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We present the design of a photon-photon collider based on conventional Compton gamma sources for the observation of elastic $\ensuremath{\gamma}\ensuremath{\gamma}$ scattering. Two symmetric electron beams, generated by photocathodes and accelerated in linacs, produce two primary gamma rays through Compton backscattering with two high energy lasers. The elastic photon-photon scattering is analyzed by start-to-end simulations from the photocathodes to the detector. A new Monte Carlo code has been developed ad hoc for the counting of the QED events. Realistic numbers of the secondary gamma yield, obtained by using the parameters of existing or approved Compton devices, a discussion of the feasibility of the experiment and of the nature of the background are presented.

In a recent paper [14] , a scheme for inserting and extracting high brightness electron beams to/from a plasma based acceleration stage was presented and proved to be effective with an ideal bi-Gaussian beam, as could be delivered by a conventional photo-injector. In this paper, we extend that study, assessing the method stability against some jitters in the properties of the injected beam. We find that the effects of jitters in Twiss parameters are not symmetric in results; we find a promising configuration that yields better performances than the setting proposed in [14] . Moreover we show and interpret what happens when the beam charge profiles are modified.

The aim of this work is to examine a few aspects of Jacques Derrida’s reading of the philosophy of Heidegger and Levinas. Specifically, we intend to show that the criticism Derrida directs towards certain themes in Levinas’s thought at the same time contains a revaluation of Heidegger’s ontology as it was developed during the 1920s, before the so-called Kehre. What this triple hermeneutic comparison puts into play is the relationship between ethics and ontology. In critiquing the relationship between these two concepts in Levinas, Derrida seems to move closer to the way they are described and developed in both Being and Time and in Kant and the Problem of Metaphysics. Finally, we will try to show how this reevaluation of ontology by Derrida determines his approach to the philosophy of Jean-Luc Nancy, whose ethics, differently from Levinas’s, is an ethics of ontology.

The SPARC_LAB Thomson source is a compact X-ray source based on the Thomson backscattering process presently under its second phase of commissioning at the LNF. The electron beam energy ranges between 30 and 150 MeV, the electrons collide head-on with the Ti:Sapphire FLAME laser pulse the energy of which ranges between 1 and 5 J with pulse lengths in the 25 fs–10 ps range, this provides an X-ray energy tunability in the range of 20–500 keV, with the further capability to generate strongly non-linear phenomena and to drive diffusion processes due to multiple and plural scattering effects. The experimental results of the obtained X-ray radiation are presented.

A systematic study of the polarization of x-gamma rays produced in Thomson and Compton scattering is presented, in both classical and quantum schemes. Numerical results and analytical considerations let us to establish the polarization level as a function of acceptance, bandwidth and energy. Few sources have been considered: the SPARC_LAB Thomson device, as an example of a x-ray Thomson source, ELI-NP, operating in the gamma range. Then, the typical parameters of a beam produced by a plasma accelerator has been analyzed. In the first case, with bandwidths up to 10%, a contained reduction ($l10%$) in the average polarization occurs. In the last case, for the nominal ELI-NP relative bandwidth of $5\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}3}$, the polarization is always close to 1. For applications requiring larger bandwidth, however, a degradation of the polarization up to 30% must be taken into account. In addition, an all optical gamma source based on a plasma accelerated electron beam cannot guarantee narrow bandwidth and high polarization operational conditions required in nuclear photonics experiments.

A new technique, named “laser comb”, was tested during the last SPARC run. It is able to produce electron pulse trains with a charge of some hundreds pC, a repetition rate of some terahertz, and a sub-picosecond length. This technique is based on the velocity bunching configuration of the SPARC injector. It can be useful to drive pump and probe free-electron laser experiments, to generate coherent excitation of plasma waves in plasma accelerators, and to produce narrow band terahertz radiation. In this paper, we describe the experimental results achieved so far and provide a comparison with simulations.

A 250-TW laser system (FLAME - Frascati laser for acceleration and multidisciplinary experiments) is now in its commissioning phase in a new laboratory at LNF-INFN in the framework of the PLASMONX (Plasma acceleration and monochromatic X-ray generation) project. The laser will deliver < 25 fs duration pulses with an energy up to 6J, at a 10Hz repetition rate. An ad hoc target area has also been designed and is currently being set up, allowing the first test experiments of electron laser wakefield acceleration to be carried out over the next few months in a safe, radiation-protected environment. An overview of the main features of the laser system and target area is given, along with a survey of the design and set-up of the self-injection test experiment, which is expected to reach the production of sub-GeV electron bunches. © 2010 Taylor and Francis.

