Ion source by laser-generated plasmas and relative diagnostics

The aim of my PhD was the study and characterization of plasmas produced by laser- matter interaction, the relative diagnostics, the mechanism of ion production and acceleration and some possible applications. The choice of this topic is to be sought at in the strong impact it has in modern research. The use of lasers as ion and electron accelerating systems and like x-ray source can certainly have a strong influence on the community, if laser-generated plasmas could be used as new types of ion accelerators, it would meet new scenarios for adronic therapy, with considerable savings in economic terms the current cost of accelerators. Moreover, such systems allow, potentially, to be able to obtain any type of nuclear reaction and consequently also nuclear fusion reactions. A controlled fusion reactor would be a solution to many social and environmental problems. In the last years, in fact, several laboratories and facilities have been built, not only to study the basic physics related to the formation and expansion of non-equilibrium plasmas generated by pulsed lasers, but also to realize possible applications. For example, at the National Ignition Facility of the Lawrence Livermore National Laboratory there is a high-power laser facility especially used to perform experiments on Inertial Confinement Fusion. At the LULI laser laboratory in France, that is one of the most powerful in the world (laser intensity up to 1020 W/cm2), studies regarding inertial confinement fusion, particle acceleration, shock waves, X-rays and γ − rays produced by laser ablation are carried out. Brookhaven National Laboratory in USA and the RIKEN laboratory in Japan are developing facilities in order to inject ions produced by laser-generated plasmas into classical particle accelerators for improving their energy and producing new nuclear reactions induced by heavy elements. An experiment that followed this idea was performed in 2002 at LNS-INFN laboratory of Catania, using an hybrid ion source (LIS-ECRIS). The new idea was to couple an equilibrium plasma, created by a classical ECR ion source, with a non-equilibrium plasma, created by pulsed laser ablation, in order to obtain high currents of highly charged ion beams to be injected inside the cyclotron. In this thesis work I deal with the diagnostics of ions produced in a non-equilibrium plasma generated by pulse laser ablation. Ion detection was mainly performed by using two types of electrostatic devices: ion collector (IC) and ion energy analyzer (IEA). Other kind of diagnostics are explained in this thesis in order to provide a complete panorama on the possible diagnostics that can be used in the study of plasma. The measures reported in this thesis were mainly conducted in three laboratories: Laser-Plasma laboratory of Department of Physics of Messina, CELIA Laboratory in Bordeaux and Brookhaven National Laboratory in New York State. In this thesis the first chapter is an introduction about the definition of plasma state, the characteristics of plasma that we are able to measured and the plasma production from laser-matter interaction. This interaction can be performed using several condition and the plasma properties depend strongly from these. We will see like the plasma production by laser ablation depends from laser wavelength and fluence and once the ablation threshold has passed the laser energy is assorbed by the plasma in order to accelerate the particles present in the plasma, like electron and ions. Speaking about the particles energy we will study the particle energy distributions, in the last years was developed by L.Torrisi (2016. REDS 171:1-2, 34-44) a model in wich the ion velocity depends on many factors of which the most important are the plasma temperature, the adiabatic gas expansion in vacuum and the Coulomb acceleration. The ion energy distributions of the emitted ions from the plasma can be well explained by the Coulomb–Boltzmann-Shifted function, with a cut-off limitation at high energy for a wide range of laser intensities. The at the end of the chapter will be show the regime for ion acceleration that depends from the laser intensity and target thickness. These regimes cover the laser intensity range from 10^9 − 10^22 W/cm^2 for relative ion energies from 100 eV/z up to 100 MeV/z. In the second chapter are presented several diagnostic techniques useful for the determination of ion energy, plasma temperature, neutral particles detection and optical measurement of plasma properties. The diagnostic techniques can be divided in on line and off line diagnostic, using time of flight techniques or other to understand quickly the plasma properties during the experiment, while the off-line diagnostics are studies performed after the experiment on the target or on the detector that need of some kind of treatment to see the result, examples are the study of surface profile obtained on the crater created on the target during the interaction and the track detector CR 39 that need of chemical etching in order to understand the energy of particles that interacted with the detector. Some diagnostics use the trajectory deflection that undergo the charged particles through electrical and / or magnetic fields, these techniques are described in third chapter where are described the Ion Energy Analyzer (IEA) that consist of in 90° electrostatic deflector developed for the construction of ion energy distribution per charge state of the ionic species present in the plasma. The limitation of this device consist of in the big number of laser shots needed for the analysis. For this reason many peaple are developed the use of Thomson Parabola Spectrometer (TPS) that use the deflection due to the presence of a Magnetic and an Electric fields. In a typical TPS, a pencil beam of ions, selected by the pinhole located at its entrance, travels through regions of parallel magnetic and electric fields applied transversely to the beam axis. The magnetic field de- termines the y-coordinate of the ions on the detector, depending on their energy, while the electric field deflects the ions along the x-axis according to their Z/A ratio. The last device described in the third chapter is a magnetic spectrometer developed inside our laboratory that consist of in a fixed magnetic field and in a multi faraday cup system for the analysis of angular distribution of plasma with and without magnetic field. This system allows to study many properties of plasma producing in several acceleration regime. The fourth chapter is very important because describe the experiment performed in Brookhaven National Laboratory and in Messina laboratory for the experimental studies of heavy ion beam generation from laser ablation plasma of gold coated aluminum target sample using IEA system at two different laser intensities. The experiments were performed with the main aim to study the produced plasma for Ion Source applications. Last chapter is a description of applications in Plasma Source for Ion Acceleration, are described devices like Radio Frequency Quadrupole (RFQ) and Superconducting Cyclotrone for the Ion Acceleration and the method that can be developed for the use of Laser Ion Source like main source of these systems. The post acceleration systems are important part of the discussion because in addition to the application in accelerator can be used for the Ion Implantation, a very important technique used in material studies. The last part of the chapter describe the results that can be obtained in ion acceleration using high intensity lasers and advanced targets. Finally, achievements and future prospects will be discussed in the conclusions.