L. Giuffrida

Full characterization of laser-accelerated ion beams using Faraday cup, silicon carbide, and single-crystal diamond detectors

Multi-MeV beams of light ions have been produced using the 300 picosecond, kJ-class iodine laser, operating at the Prague Asterix Laser System facility in Prague. Real-time ion diagnostics have been performed by the use of various time-of-flight (TOF) detectors: ion collectors (ICs) with and without absorber thin films, new prototypes of single-crystal diamond and silicon carbide detectors, and an electrostatic ion mass spectrometer (IEA). In order to suppress the long photopeak induced by soft X-rays and to avoid the overlap with the signal from ultrafast particles, the ICs have been shielded with Al foil filters. The application of large-bandgap semiconductor detectors (>3 eV) ensured cutting of the plasma-emitted visible and soft-UV radiation and enhancing the sensitivity to the very fast proton/ion beams. Employing the IEA spectrometer, various ion species and charge states in the expanding laser-plasma have been determined. Processing of the experimental data based on the TOF technique, including est...

Fusion energy using avalanche increased boron reactions for block-ignition by ultrahigh power picosecond laser pulses—ERRATUM

Exceptionally high reaction gains of hydrogen protons measured with the boron isotope 11 are compared with other fusion reactions. This is leading to the conclusion that secondary avalanche reactions are happening and confirming the results of high-gain, neutron-free, clean, safe, low-cost, and long-term available energy. The essential basis is the unusual non-thermal block-ignition scheme with picosecond laser pulses of extremely high powers above the petawatt range.

Single crystal silicon carbide detector of emitted ions and soft x rays from power laser-generated plasmas

A single-crystal silicon carbide (SiC) detector was used for measurements of soft x rays, electrons, and ion emission from laser-generated plasma obtained with the use of the Prague Asterix Laser System (PALS) at intensities of the order of 1016 W/cm2 and pulse duration of 300 ps. Measurements were performed by varying the laser intensity and the nature of the irradiated target. The spectra obtained by using the SiC detector show not only the photopeak due to UV and soft x-ray detection, but also various peaks due to the detection of energetic charged particles. Time-of-flight technique was employed to determine the ion kinetic energy of particles emitted from the plasma and to perform a comparison between SiC and traditional ion collectors. The detector was also employed by inserting absorber films of different thickness in front of the SiC surface in order to determine, as a first approximation, the mean energy of the soft x-ray emission from the plasma.

Measurements of electron energy distribution in tantalum laser-generated plasma

The time and space resolved characterization of laser-generated pulsed plasmas is useful not only for the comprehension of basic phenomena involved in the plasma generation and following supersonic expansion, but it also permits to control the nonequilibrium process that is useful for many applications (e.g., ion implantation). The “on-line” characterization can be performed by means of Langmuir probes, ion collectors, and ion energy analyzers, in order to measure the plasma temperatures and densities of atoms, ions, and electrons. The investigated plasmas were generated by means of laser pulses with intensity of the order of 109 W/cm2. The contemporary characterization of the electron (through the Langmuir probe) and ion energy distribution functions, EEDF and IEDF, respectively, permits to correlate the ion properties, like charge states and temperatures, with the electron properties, like the shape of the EEDF at different times and distances from the ablated target surface.

Protons and ion acceleration from thick targets at 1010 W/cm2 laser pulse intensity

Proton ion acceleration via laser-generated plasma is investigated at relatively low laser pulse intensity, on the order of 10 10 W/cm 2 . Time-of-flight technique is employed to measure the ion energy and the relative yield. An ion collector and an ion energy analyzer are used with this aim and to distinguish the number of charge states of the produced ions. The kinetic energy and the emission yield are measured through a consolidated theory, which assumes that the ion emission follows the Coulomb-Boltzmann-Shifted function. The proton stream is generated by thin and thick hydrogenated targets and it is dependent on the free electron states, which increase the laser absorption coefficient and the ion acceleration. The maximum proton energy, of about 200 eV, and the maximum proton amount can be obtained with thick metallic hydrogenated materials, such as the titanium hydrate TiH 2 .