A new laser chirping prescription is derived by means of the phase-stationary method for an incident Gaussian laser pulse in conjunction with a Lienard-Wiechert calculation of the scattered radiation flux and spectral brilliance. This particularly efficient laser chirp has been obtained using the electric field of the laser and for electrons and radiation on axis. The frequency modulation is somewhat reduced with respect to that proposed in the previous literature, allowing the application of this procedure to lasers with larger values of the parameter a0. Numerical calculations have been performed using mildly focused and narrow bandwidth laser pulses, confirming a larger efficiency of the chirp prescription here introduced. The chirp efficiency has been analysed as a function of the laser parameter and focusing.A new laser chirping prescription is derived by means of the phase-stationary method for an incident Gaussian laser pulse in conjunction with a Lienard-Wiechert calculation of the scattered radiation flux and spectral brilliance. This particularly efficient laser chirp has been obtained using the electric field of the laser and for electrons and radiation on axis. The frequency modulation is somewhat reduced with respect to that proposed in the previous literature, allowing the application of this procedure to lasers with larger values of the parameter a0. Numerical calculations have been performed using mildly focused and narrow bandwidth laser pulses, confirming a larger efficiency of the chirp prescription here introduced. The chirp efficiency has been analysed as a function of the laser parameter and focusing.

Purpose The development of compact sources of high brilliance, mono-chromatic, tunable X-rays with energy in the range 30–150 keV is a topical research field; applications in radiodiagnostics are foreseen. The aim of this work is to propose the use of a compact source based on X-ray Compton back-scattering (also known as Inverse Compton Source, ICS) developed within the MariX/BriXS project [1] , for kilovoltage rotational radiotherapy dedicated to the breast. Methods The proposed source is based on a modified Tigner scheme of push-and-pull twin Super-Conducting Energy Recovery Linacs, just wrapped on itself in order to halve the overall length of the machine. The ICS source was simulated by using the code CAIN and the output X-ray photon beam was obtained. The anticipated performances are a flux up to 1013 photons/s within 5% bandwidth, coming in radiation pulses a few psec long at a repetition rate up to 100 MHz, fully tunable in the 20–150 keV energy range with full control of polarization and adjustable bandwidth in the range 0.5–10%. The simulated X-ray spectrum was used as an input of a previously validated Monte Carlo Geant4 code to calculate the dose distribution in a 50/50 breast phantom during a rotational radiotherapy scan. The pendant breast was modelled as a cylinder of 14 cm diameter and 9 cm height irradiated over 360 deg at 88 keV average energy and a 1-cm tumor was simulated at the isocenter. Results The dose distribution obtained with the kilovoltage beam generated by the ICS source shows that it is possible to perform a partial breast irradiation with dose levels to the target and to the skin, compatible with clinical treatments using conventional linacs. Conclusions We proposed the application of a Compton back-scattering X-ray source for kilovoltage rotational radiotherapy for breast cancer. The technique could be useful for partial breast irradiation with or without injection of a dose enhancement agent, for radiosurgery of small size breast tumors.

In this paper we discuss recent results in the design configuration and modelling of the PLASMON-X project aimed at the development of an innovative, high-gradient acceleration with super-intense and ultra-short laser pulses, and a tuneable, hard X/γ-ray source, based upon Thomson scattering of optical photons by energetic electrons. Both experiments require very high power, ultra-short laser pulses in combination with very bright and short electron bunches generated either by conventional acceleration (LINAC) or by laser-driven, self injection acceleration in plasmas. The main issues concerning the integrated use of unique laser and linear accelerator installations, and the complementary use of all-optical configurations will be briefly examined.

