M. Migliorati

Electron Linac design to drive bright Compton back-scattering gamma-ray sources

The technological development in the field of high brightness linear accelerators and high energy/high quality lasers enables today designing high brilliance Compton-X and Gamma-photon beams suitable for a wide range of applications in the innovative field of nuclear photonics. The challenging requirements of this kind of source comprise: tunable energy (1–20 MeV), very narrow bandwidth (0.3%), and high spectral density (104 photons/s/eV). We present here a study focused on the design and the optimization of an electron Linac aimed to meet the source specifications of the European Extreme Light Infrastructure—Nuclear Physics project, currently funded and seeking for an innovative machine design in order to outperform state-of-the-art facilities. We show that the phase space density of the electron beam, at the collision point against the laser pulse, is the main quality factor characterizing the Linac.

Laser-driven electron beamlines generated by coupling laser-plasma sources with conventional transport systems

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.

Sheffer polynomials, monomiality principle, algebraic methods and the theory of classical polynomials

The Sheffer polynomials and the monomiality principle, along with the underlying operational formalism, offer a powerful tool for investigation of the properties of a wide class of polynomials. We present, within such a context, a self-contained theory of such familiar systems of polynomials as the Euler, Bernoulli, Bessel and other clasical polynomials and show how the derivation of some of their old and new properties is greatly simplified.

A compact post-acceleration scheme for laser-generated protons

Protons generated by irradiating a thin metal foil with a high-intensitylaser have shown to posses interesting characteristics in terms of energy, emittance, current, and pulse duration. Therefore, in the near future, they might become a competitive source with respect to conventional proton sources. Previous theoretical, numerical, and experimental studies have already demonstrated efficient coupling between laser-accelerated proton beams with traditional radio frequency (RF)-based particle accelerators. These hybrid proton accelerators benefit from both the excellent properties of the laser-based source and the flexibility, reliability, and know-how of beam handling as provided by RF-based accelerator structures. In this paper, state of the art experimental results of laser-accelerated proton beams are used as input for a numerical study using compact and innovative conventional accelerator structures designed for medical applications. Results show that this compact hybrid accelerator allows even more efficient capture and acceleration of the laser-generated proton beam.

The Project Plasmonx for Plasma Acceleration Experiments and A Thomson X-Ray Source at SPARC

We present the status of the project PLASMONX, recently approved by INFN. This project, based on a collaboration between INFN and CNR-IPCF, aims at a long term upgrade of the SPARC system with the goal to develop at LNF an integrated facility for advanced beam-laser-plasma research in the field of advanced acceleration techniques and ultra-bright X-ray radiation sources and related applications. The project, in its first phase, foresees the development at LNF of a High Intensity Laser Laboratory (HILL) whose main component is a 100 TW-class Ti: Sa laser system synchronized to the SPARC photo-injector. Experiments of self-injection and acceleration of electrons into laser driven plasma waves will be conducted at HILL-LNF, early in this first project phase. Eventually an additional beam line will be built in the SPARC bunker in order to transport the SPARC electron beam at an interaction point, where a final focus system will allow to conduct experiments either of laser-beam co-propagation in plasma waves for high gradient acceleration, or experiments of laser-beam head-on collisions to develop a Thomson source of bright ultra-short X-ray radiation pulses, with X-ray energies tunable in the range 20 to 1000 keV and pulse duration from 30 fs to 20 ps. Preliminary simulations of plasma acceleration with self-injection are illustrated, as well as external injection of the SPARC electron beam.

Electron beam properties and impedance characterization for storage rings used for free electron lasers

Abstract Good electron beam qualities and stability are the crucial features of Storage Rings dedicated to synchrotron radiation sources or to Free Electron Laser. Most of these characteristics depend on the coupling of the e-beam with the machine environment, which can be in turn modelled in terms of a characteristic impedance, whose absolute value and structure can be used to specify both the stability (longitudinal and transverse) of the beam and its qualities (energy spread, bunch length, peak current, etc.). In this paper we consider two specific examples of Storage Rings used for FEL operation and analyze their performances by means of semianalytical and numerical methods. The analysis is aimed at clarifying the dependence of beam energy spread and bunch length on beam current and at providing a set of parameters useful for the optimization of Free Electron Laser or synchrotron radiation sources.

The SPARC/X SASE-FEL Projects

SPARC and SPARX are two different initiatives toward an Italian Free Electron Laser ~FEL! source operating in the Self Amplified Spontaneous Emission ~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.

Beam dynamics studies for the SPARC project

The aim of the SPARC project, is to promote an R&D activity oriented to the development of a high brightness photoinjector to drive SASE-FEL experiments. We discuss in this paper the status of the beam dynamics simulation activities.

Saw-tooth instability in storage rings: simulations and dynamical model

Abstract The saw-tooth instability in storage rings is studied by means of a time-domain simulation code which takes into account the self-induced wake fields. The results are compared with those from a dynamical heuristic model exploiting two coupled non-linear differential equations, accounting for the time behavior of the instability growth rate and for the anomalous growth of the energy spread. This model is shown to reproduce the characteristic features of the instability in a fairly satisfactory way.

EMITTANCE DEGRADATION DUE TO WAKE FIELDS IN A HIGH BRIGHTNESS PHOTOINJECTOR

Wake fields effects in addition to space charge forces may have an important impact during the emittance compensation process in a high brightness photo-injector. To study this effect we developed an upgraded version of the Homdyn code including off axis beam dynamics and wake fields. Homdyn describes a bunch as a uniformly charged cylinder, divided in cylindrical slices; in the upgraded version each slices centroid can be transversally displaced from the nominal axis thus inducing wake fields. When the bunch is short as compared to the beam pipe radius, wake fields for a single cavity are calculated using methods of diffraction theory; instead we use, for a periodic collection of cavities, an asymptotic wake field obtained numerically at SLAC and then fitted to a simple function. As a first application we studied and verified a correction scheme for the SPARC photo-injector to control the bunch trajectory and angle at the entrance of the undulator. The correction scheme consists of a number of steering ...