Salvatore Cavallaro

Diamond detectors for characterization of laser-generated plasma

Diamond monocrystalline detectors were used to characterize radiation and particle emission from laser-generated plasma obtained at Laboratori Nazionali del Sud (LNS) and Plasma Asterix Laser Systems (PALS) laboratories by using a high power pulsed laser intensity of 1010 W/cm2 and 1016 W/cm2, respectively. Al, Ta, Au and CF2 plasmas were obtained in different irradiation conditions. Diamond detectors permitted to measure UV, X-rays, electrons and ions. Time-of-flight technique was employed to separate in time the different contributions. Results indicate that this detector has some advantages with respect to the others, such as the high energy gap, the high energy resolution, the low background current and the possibility to detect simultaneously photons, electrons and ions.

Ti post-ion acceleration from a laser ion source

Laser ion sources are employed with success to generate, in vacuum, any ion species with high current, ion energy, charge states and directivity. Nanosecond infrared laser pulses, with intensities of the order of 1010 W/cm2, induce ablation in metals. Ions are produced in vacuum with energy distribution following the Coulomb–Boltzmann-shifted distribution and are ejected mainly along the normal to the target surface. The free ion expansion process occurs in a constant potential chamber placed at high positive voltage variable between 0 and 30 kV, by means of nose along the normal to the target surface. The electric field reaches 5 kV/cm and is used to accelerate Ti ions emitted from the plasma at the INFN–LNS laser facility. The time-of-flight technique is employed to measure the mean ion energies of the post-accelerated particles. Ion charge states and energy distributions were measured through an ion energy spectrometer. Ion energies, charges per pulse, ion currents and beam directivity of Ti beams were measured, and the results were compared with those coming from simulation programs.

Proton emission from a laser ion source.

At intensities of the order of 10(10) W∕cm(2), ns pulsed lasers can be employed to ablate solid bulk targets in order to produce high emission of ions at different charge state and kinetic energy. A special interest is devoted to the production of protons with controllable energy and current from a roto-translating target irradiated in repetition rate at 1-10 Hz by a Nd:Yag pulsed laser beam. Different hydrogenated targets based on polymers and hydrates were irradiated in high vacuum. Special nanostrucutres can be embedded in the polymers in order to modify the laser absorption properties and the amount of protons to be accelerated in the plasma. For example, carbon nanotubes may increase the laser absorption and the hydrogen absorption to generate high proton yields from the plasma. Metallic nanostrucutres may increase the electron density of the plasma and the kinetic energy of the accelerated protons. Ion collectors, ion energy analyzer, and mass spectrometers, used in time-of-flight configuration, were employed to characterize the ion beam properties. A comparison with traditional proton ion source is presented and discussed.

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.

ELIMED a new concept of hadrontherapy with laser-driven beams

ELIMED (Medical Applications at Extreme Light Infrastructure) is a task-force originally born by an idea of ELI-Beams (Prague, CZ)and INFN-LNS (Italian Institute for Nuclear Physics of Catania, I) researchers. It now involves other groups interested in the possibility to design and develop a new generation of hadrontherapy facilities using laser-accelerated ion beams. ELIMED main goal is to perform proof-of-principle experiments aimed to demonstrate that laser-accelerated high-energy proton beams (up to 70 MeV in the first phase) can be potentially used for the specific case of ocular proton therapy. For this purpose new devices for beam handling and transport will be developed as well as new methods for radiobiology and dosimetry. The involvement of INFN-LNS group takes advantage of the well-established expertise in dosimetry measurements and Monte Carlo calculations for medical physics, which has been achieved in several years of eye tumor treatments in the CATANA proton therapy facility. Recently, in the framework of an INFN activity, they have also designed, fabricated, calibrated and experimentally tested at PALS laser laboratory (Cz) a Thomson Parabola ion spectrometer with a wide acceptance and able to characterize laser-driven proton beams up to 20 MeV.

Monoenergetic proton emission from nuclear reaction induced by high intensity laser-generated plasma.

A 10(16) W∕cm(2) Asterix laser pulse intensity, 1315 nm at the fundamental frequency, 300 ps pulse duration, was employed at PALS laboratory of Prague, to irradiate thick and thin primary CD(2) targets placed inside a high vacuum chamber. The laser irradiation produces non-equilibrium plasma with deutons and carbon ions emission with energy of up to about 4 MeV per charge state, as measured by time-of-flight (TOF) techniques by using ion collectors and silicon carbide detectors. Accelerated deutons may induce high D-D cross section for fusion processes generating 3 MeV protons and 2.5 MeV neutrons, as measured by TOF analyses. In order to increase the mono-energetic proton yield, secondary CD(2) targets can be employed to be irradiated by the plasma-accelerated deutons. Experiments demonstrated that high intensity laser pulses can be employed to promote nuclear reactions from which characteristic ion streams may be developed. Results open new scenario for applications of laser-generated plasma to the fields of ion sources and ion accelerators.

Detection of energetic ions emitted from laser-produced plasma by means of CR39 solid state nuclear track detectors

The iodine laser PALS, operated at the fundamental and third harmonic frequencies (wavelengths 1315 and 438 nm, respectively), was used to generate plasmas on various targets (Au,CF2, etc.). The investigation was performed at energies up to 400 and 250 J for 1ω and 3ω, respectively, in the 300 ps pulses. In these conditions several samples of solid state nuclear track detectors CR39 type, have been located at suitable geometrical positions to explore their capability to measure main parameters of ions emitted from the laser-produced plasmas. Track diameters and densities were observed on the uncovered detectors exposed to a lot of laser shots. Emitted ions in the energy range up to few tens of MeV, have been observed on the basis of ion collector TOF spectra. Track pattern results are shown and discussed in comparison with mentioned spectra and simulations.

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.