The interaction between a very high-brightness electron beam and a relativistically intense optical laser pulse produces X-rays via coherent Thomson back scattering with FEL collective amplification. The phenomenon is, however, very selective, so that the characteristics of both electron and laser beam must satisfy tight requirements in terms of beam current, emittance, energy spread and laser amplitude stability within the pulse. The three-dimensional equations governing the radiation phenomena have been studied in both linear and non-linear regime and solved numerically for the particularly interesting values of wavelengths of 1 A, 1 and 12 nm. The performance of the collective Thomson source has been compared with that of an equivalent static undulator. A set of scaling laws ruling the phenomenon is also presented.

We present the architecture and some applications of a genetic algorithm developed for solving problems in beam dynamics of high brightness beams, where highly non-linear behaviour of the beam characteristics are optimized through a multi-dimensional variation technique based on genetic evolution criteria.

A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation of quasi-monoenergetic GeV-electrons. With future Petawatt lasers ultra-high beam currents of ~100 kA in ~10 fs can be expected, allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a table-top X-ray-FEL which may open a brilliant light source also for new ways in clinical diagnostics., Comment: 6 pages, 4 figures; accepted for publication in Appl. Phys. B

A 3-dimensional time-domain simulation of X-ray produced by a laser wakefield accelerated electron beam was performed in order to know its properties like intensity, spectrum, divergence and coherence. Particular attention was paid to the coherence around the acceleration axis. The broad spectrum of betatron radiation (1–10 keV) leads to a short coherence length. Nevertheless we observe that under particular detection condition the spatial coherence has a characteristic enlargement. We give a simplified interpretation of this effect in terms of phase shift of the electric field on a virtual detector. Moreover we describe a near field scattering technique to characterize the betatron radiation. This diagnostics will be used to map the transverse spatio-temporal coherence of X-ray radiation in the laser wakefield accelerator under development at Frascati National Laboratories (LNF).

Collective effects in the radiation emission via Thomson back-scattering of an intense optical laser pulse by high brightness electron beams are analyzed. The micro-bunching of the electron beam on the scale of the wavelength of the emitted radiation and the consequent free-electron-laser instability may significantly enhance the number of photons emitted. Scaling-laws of the radiation properties, both in the collective and incoherent spontaneous regimes versus laser and electron beam parameters are discussed in the framework of the one-dimensional model.

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.

In this paper we resurrect an idea originally proposed by Serafini[1] in 1992 for an RF photocathode gun capable of operating simultaneously at the fundamental frequency and a higher frequency harmonic. Driving the gun at two frequencies with the proper field ratio and relative phase produces a beam with essentially no rf emittance and a linear longitudinal phase space distribution. Such a gun allows a completely new range of operating parameters for controlling space charge emittance growth. In addition, the linear longitudinal phase space distribution aids in bunch compression. This paper will compare results of simulations for the two-frequency gun with the standard rf gun, and the unique properties of the two-frequency gun will be discussed.

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 design of the Linac Coherent Light Source assumes that a low-emittance, 1-nC, 10-ps beam will be available for injection into the 15-GeV linac. The proposed rf photocathode injector that will provide a 150-MeV beam with rms normalized emittances of 1 mm in both the transverse and longitudinal dimensions is based on a 1.6-cell S-band rf gun that is equipped with an emittance compensating solenoid. The booster accelerator is positioned at the beam waist coinciding with the first emittance maximum and is provided with an accelerating gradient of ~25 MeV/m, i.e., the "new working point." The uv pulses required for cathode excitation will be generated by tripling the output of a Ti:sapphire laser system consisting of a highly stable cw mode-locked oscillator and two bow-tie amplifiers pumped by a pair of Q-switched Nd:YAG lasers. The large bandwidth of the Ti:sapphire system accommodates the desired temporal pulse shaping. Details of the design and the supporting simulations are presented., Comment: 13 pages (double spaced), 4 figures, contributed to The 23rd International Free Electron Laser Conference, Darmstadt, Germany, 20-24 August 2001

We present a simple and new scheme for producing two-colour Thomson/Compton radiation with the possibility of controlling separately the polarization of the two different colours, based on the interaction of one single electron beam with two light pulses that can come from the same laser setup or from two different lasers and that collide with the electrons at different angle. One of the most interesting cases for medical applications is to provide two X-ray pulses across the iodine K -edge at 33.2 keV. The iodine is used as contrast medium in various imaging techniques and the availability of two spectral lines accross the K -edge allows one to produce subtraction images with a great increase in accuracy.

