Mariapompea Cutroneo

Thomson parabola spectrometry for gold laser-generated plasmas

The plasma generated from thin gold films irradiated in high vacuum at high intensity (∼1015 W/cm2) laser shot is characterized in terms of ion generation through time-of-flight techniques and Thomson parabola spectrometry. Gold ions and protons, accelerated in forward direction by the electric field developed in non-equilibrium plasma, have been investigated. Measurements, performed at PALS laboratory, give information about the gold charge states distributions, the ion energy distributions and the proton acceleration driven as a function of film thickness, laser parameters, and angular emission. The ion diagnostics of produced plasma in forward direction permits to understand some mechanisms developed during its expansion kinetics. The role of the focal position of a laser beam with respect to the target surface, plasma properties, and the possibility to accelerate protons up to energies above 3 MeV has been presented and discussed.

ELIMED, MEDical and multidisciplinary applications at ELI-Beamlines

ELI-Beamlines is one of the pillars of the pan-European project ELI (Extreme Light Infrastructure). It will be an ultra high-intensity, high repetition-rate, femtosecond laser facility whose main goal is generation and applications of high-brightness X-ray sources and accelerated charged particles in different fields. Particular care will be devoted to the potential applicability of laser-driven ion beams for medical treatments of tumors. Indeed, such kind of beams show very interesting peculiarities and, moreover, laser-driven based accelerators can really represent a competitive alternative to conventional machines since they are expected to be more compact in size and less expensive. The ELIMED project was launched thanks to a collaboration established between FZU-ASCR (ELI-Beamlines) and INFN-LNS researchers. Several European institutes have already shown a great interest in the project aiming to explore the possibility to use laser-driven ion (mostly proton) beams for several applications with a particular regard for medical ones. To reach the project goal several tasks need to be fulfilled, starting from the optimization of laser-target interaction to dosimetric studies at the irradiation point at the end of a proper designed transport beam-line. Researchers from LNS have already developed and successfully tested a high-dispersive power Thomson Parabola Spectrometer, which is the first prototype of a more performing device to be used within the ELIMED project. Also a Magnetic Selection System able to produce a small pencil beam out of a wide energy distribution of ions produced in laser-target interaction has been realized and some preliminary work for its testing and characterization is in progress. In this contribution the status of the project will be reported together with a short description of the of the features of device recently developed.

TNSA ion acceleration at 1016 W/cm2 sub-nanosecond laser intensity

Micrometric thin targets have been irradiated in vacuum in TNSA (Target Normal Sheath Acceleration) configuration at PALS Laboratory in Prague by using 1016 W/cm2 laser intensity, 1315 nm wavelength, 300 ps pulse duration and different laser beam energies and focal positions. The plasmas produced were characterized by using ion collectors, semiconductor SiC detectors, X-ray streak camera and Thomson parabola spectrometer. Time of flight techniques, time resolved imaging and ion deflection spectrometry were used to characterize the laser-generated non-equilibrium plasma and the electric field driving ion acceleration developed at the rear side of the target. The maximum ion acceleration can be obtained for optimal film thickness depending on the laser energy and on the kind of irradiated targets. Special targets containing nanostructures, showing high absorption and low reflective coefficients, induce resonant absorption effects enhancing the electric acceleration field. The maximum kinetic energy measured for proton ions was above 5.0 MeV and the ion distributions can be fitted with Coulomb-Boltzmann shifted functions.

Characterization of thin films for TNSA laser irradiation

Thin films of hydrogenated materials have been prepared, at Messina University, to be irradiated by high intensity lasers in TNSA conditions in order to accelerate high energetic protons with high yield and directivity. Film composition was based on polymers, metals, multilayers and nanostructures embedded in polymers. The preparation methods were different and based on different deposition techniques. High vacuum condition, nanostructures, carbon nanotubes, metal oxides and hydrates, were employed. Targets were prepared as a sheath with thicknesses ranging between 0.1 and 100 μm and surfaces of the order of some cm2. Targets were characterized in terms of thickness, roughness, surface morphology, colours and absorption coefficient in the wavelength range 250 nm-1300 nm. Peculiar attention is given to samples with high absorption coefficient in order to improve the energy transfer from the coherent light to the generated plasma.

ELIMED: a new hadron therapy concept based on laser driven ion beams

Laser accelerated proton beams have been proposed to be used in different research fields. A great interest has risen for the potential replacement of conventional accelerating machines with laser-based accelerators, and in particular for the development of new concepts of more compact and cheaper hadrontherapy centers. In this context the ELIMED (ELI MEDical applications) research project has been launched by INFN-LNS and ASCR-FZU researchers within the pan-European ELI-Beamlines facility framework. The ELIMED project aims to demonstrate the potential clinical applicability of optically accelerated proton beams and to realize a laser-accelerated ion transport beamline for multi-disciplinary user applications. In this framework the eye melanoma, as for instance the uveal melanoma normally treated with 62 MeV proton beams produced by standard accelerators, will be considered as a model system to demonstrate the potential clinical use of laser-driven protons in hadrontherapy, especially because of the limited constraints in terms of proton energy and irradiation geometry for this particular tumour treatment. Several challenges, starting from laser-target interaction and beam transport development up to dosimetry and radiobiology, need to be overcome in order to reach the ELIMED final goals. A crucial role will be played by the final design and realization of a transport beamline capable to provide ion beams with proper characteristics in terms of energy spectrum and angular distribution which will allow performing dosimetric tests and biological cell irradiation. A first prototype of the transport beamline has been already designed and other transport elements are under construction in order to perform a first experimental test with the TARANIS laser system by the end of 2013. A wide international collaboration among specialists of different disciplines like Physics, Biology, Chemistry, Medicine and medical doctors coming from Europe, Japan, and the US is growing up around the ELIMED project with the aim to work on the conceptual design, technical and experimental realization of this core beamline of the ELI Beamlines facility.

