Maximum Ion Acceleration Research Articles

Ion acceleration from aluminised mylar film irradiated by visible ns-pulsed laser

A ns-pulsed laser operating at 532 nm wavelength has been employed to irradiate micrometric mylar films (1–100 μm) with an attached 0.1 μm Al film on its back face. Protons and light ions have been accelerated by the electric field developed in the non-equilibrium plasma generated by the laser pulse in a vacuum at an intensity of the order of 1010 W/cm2. The Time-of-flight (TOF) technique, using a Faraday cup (ion collector) coupled to a fast storage oscilloscope, has been employed to measure the ion velocity, energy and yield. The yield of plasma-emitted photons has been also evaluated. Two ion collectors have been used in opposite directions to measure the maximum ion acceleration by the TOF data acquired in backward and forward directions and the photon yield as a function of the target thickness. The evaluation of the ion energy distribution has been based on the Coulomb-Boltzmann-Shifted (CBS) distribution function.

Aluminum ion plasma monitored by SiC detectors from low to high laser intensity and from ns up to fs pulse duration

Thick and thin films of Al targets were irradiated in vacuum with different IR lasers at intensities between 1010 W/cm 2 and 1019 W/cm2, with pulse duration ranging between 3 ns and 45 fs. The laser-generated plasma was monitored in forward and backward directions, from thin and thick targets, by using SiC detectors, ion collectors, ion energy analyzer, optical spectrometer, Thomson parabola spectrometer and X-ray streak camera. Ion emission shows a maximum ion acceleration proportional to the laser intensity, which reaches about 1 MeV per charge state at 1016 W/cm2. Using fs laser, Al ion acceleration occurs at energies up to about 26 MeV and protons are accelerated at energies up to about 2.0 MeV.In the used experimental conditions, the maximum ion acceleration can be controlled by the laser parameters, irradiation conditions, and target geometry, such as the pulse energy, the focal position and the target thickness. Although different lasers and irradiation conditions were employed, the produced ion charges per solid angle of detection remain comparable, as it will be discussed.

Achievement of Laser Fusion with High Energy Efficiency Using a Mixture of D and T Ions

A mixture of deuterium (D) and tritium (T) is the most likely fuel for laser-driven inertial confinement fusion (ICF) reactors and hence DD and DT are the fusion reactions that will fire these reactors in the future. Neutrons produced from the two reactions will escape from the burning plasma, in the reactor core, and they are the only products possible to be measured directly. DT/DD neutron ratio is crucial for evaluation of T/D fuel ratio, burn control, tritium cycle and alpha particle self-heating power. To measure this ratio experimentally, the neutron spectra of DD and DT reactions have to be measured separately and simultaneously under high neutron counting with sufficient statistics (typically within 10% error) in a very short time and these issues are mutually contradicted. That is why it is not plausible to measure this high priority ratio for reactor performance accurately. Precise calculations of the DT/DD neutron ratio are needed. Here, we introduce such calculations using a three dimensional (3-D) Monte Carlo code at energies up to 40 MeV (the predicted maximum ion acceleration energy with the available laser systems). In addition, the fusion power ratio of DD and DT reactions is calculated for the same energy range. The study indicates that for a mixture of 50% deuterium and 50% triton, with taking into account the reactions D(d,n)3He and T(d,n)4He, the optimum energy value for achieving the most efficient laser-driven ICF is 0.08 MeV.

Ion acceleration from intense laser-generated plasma: methods, diagnostics and possible applications

Abstract Many parameters of non-equilibrium plasma generated by high intensity and fast lasers depend on the pulse intensity and the laser wavelength. In conditions favourable for the target normal sheath acceleration (TNSA) regime the ion acceleration from the rear side of the target can be enhanced by increasing the thin foil absorbance through the use of nanoparticles and nanostructures promoting the surface plasmon resonance effect. In conditions favourable for the backward plasma acceleration (BPA) regime, when thick targets are used, a special role is played by the laser focal position with respect to the target surface, a proper choice of which may result in induced self-focusing effects and non-linear acceleration enhancement. SiC detectors employed in the time-of-flight (TOF) configuration and a Thomson parabola spectrometer permit on-line diagnostics of the ion streams emitted at high kinetic energies. The target composition and geometry, apart from the laser parameters and to the irradiation conditions, allow further control of the plasma characteristics and can be varied by using advanced targets to reach the maximum ion acceleration. Measurements using advanced targets with enhanced the laser absorption effect in thin films are presented. Applications of accelerated ions in the field of ion source, hadrontherapy and nuclear physics are discussed.

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.

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.

Neutron yields of nuclear reactions induced by ion acceleration in carbon-deuterated plasma produced by ultra-intense lasers

Neutron yields of the nuclear reactions induced by accelerated deuterium or carbon ions when solid deuterated targets (CD or CD2) are irradiated by ultra-intense lasers have been investigated. The energies of the accelerated ions have been calculated at different laser intensities. Nuclear reactions that have threshold energies less than the maximum ion acceleration, in each case, have been studied in detail. The mechanisms of these reactions, at different ion energies, have been discussed and the relevant cross sections have been calculated to compare the neutron yield of each reaction with that of the fusion reaction D(d,n)3He. The study indicates that at a certain value of laser intensity, when the accelerated ion energy is sufficient, the energy spectrum of the neutron yields of the reactions D(d,np)D, 12C(d,n)13N, 12C(d,np)12C and D(12c,n)13N will overlap with the spectrum of the neutron yield of the D(d,n)3He reaction. Then, it is impossible to distinguish the different neutron yields experimentally despite the fact that the total neutron yield can be measured. However, by calculating the relative importance of the neutron yield of each reaction, the contribution of the fusion reaction to the total neutron yield can be estimated. Our calculations point out that the total neutron yield of the reactions 12C(d,n)13N and D(12c,n)13N can exceed the neutron yield of the D(d,n)3He reaction. Also, the total neutron yield of the breakup reactions D(d,np)D and 12C(d,np)12C is comparable with the neutron yield of the D(d,n)3He reaction and the produced neutrons will overlap the 2.45 MeV neutrons.

Effect of initial plasma density on laser induced ion acceleration

The effect of initial plasma density on the energetics of the laser accelerated ions is studied using one dimensional particle in cell simulations. It is observed that the initial plasma density plays an important role in the generation of high energy particles. In the case of a spatially constant initial density, there exists an optimum value for the maximum ion acceleration. Similarly for the case of a density ramp, an optimum value of ramp length exists for the maximum ion acceleration. At a laser intensity of 5×1020 W/cm2, a maximum energy of about 1 GeV is seen with an optimum initial density ramp.

Fast Ion Bunch Generation by Ultraintense Laser Pulse on Plasma Foil Target

Particle-in-cell (PIC) simulations of fast particles produced by a short laser pulse with a duration of 40 fs and an intensity of 1020 W/cm2 interacting with a foil target are performed. The dependence of the energy of the generated fast ions on the target geometry is examined. The absorbed laser energy is transferred to fast electrons, which interact with the foil and are partially ejected from the foil surfaces. These electrons produce an electric field that causes an ion beam to be emitted from the rear surface of the foil. Three different kinds of target are considered. The optimum target plasma conditions for the maximum ion acceleration are determined.