The two-dimensional single shot transverse coherence of the Self-Amplified Spontaneous Emission of the SPARC-LAB Free-Electron Laser was measured through the statistical analysis of a speckle field produced by heterodyning the radiation beam with a huge number of reference waves, scattered by a suspension of particles. In this paper we report the measurements and the evaluation of the transverse coherence along the SPARC-LAB undulator modules. The measure method was demonstrated to be precise and robust, it does not require any a priori assumptions and can be implemented over a wide range of wavelengths, from the optical radiation to the x-rays.

At the SPARC_LAB facility of INFN-LNF we are installing two transport lines for ultra-short electron bunches and an ultra- intense laser pulses, generated by the SPARC photo-injector and by the FLAME laser in a synchronized fashion at the tens of f s level, to co-propagate inside a hydrogen filled glass capillary, in order to perform acceleration of the electron bunch by a plasma wave driven by the laser pulse. The main aim of this experiment is to demonstrate that a high brightness electron beam can be accelerated by a plasma wave without any significant degradation of its quality. Motivations of the technical choices made and expected performances are reported.

A new kind of nonresonant optical recirculator, dedicated to the production of $\ensuremath{\gamma}$ rays by means of Compton backscattering, is described. This novel instrument, inspired by optical multipass systems, has its design focused on high flux and very small spectral bandwidth of the $\ensuremath{\gamma}$-ray beam. It has been developed to fulfill the project specifications of the European Extreme Light Infrastructure ``Nuclear Pillar,'' i.e., the Gamma Beam System. Our system allows a single high power laser pulse to recirculate 32 times synchronized on the radio frequency driving accelerating cavities for the electron beam. Namely, the polarization of the laser beam and crossing angle between laser and electrons are preserved all along the 32 passes. Moreover, optical aberrations are kept at a negligible level. The general tools developed for designing, optimizing, and aligning the system are described. A detailed simulation demonstrates the high efficiency of the device.

This paper describes the scientific aims and potentials as well as the preliminary technical design of RUDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity "particles factory", based on a combination of high duty cycle radio-frequency superconducting electron linacs and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. [RIDE is also supposed to be realized in subsequent stages of development depending on the assigned priorities. (C) 2013 Elsevier B.V. All rights reserved.

We report on the design of the rf photoinjector of the Linac Coherent Light Source (LCLS). The rf photoinjector is required to produce a single 150 MeV bunch of {approximately}1 nC and {approximately}100 A peak current at a repetition rate of 120 Hz with a normalized rms transverse emittance of {approximately}1 {pi} mm-mrad. The design employs a 1.6-cell S-band rf gun with an optical spot size at the cathode of a radius of {approximately}1 mm and a pulse duration with an rms sigma of {approximately}3 ps. The peak rf field at the cathode is 150 MV/m with extraction 57 {degree} ahead of the rf peak. A solenoidal field near the cathode allows the compensation of the initial emittance growth by the end of the injection linac. Spatial and temporal shaping of the laser pulse striking the cathode will reduce the compensated emittance even further. Also, to minimize the contribution of the thermal emittance from the cathode surface, while at the same time optimizing the quantum efficiency (QE), the laser wavelength for a Cu cathode should be tunable around 260 nm. Following the injection linac the geometric emittance simply damps linearly with energy growth. PARMELA simulations show that this design willmore » produce the desired normalized emittance, which is about a factor of two lower than has been achieved to date in other systems. In addition to low emittance, we also aim for laser amplitude stability 1% in the UV and a timing jitter in the electron beam of 0.5 ps rms, which will lead to less than 10% beam intensity fluctuation after the electron bunch is compressed in the main linac.« less