Thomson parabola spectrometry of laser generated plasma at PALS laboratory

Laser generated Plasma has been obtained at PALS laboratory in Prague irradiating thin films by Target Normal Sheath Acceleration (TNSA) regime. The irradiated targets were polymers and metals with embedded nanostructures and different thicknesses. In the present work, plasma has been characterized by using Thomson Parabola Spectrometer placed in forward direction. The regime of laser intensity was of the order of 1016W/cm2 at 1.3 μm wavelength. Simulations performed by TOSCA code have been employed to compare theoretical prevision with experimental data. This approach permitted the recognition of parabolas and the evaluations of ion charge, energy and mass-to-charge ratio. Results revealed that the maximum ion acceleration is obtained n metallic foils for optimal thickness of the order of 10 μm and for target containing nanostructures responsible for the increase of the plasma electron density and resonant absorption effect, as will be presented and discussed.

A New Thomson Spectrometer for high energy laser-driven beams diagnostic

Thomson Spectrometers (TPs) are widely used for beam diagnostic as they provide simultaneous information on charge over mass ratio, energy and momentum of detected ions. A new TP design has been realized at INFN-LNS within the LILIA (Laser Induced Light Ion Acceleration) and ELIMED (MEDical application at ELI-Beamlines) projects. This paper reports on the construction details of the TP and on its experimental tests performed at PALS laboratory in Prague, with the ASTERIX IV laser system. Reported data are obtained with polyethylene and polyvinyl alcohol solid targets, they have been compared with data obtained from other detectors. Consistency among results confirms the correct functioning of the new TP. The main features, characterizing the design, are a wide acceptance of the deflection sector and a tunability of the, partially overlapping, magnetic and electric fields that allow to resolve ions with energy up to about 40 MeV for protons.

ELIMED: MEDICAL APPLICATION AT ELI-BEAMLINES. STATUS OF THE COLLABORATION AND FIRST RESULTS

ELI-Beamlines is one of the four pillars of the ELI (Extreme Light Infrastructure) pan-European project. It will be an ultrahigh-intensity, high repetition-rate, femtosecond laser facility whose main goal is to generate and apply high-brightness X-ray sources and accelerated charged particles. In particular, medical applications are treated by the ELIMED task force, which has been launched by collaboration between ELI and INFN researchers. ELIMED aims to demonstrate the clinical applicability of laser accelerated ions. In this article, the state of the ELIMED project and the first scientific results are reported. The design and realisation of a preliminary beam handling system and of an advanced spectrometer for diagnostics of high energy (multi-MeV) laser-accelerated ion beams will also be briefly presented.

Thomson Parabola Spectrometer for Energetic Ions Emitted from Sub-ns Laser Generated Plasmas

Laser-generated plasmas were obtained in high vacuum by irradiating micrometric thin films (Au, Au/Mylar, Mylar) with the Asterix laser at the PALS Research Infrastructure in Prague. Irradiations at the fundamental wavelength, 300 ps pulse duration, at intensities up to about 1016W/cm2, enabled ions to be accelerated in forward direction with kinetic energies of the order of 2 MeV/charge state. Protons above 2 MeV were obtained in the direction orthogonal to the target surface in selffocusing conditions. Gold ions up to about 120 MeV and 60+ charge state were detected. Ion collectors and semiconductor SiC detectors were employed in time-of-flight arrangement in order to measure the ion velocities as a function of the angle around the normal direction to the target surface. A Thomson parabola spectrometer (TPS) with a multi-channel-plate detector was used to separate the different ion contributions to the charge emission in single laser shots, and to get information on the ion charge states, energy and proton acceleration. TPS experimental spectra were compared with accurate TOSCA simulations of TPS parabolas.

TNSA and ponderomotive plasma production in enriched carbon polyethylene foils

Proton and carbon ion acceleration in a target-normal-sheath-acceleration regime produced by a laser intensity of 1016 W/cm2 was investigated using thin polyethylene foils. Measurements performed at the PALS facility in Prague demonstrate forward ion acceleration above 1 MeV per charge state. The ion acceleration is higher in thinner polymeric foils. In order to increase the emission yield of the proton and carbon ions, the target thickness should be enhanced, but this choice reduces drastically the ion acceleration. The use of highly absorbing stuff, such as carbon nanotubes embedded inside a polymer, enhances the ion acceleration but results in a broad ion energy distribution and a low amount of the highly accelerated ion species.