L. Picardi

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.

Above threshold operation of the ENEA free electron laser

Abstract Recent experimental results of the ENEA FEL experiment performed with a 20 MeV, 120 mA microtron and a linearly polarized pulsed electromagnetic undulator are reported.

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.

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.

Photoluminescence of radiation-induced color centers in lithium fluoride thin films for advanced diagnostics of proton beams

Systematic irradiation of thermally evaporated 0.8 μm thick polycrystalline lithium fluoride films on glass was performed by proton beams of 3 and 7 MeV energies, produced by a linear accelerator, in a fluence range from 1011 to 1015 protons/cm2. The visible photoluminescence spectra of radiation-induced F2 and F3+ laser active color centers, which possess almost overlapping absorption bands at about 450 nm, were measured under laser pumping at 458 nm. On the basis of simulations of the linear energy transfer with proton penetration depth in LiF, it was possible to obtain the behavior of the measured integrated photoluminescence intensity of proton irradiated LiF films as a function of the deposited dose. The photoluminescence signal is linearly dependent on the deposited dose in the interval from 103 to about 106 Gy, independently from the used proton energies. This behavior is very encouraging for the development of advanced solid state radiation detectors based on optically transparent LiF thin films f...

Numerical studies and measurements on the side-coupled drift tube linac (SCDTL) accelerating structure

Abstract The 3 GHz linac section designed for the low energy (7–65 MeV) part of TOP (therapy oncological protons) linac (Picardi et al., 1997, 1996), operating at 3 GHz frequency and in π/2 mode, consists of eight modules of the structure SCDTL (side-coupled drift tube linac). The first module is designed to accelerate 7 MeV protons up to 13.4 MeV, and a prototype is presently under construction. Electromagnetic field calculations of the non-axisymmetric cavities carried out by using MAFIA 3D code (Weiland, 1986) gave the RF wall losses and the full mode spectrum. Two prototypes, an aluminium model of the first quintuplet and a copper model of the last triplet of the module, were built in order to check the complex 3D properties of the structure, and to refine the tuning procedure. This paper reports the results of the 3D numerical simulations about the RF properties of the first module and of some RF measurements on the prototypes. The beam dynamics study results in the SCDTL section are discussed as well.

Calibration of GafChromic EBT3 for absorbed dose measurements in 5 MeV proton beam and 60Co γ-rays

PURPOSE To study EBT3 GafChromic film in low-energy protons, and for comparison purposes, in a reference (60)Co beam in order to use it as a calibrated dosimetry system in the proton irradiation facility under construction within the framework of the Oncological Therapy with Protons (TOP)-Intensity Modulated Proton Linear Accelerator for RadioTherapy (IMPLART) Project at ENEA-Frascati, Italy. METHODS EBT3 film samples were irradiated at the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Legnaro, Italy, with a 5 MeV proton beam generated by a 7 MV Van de Graaff CN accelerator. The nominal dose rates used were 2.1 Gy/min and 40 Gy/min. The delivered dose was determined by measuring the particle fluence and the energy spectrum in air with silicon surface barrier detector monitors. A preliminary study of the EBT3 film beam quality dependence in low-energy protons was conducted by passively degrading the beam energy. EBT3 films were also irradiated at ENEA-National Institute of Ionizing Radiation Metrology with gamma radiation produced by a (60)Co source characterized by an absorbed dose to water rate of 0.26 Gy/min as measured by a calibrated Farmer type ionization chamber. EBT3 film calibration curves were determined by means of a set of 40 film pieces irradiated to various doses ranging from 0.5 Gy to 30 Gy absorbed dose to water. An EPSON Expression 11000XL color scanner in transmission mode was used for film analysis. Scanner response stability, intrafilm uniformity, and interfilm reproducibility were verified. Optical absorption spectra measurements were performed on unirradiated and irradiated EBT3 films to choose the most sensitive color channel to the dose range used. RESULTS EBT3 GafChromic films show an under response up to about 33% for low-energy protons with respect to (60)Co gamma radiation, which is consistent with the linear energy transfer dependence already observed with higher energy protons, and a negligible dose-rate dependence in the 2-40 Gy/min range. Short- and long-term scanner stabilities were 0.5% and 1.5%, respectively; film uniformity and reproducibility were better than 0.5%. CONCLUSIONS The main purpose of this study was to implement EBT3 dosimetry in the proton low-energy radiobiology line of the TOP-IMPLART accelerator, having a maximum energy of 7 MeV. Low-energy proton and (60)Co calibrated sources were used to investigate the behavior of film response vs to be written in italicum dose. The calibration in 5 MeV protons is currently used for dose assessment in the radiobiological experiments at the TOP-IMPLART accelerator carried out at that energy value.

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

The Project SPARC (Sorgente Pulsata e Amplificata di Radiazione Coerente), proposed by a collaboration among ENEA-INFN-CNR-Universitadi Roma Tor Vergata- INFM-ST, was recently funded by the Italian Government. 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 (SPARX proposal (1)). The SPARC collaboration identified a program based on two main issues: the generation of ultra-high peak brightness electron beams and experimental study of SASE-FEL process with generation of resonant higher harmonics. The SPARC project is being designed in order to encompass the construction of an advanced photo- injector producing a 150-200 MeV beam to drive a SASE-FEL in the optical range. The machine will be built at LNF, inside an underground bunker: it is comprised of an rf gun driven by a Ti:Sa laser, injecting into three SLAC accelerating sections. We foresee conducting investigations on the emittance correction(2) and on the rf compression techniques(3), which are expected to increase the peak current achievable at the injector exit up to kA level, with proper preservation of the transverse emittance. Although the system is expected to drive a FEL experiment, it can be used also to investigate beam physics issues like surface-roughness-induced wake fields, bunch-length measurements in the sub-ps range, emittance degradation in magnetic compressors due to CSR, and Compton backscattering production of sub-ps X-ray pulses.

The TOP project status

ENEA, in collaboration with ISS (Italian National Institute of Health), is developing a dedicated proton medical accelerator. The TOP (Oncological Therapy with Protons) linac is to be installed at the IFO Oncological Hospital in Rome. It will be a sequence of three pulsed (5 psec, 300 Hz) linear accelerators: a 7 MeV, 425 MHz RFQ+DTL (AccSys Model PL-7), a 7-65 MeV, 2998 MHz Side Coupled Drift Tube Linac (SCDTL) and a 65-200 MeV, variable energy 2998 MHz Side Coupled Linac (SCL). The 7 MeV injector output will also be used in high current mode for F-18 radioisotope production. The SCDTL output will be used for proton treatment of ocular melanoma and for radiobiology studies, with the SCL output dedicated to proton treatment of deep seated tumours. The 7 MeV injector has been completed by AccSys and shipped to ENEA in Frascati and the first SCDTL module (to boost the beam from 7 to 13.4 MeV) has been constructed. The low energy (7 MeV) beam lines for F-18 production and injection in the SCDTL are under construction. The characteristics of the various accelerator components and the status of the project are presented.

Electron accelerators at the ENEA center at Frascati: Development and application

Abstract At the ENEA Frascati Center a number of electron accelerators have been constructed with the aim of their application in scientific research (free-electron lasers, neutron spectroscopy) and industrial materials treatment (cross-linking of polymers, detoxification of potable waters, degradation of phenols). A description of the machines and their application results is given.