In this paper we provide an analytical description for the transverse dynamics of relativistic, space-chargedominated beams undergoing strong acceleration, such as those typically produced by rf photoinjectors. These beams are chiefly characterized by a fast transition, due to strong acceleration, from the nonrelativistic to the relativistic regime in which the initially strong collective plasma effects are greatly diminished. However, plasma oscillations in the transverse plane are still effective in significantly perturbing the evolution of the transverse phase space distribution, introducing distortions and longitudinal-transverse correlations that cause an increase in the rms transverse emittance of the beam as a whole. The beam envelope evolution is dominated by such effects and not by the thermal emittance, and so the beam flow can be considered quasilaminar. The model adopted is based on the rms envelope equation, for which we find an exact particular analytical solution taking into account the effects of linear space-charge forces, external focusing due to applied as well as ponderomotive RF forces, acceleration, and adiabatic damping, in the limit that the weak nonlaminarity due to the thermal emittance may be neglected. This solution represents a special mode for beam propagation that assures a secularly diminishing normalized rms emittance and it represents the fundamental operating condition of a space-charge-compensated RF photoinjector. The conditions for obtaining emittance compensation in a long, integrated photoinjector, in which the gun and linac sections are joined, as well as in the case of a short gun followed by a drift and a booster linac, are examined. @S1063-651X~97!10706-1#

In December 2010 the Basel Committee on Banking Supervision published a set of new regulations for banks in response to the financial crisis. This paper aims at evaluating the possible effects of the new framework on banks� available regulatory capital and risk-weighted assets and assessing their positioning with respect to future leverage and liquidity constraints. The evidence, based on the data collected from a representative sample of 13 Italian banking groups updated to 30 June 2012, show that capital and liquidity positions relatively to the Basel 3 targets have improved considerably over the last two years. Furthermore, compared to banks in other jurisdictions, Italian intermediaries are likely to be less affected by the reform, due to a business model more focused on credit intermediation. Importantly, the estimates cannot be interpreted as a forecast of capital and liquidity needs as they do not incorporate any assumption about future balance-sheet items or banks� reactions to the changing regulatory and economic environment.

We analyze the nonlinear classical effects of the $\mathrm{X}/\ensuremath{\gamma}$ radiation produced by Thomson/Compton sources. We confirm the development of spectral fringes of the radiation on axis, which comports broadening, shift, and deformation of the spectrum. For the nominal parameters of the SPARC-LAB Thomson scattering and of the European Proposal for the gamma source ELI-NP, however, the radiation, when collected in the suitable acceptance angle, does not reveal many differences from that predicted by the linear model and the nonlinear redshift is subdominant with respect to the quantum recoil. An experiment aimed to the study of the nonlinearities is proposed on the SPARC-LAB source.

Laser-based electron sources are attracting strong interest from the conventional accelerator community due to their unique characteristics in terms of high initial energy, low emittance, and significant beam current. Extremely strong electric fields (up to hundreds of $\mathrm{GV}/\mathrm{m}$) generated in the plasma allow accelerating gradients much higher than in conventional accelerators and set the basis for achieving very high final energies in a compact space. Generating laser-driven high-energy electron beam lines therefore represents an attractive challenge for novel particle accelerators. In this paper we show that laser-driven electrons generated by the nowadays consolidated TW laser systems, when leaving the interaction region, are subject to a very strong, normalized emittance worsening which makes them quickly unusable for any beam transport. Furthermore, due to their intrinsic beam characteristics, controlling and capturing the full beam current can only be achieved improving the source parameters.

Nuclear instruments & methods in physics research / A 720, 153 - 156 (2013). doi:10.1016/j.nima.2012.12.012, Published by North-Holland Publ. Co., Amsterdam

We analyze the energy distribution of a relativistic electron beam after the Compton back-scattering by a counterpropagating laser field. The analysis is performed for parameters in the range of realistic X-γ sources, in the framework of the Quantum Electrodynamics, by means of the code CAIN. The results lead to the conclusion that, in the regime considered, the main effect is the initial formation of stripes, followed by the diffusion of the most energetic particles toward lower values in the longitudinal phase space, with a final increase of the electron energy bandwidth. © Copyright EPLA, 2013.

A new facility named SPARC-LAB has been recently launched at the INFN National Laboratories in Frascati, merging the potentialities of the former projects SPARC and PLASMONX. We describe in this paper the status and the future perspectives at the SPARC-LAB facility. © 2013 Elsevier B.V. All rights reserved.

In this manuscript we review the challenges of Compton backscattering sources in advancing photon beam performances in the 1 – 20 MeV energy range, underlining the design criteria bringing to maximum spectral luminosity and briefly describing the main achievements in conceiving and developing new devices (multi-bunch RF cavities and Laser recirculators) for the case of ELI-NP Gamma Beam System (ELI-NP-GBS).

