M. Ferrario

The SPARC project: a high-brightness electron beam source at LNF to drive a SASE-FEL experiment

Abstract The Project Sorgente Pulsata e Amplificata di Radiazione Coerente (SPARC), proposed by a collaboration among ENEA–INFN–CNR–Universita’ di Tor Vergata–INFM–ST, was recently approved by the Italian Government and will be built at LNF. The aim of the project is to promote an R&D activity oriented to the development of a coherent ultra-brilliant X-ray source in Italy. This collaboration has identified a program founded on two main issues: the generation of ultra-high peak brightness electron beams and of resonant higher harmonics in the SASE-FEL process, as presented in this paper.

Strong nonlinear terahertz response induced by Dirac surface states in Bi2Se3 topological insulator

Electrons with a linear energy/momentum dispersion are called massless Dirac electrons and represent the low-energy excitations in exotic materials such as graphene and topological insulators. Dirac electrons are characterized by notable properties such as a high mobility, a tunable density and, in topological insulators, a protection against backscattering through the spin–momentum locking mechanism. All those properties make graphene and topological insulators appealing for plasmonics applications. However, Dirac electrons are expected to present also a strong nonlinear optical behaviour. This should mirror in phenomena such as electromagnetic-induced transparency and harmonic generation. Here we demonstrate that in Bi2Se3 topological insulator, an electromagnetic-induced transparency is achieved under the application of a strong terahertz electric field. This effect, concomitantly determined by harmonic generation and charge-mobility reduction, is exclusively related to the presence of Dirac electron at the surface of Bi2Se3, and opens the road towards tunable terahertz nonlinear optical devices based on topological insulator materials.

Linear and Nonlinear Thomson Scattering for Advanced X-ray Sources in PLASMONX

Thomson scattering of laser pulses onto ultrarelativistic e-bunches is becoming an advanced source of tunable, quasi-monochromatic, and ultrashort X/gamma radiation. Sources aimed at reaching a high flux of scattered photons need to be driven by high-brightness e-beams, whereas extremely short (femtosecond scale or less) sources need to make femtosecond-long e-beams that collide with the laser pulses. In this paper, we explore the performance of the PLASMONX TS source in several operating regimes, including preliminary results on a source based on e-bunches produced by laser wakefield acceleration and controlled injection via density down ramp.

Status of Nb-Pb superconducting RF-GUN cavities

We report on the progress and status of an electron RF* gun made of two superconductors: niobium and lead [1]. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. The design of RF-gun and performance of 3 test cavities without and with the emitting lead spot are reported in this contribution. Measured quantum efficiency for lead at 2 K is presented briefly. More details are reported in [9].

Conceptual design of a high-brightness linac for soft X-ray SASE-FEL source

Abstract FELs based on SASE are believed to be powerful tools to explore the frontiers of basic sciences, from physics to chemistry to biology. Intense R&D programs have started in the USA and Europe in order to understand the SASE physics and to prove the feasibility of these sources. The allocation of considerable resources in the Italian National Research Plan (PNR) brought about the formation of a CNR–ENEA–INFN–University of Roma “Tor Vergata” study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated, leading to the SPARX proposal. We report in this paper the results of a preliminary start to end simulation concerning one option we are considering based on an S-band normal conducting linac with high-brightness photoinjector integrated in an RF compressor.

Plasma Wakefields in the Quasi‐Nonlinear Regime

It has long been noted that the nonlinear “blowout” regime of the PWFA has certain critical aspects for producing high quality beams that are owed to the elimination of electron density and current inside of the beam‐occupied region: time‐independent, linear ion‐focusing, and acceleration independent of transverse position. Unfortunately, in applying this scheme to a linear collider, efficiency considerations strongly encourage use of pulse trains, in which one superimposes the wakes of driving and accelerating beams in turn. This implies that one needs to maintain stable wakes with the ability to maintain a resonant response which, given the presence of wave‐breaking and amplitude dependent frequency, is not straightforward in the nonlinear regime. Here we propose a solution to this problem: operation in the quasi‐nonlinear regime, where one uses beams with relatively low charge and transverse beam size much smaller than a plasma skin‐depth. In this case, the beam density may exceed that of the plasma, p...

Nb-Pb Superconducting RF Gun

We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

Mapping the transverse coherence of the self amplified spontaneous emission of a free-electron laser with the heterodyne speckle method

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.

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.

Low emittance photoinjectors

Abstract Photon colliders require high charge polarized electron beams with very low normalized emittances, possibly lower than the actual damping rings design goals. Recent analytical and numerical efforts in understanding beam dynamics in RF photoinjectors have raised again the question as to whether the performances of an RF electron gun based injector could be competitive with respect to a damping ring. As a matter of discussion we report in this paper the most recent results concerning low emittance photoinjector designs: the production of polarized electron beams by DC and/or RF guns is illustrated together with space charge compensation techniques and thermal emittance effects. New ideas concerning multi-gun injection system and generation of flat beams by RF gun are also discussed.