is proportional to the energy emitted via synchrotron radiation in the whole machine.

A brief summary is given of the collaborative project between ENEA and Heriot-Watt University on the Italian ENEA free-electron laser (FEL). The importance of optical diagnostics is discussed, and an outline of the physical process of gain in a FEL is given, with special reference to phase sensitive coherent gain measurement.

We discuss the dependence of the small signal gain of an FEL upon the parameters of the electron beam of a low energy accelerating device (microtron, linac, etc.) exploited for laser operation. We emphasize the main limitation imposed by the beam brightness for both long and short wavelength operation.

A simple argument to maximize the average output laser power in a single passage FEL device is presented. The optimization parameter is the undulator number of periods. The optimum values to get both maximum gain and average power are indicated and are shown to be different.

The limitations on the FEL performances due to the electron beam length, energy spread and emittance are examined.