We discuss an example of a free electron laser dedicated to the triggering of a photocathode gun. The advantages offered by such a solution with respect to conventional systems are analyzed.

Laser-driven electron beamlines are receiving increasing interest from the particle accelerator community. In particular, the high initial energy, low emittance, and high beam current of the plasma based electron source potentially allow generating much more compact and bright particle accelerators than what conventional accelerator technology can achieve. Using laser-generated particles as injectors for generating beamlines could significantly reduce the size and cost of accelerator facilities. Unfortunately, several features of laser-based particle beams need still to be improved before considering them for particle beamlines and thus enable the use of plasma-driven accelerators for the multiple applications of traditional accelerators. Besides working on the plasma source itself, a promising approach to shape the laser-generated beams is coupling them with conventional accelerator elements in order to benefit from both a versatile electron source and a controllable beam. In this paper, we perform start-to-end simulations to generate laser-driven beamlines using conventional accelerator codes and methodologies. Starting with laser-generated electrons that can be obtained with established multi-hundred TW laser systems, we compare different options to capture and transport the beams. This is performed with the aim of providing beamlines suitable for potential applications, such as free electron lasers. In our approach, we have analyzed which parameters are critical at the source and from there evaluated different ways to overcome these issues using conventional accelerator elements and methods. We show that electron driven beamlines are potentially feasible, but exploiting their full potential requires extensive improvement of the source parameters or innovative technological devices for their transport and capture.

In this paper we discuss the design of a possible superconducting photoinjector able to produce long pulses of high charge electron bunches, as required for the TESLA project. An extrapolation to high brightness cw electron beams for inertial fusion and X-UV FEL experiments is also given, together with an analysis of the R&D needed for the actual injector development. The requirements for the photocathode which has to deliver high current density in a SC environment are discussed on the basis of the preliminary results of the Wuppertal experiment, performed in the context of an international collaboration.

The behavior of single particle beam dynamics in long rf guns is discussed, mainly concerning the effect of rf focusing, relevant in a high gradient standing wave structure. An analytical transport matrix is derived and compared to simulations, showing that it is possible to transport the beam through the gun up to full scale injector energy (1 GeV) without the need for any other external focusing.

In this paper we present a general review of beam dynamics in a laser-driven rf gun. The peculiarity of such an accelerating structure versus other conventional multi-cell linac structures is underlined on the basis of the Panofsky-Wenzel theorem, which is found to give a theoretical background for the well known Kim's model. A basic explanation for some proposed methods to correct rf induced emittance growth is also derived from the theorem. We also present three emittance correction techniques for the recovery of space-charge induced emittance growth, namely the optimum distributed disk-like bunch technique, the use of rf spatial harmonics to correct spherical aberration induced by space charge forces and the technique of emittance filtering by clipping the electron beam. The expected performances regarding the beam quality achievable with different techniques, as predicted by scaling laws and simulations, are analyzed, and, where available, compared to experimental results.

Peak current represents a key demand for new generation electron beam photoinjectors. Many beam applications, such as free electron laser, inverse Compton scattering, terahertz radiation generation, have efficiencies strongly dependent on the bunch length and current. A method of beam longitudinal compression (called velocity bunching) has been proposed some years ago, based on beam longitudinal phase space rotation in a rf field potential. The control of such rotation can lead to a compression factor in excess of 10, depending on the initial longitudinal emittance. Code simulations have shown the possibility to fully compensate the transverse emittance growth during rf compression, and this regime has been experimentally proven recently at SPARC. The key point is the control of transverse beam plasma oscillations, in order to freeze the emittance at its lowest value at the end of compression. Longitudinal and transverse phase space distortions have been observed during the experiments, leading to asymmetric current profiles and higher final projected emittances. In this paper we discuss in detail the results obtained at SPARC in the regime of velocity bunching, analyzing such nonlinearities and identifying the causes. The beam degradation is discussed, both for slice and projected parameters. Analytical tools are derived to experimentally quantify the effect of such distortions on the projected emittance.