Petawatt laser pulses for proton-boron high gain fusion with avalanche reactions excluding problems of nuclear radiation

An alternative way may be possible for igniting solid density hydrogen-11B (HB11) fuel. The use of >petawatt-ps laser pulses from the non-thermal ignition based on ultrahigh acceleration of plasma blocks by the nonlinear (ponderomotive) force, has to be combined with the measured ultrahigh magnetic fields in the 10 kilotesla range for cylindrical trapping. The evaluation of measured alpha particles from HB11 reactions arrives at the conclusion that apart from the usual binary nuclear reactions, secondary reactions by an avalanche multiplication may cause the high gains, even much higher than from deuterium tritium fusion. This may be leading to a concept of clean economic power generation.

Surface ion implantation induced by laser-generated plasmas

Surface ion implantation induced by laser-generated plasmas was investigated using the PALS Prague laser facilities. Cu, Ge, Ag and Ta ions were obtained through the ablation of solid targets in vacuum by means of 1015 W/cm2 laser pulses. Energetic ions (∼ 0.1–1 MeV) were implanted on different substrate surfaces (Si, C, Al, Ti and polyethylene) placed at different distances from the target and angles from the normal to the target surface. In order to increase the ion dose, implantation was performed by using more laser shots in the same experimental conditions. An ion energy analyzer was employed for online measurements of the ion energies and charge states produced by the laser plasma. Off-line Rutherford backscattering spectroscopy (RBS) of alpha particles allowed us to determine the ion depth profiles, the ion energies and the ion amount implanted on the substrate surfaces. RBS spectra have shown typical implanted deep profiles only for substrates placed along the normal to the target surface at which the ion energy is maximum. At large angles, no implantation occurs and ions are only deposited. At a high dose, the multi-energetic ion implantation can be used to modify the physical and chemical properties of the implanted layer surfaces.

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.

Data elaboration of proton beams produced by high-energy laser-generated plasmas

The proton beam production from high-energy laser-generated plasma is increasingly becoming of special interest for investigations in the field of new techniques of ion acceleration, nuclear physics, astrophysics and radiotherapy. The evolution of short-pulsed lasers, from the nanosecond to the femtosecond pulse scale, has allowed for an increase in intensity from about 1010 W/cm2 to about 1020 W/cm2 with a consequent increase of the kinetic energy of the plasma-generated ions. Thus proton energy has increased from about 100 eV at low intensity to about 100 MeV at the actual femtosecond-terawatt lasers. Although the emitted ions are multi-energetic, the use of thin hydrogenated targets and a high repetition rate can be employed to obtain high proton energy, narrow energy spread, high ion directivity and high current. Literature data indicate that the proton energy, the equivalent plasma temperature and the Coulomb acceleration increase with the pulse intensity. The use of femtosecond-terawatt lasers may produce very intense electric fields in the non-equilibrium plasma, which accelerate ions up to tens of MeV/amu. Ponderomotive forces, supersonic plasma expansion in vacuum, self-focusing effects and the high plasma temperature influence the ion plasma acceleration. Literature data can be fitted by Coulomb–Boltzmann-shifted functions which permit a separation of the thermal contribution from the Coulomb one. The latter increases at very high laser intensities to a greater extent than its thermal counterpart.

LAMQS and XRF analyses of ancient Egyptian bronze coins

A set of Egyptian bronze coins, dating back to the sixth or seventh century AD, has been studied by different experimental techniques in order to compare their composition and surface morphology, the process of coinage and, possibly, to also identify the place of production. The measurements have been performed by laser ablation with mass quadrupole spectrometry and energy dispersed X-ray fluorescence. Both analyses are non-invasive and can be safely used according to the integrity requirements of the analyzed pieces. Owing to the poor number of available samples, this work, more than to solve a numismatic question, has been carried out in order to test the validity of the above experimental techniques in view of further analyses on the same coins, based on better quality statistics. The preliminary results, presented in this paper, indicate significant differences in the chemistry of the coins’ patina, i.e. composition and isotopic species content. This seems to support, in agreement with the archaeological expectations, the hypothesis of the existence of a local mint in Antinoopolis, never before considered in Egyptian numismatics.