The advance in laser-plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular, the upcoming experiments with the 250 TW laser at the FLAME facility of the INFN Laboratori Nazionali di Frascati, will enter the GeV regime with more than 100 pC of electrons. At the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need for developing a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV), with still unknown angular divergences. Within the PlasmonX experiment at FLAME, a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence, present challenges in the design and construction of such a device. We present the design considerations for this spectrometer that lead to the use of scintillating fibers, multichannel photo-multipliers and a multiplexing electronics, a combination which is innovative in the field. We also present the experimental results obtained with a high intensity electron beam performed on a prototype at the LNF beam test facility. (C) 2011 Elsevier B.V. All rights reserved.

In this Letter we report the first experiments aimed at the simultaneous demonstration of the emittance compensation process and velocity bunching in a high brightness electron source, the SPARC photoinjector in INFN-LNF. While a maximum compression ratio up to a factor 14 has been observed, in a particular case of interest a compression factor of 3, yielding a slice current of 120 A with less than 2 microm slice emittance, has been measured. This technique may be crucial in achieving high brightness beams in photoinjectors aiming at optimized performance of short wavelength single-pass free electron lasers or other advanced applications in laser-plasma accelerators.

Thomson scattering X-ray sources have many features which are of relevance for several applications: the main one is the capability to produce intense, quasi-monochromatic, tunable X-ray beams, after collimation, still with a reasonably small size apparatus. Applications to medical physics are straightforward, in particular in mammography where dose control in screening programs is the main relevant issue. An optimal choice of the X-ray energy to image the breast will result in a best image quality and hence will lead to a dose reduction. A Thomson scattering source is presently under development at the Frascati National Laboratories (LNF) of INFN (Istituto Nazionale di Fisica Nucleare). A complete simulation of the source including electron beam, laser beam, Thomson interaction and X-ray imaging is presented. The X-rays are generated in the energy range suitable for mammography and used to generate images of a mammographic phantom. Image quality is evaluated in terms of dose efficiency and compared to those obtained by monochromatic beams and conventional X-ray tubes.

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.

The beam dynamics in RF guns is characterized by an optimum injection phase which minimizes the RF-field-induced emittance blowup: such a condition corresponds to a vanishing first order term in the phase dependence of the exit transverse momentum. Away from the optimum phase, a sharp increase of the emittance is found. In this paper we analyze the possibility of compensating for both the first and second order terms, in order to recover the minimum emittance value even at phases different from the optimum one. Our scheme is based on the use of an unsymmetrical RF cavity, added downstream of the gun cavity and fully uncoupled from it, in order to be independently phased. At the exit of this cavity the minimum emittance value can be recovered, the injection phase being a free parameter to be independently optimized. In this way higher injection phases can be exploited, where the longitudinal rms emittance displays a minimum, and long bunches extracted from the gun can be magnetically compressed more efficiently, achieving a significant beam brightness increase with respect to conventionally optimized RF guns. An analytical study of the beam dynamics inside the unsymmetrical RF cavity is presented, together with the results of some numerical simulations performed with the PIC code ITACA [L. Serafini and C. Pagani, Proc. 1st EPAC, Rome, June 1988 (Word Scientific) p. 866].

In this paper a new method is presented to neutralize the rf-induced emittance blow-up generated inside rf electron guns. The method is based on a multi-mode operation of the rf gun cavity, which must be able to support both the accelerating mode (TM010-π) and a higher harmonic mode. The analytical study of the beam dynamics, which has been found in good agreement with the numerical simulations, shows that the growth of the normalized rms emittance, produced by the time-dependent rf forces during the acceleration in the gun, can be cancelled up to fourth-order terms. This is of great relevance for the improvement of rf gun performances, since the rf field contribution to the emittance blowup becomes negligible and no more dependent on bunch sizes, allowing in this way a natural damping also of the space charge induced emittance simply by using longer bunches, i.e., decreasing the charge density.

A form is given of the retarded electric field and magnetic induction generated by the motion of a charged particle that expresses these fields as integrals of the retarded charge density only, with kernels depending on the charge velocity and acceleration fields. In the case of a single pointlike charge, the usual Lienard-Wiechert fields follow very easily. The set of equations for the dynamics of particles in assigned electromagnetic fields with the self-consistent field is written and integrated. The code RETAR for the dynamics of charged particles in external and self-consistent fields is described and a few examples of benchmark are proposed. As a physical application, the case of an electron beam moving in a bending magnetic dipole is examined, and the radiation produced analyzed, in order to characterize a therahertz radiation source.