Inertial confinement fusion (ICF) is currently one of the two main paths towards an energy source based on thermonuclear fusion. A promising ICF option is ion fast ignition (IFI), in which the ignition of nuclear fuel is initiated by an intense laser-driven ion beam. This paper presents the results of systematic numerical (particle-in-cell) studies of the properties of laser-driven carbon ion beams produced under conditions relevant for IFI, and the feasibility of achieving beam parameters required for fuel ignition is discussed. It was found that a 1 ps 200 kJ infrared laser driver is capable of producing ion beams with parameters required for IFI, even with a simple non-optimised target, but only at small distances (⩽0.1 mm) from the target. At such distances, the beam intensity and fluence exceeds 5 × 1021 W cm−2 and 2 GJ cm−2, respectively, while the beam energy approaches 30 kJ. The ion beam parameters can be significantly improved by carefully selecting the target thickness and shape. However, even with an optimised target, achieving the beam parameters required for IFI is possible only at distances from the target below 0.5 mm. The ion acceleration is accompanied by the emission of powerful (⩾50 PW) pulses of short-wavelength synchrotron radiation which are the source of significant ion energy losses and may pose a threat to the fusion infrastructure. In addition to ICF, the extremely intense ion beams demonstrated in the paper can be a unique research tool for research in nuclear physics, high energy-density physics or materials science.

The multi-petawatt (PW) lasers currently being built in Europe as part of the Extreme Light Infrastructure (ELI) project will be capable of generating femtosecond light pulses of ultra-relativistic intensities (~1023–1024 W/cm2) that have been unattainable so far. Such laser pulses can be used for the production of high-energy ion beams with unique features that could be applied in various fields of scientific and technological research. In this paper, the prospect of producing ultra-intense (intensity ≥1020 W/cm2) ultra-short (pico- or femtosecond) high-energy ion beams using multi-PW lasers is outlined. The results of numerical studies on the acceleration of light (carbon) ions, medium-heavy (copper) ions and super-heavy (lead) ions driven by a femtosecond laser pulse of ultra-relativistic intensity, performed with the use of a multi-dimensional (2D3 V) particle-in-cell code, are presented, and the ion acceleration mechanisms and properties of the generated ion beams are discussed. It is shown that both in the case of light ions and in the case of medium-heavy and super-heavy ions, ultra-intense femtosecond multi-GeV ion beams with a beam intensity much higher (by a factor ~102) and ion pulse durations much shorter (by a factor ~104–105) than achievable presently in conventional radio frequency-driven accelerators can be produced at laser intensities of 1023 W/cm2 predicted for the ELI lasers. Such ion beams can open the door to new areas of research in high-energy density physics, nuclear physics and inertial confinement fusion.

The paper reports the results of numerical studies on the generation of heavy ions from a sub-micrometre gold target irradiated by a high-energy (60 J) high-intensity (~ 2 x 10 20 W/cm 2 ) sub-ps laser pulse. The properties of the heavy ion beam produced from a 0.5-um gold target with and without hydrogen contaminants are investigated using a multi-dimensional (2D3V) particle-in-cell code. It was found that in the case of the pure (without the contaminants) target, the ion beam contains over 20 ion species with a charge state > 30 and a total number of high-energy (> 20 MeV) ions reaching values well above 10 12 . The ion energy spectrum is broad, with maximum energies > 1 GeV and mean energies > 100 MeV. At a distance ~ 1 mm from the target, the intensity of the ion beam is ~ 10 15 W/cm 2 , the ion fluence reaches ~ 10 16 ions/cm 2 , and the ion pulse duration is ~ 100 ps. The contaminants significantly reduce the ion beam parameters and both the mean ion energy and the intensity and fluence of the ion beam generated from the contaminated gold target are almost an order of magnitude lower than those produced from the pure target. Heavy ion beams with the parameters obtained in the case of the pure gold target are barely achievable in conventional RF-driven accelerators, so they can open the door to new areas of research, in particular in high energy-density physics.

The properties of carbon ion beams produced by a 100-kJ, 1-ps, KrF ultraviolet laser under conditions relevant for ion fast ignition (IFI) of DT fusion are numerically investigated using the 2D3V particle-in-cell code, and the possibility of achieving the ion beam parameters required for IFI is tested. The numerical simulations of carbon ion acceleration were carried out for flat carbon targets of various thicknesses (L T ) and for various laser beam apertures (d L ) on the target, while the laser pulse duration and energy were fixed. It was found that both the radiation pressure acceleration (RPA) mechanism and the sheath acceleration mechanism significantly affects the characteristics of the ion beam, with the RPA dominating in the case of thicker targets (L T ∼ 10-30 µm). The ion beam parameters depend to a significant extent on the target thickness and the distance from the target. The mean and maximum ion energy decrease with the increase of L T from 3 µm to 30 µm, while the ion beam intensity, the beam energy fluence and the total energy of the "useful part" of the ion beam (with an aperture ≤ 50 µm) reach maximum values at L T ∼ 5-10 µm. For the optimal value of L T and a small distance x from the target (x ∼ L T ), the ion beam parameters are close to or higher than what is required for IFI. However, due to the angular divergence of the ion beam, the beam intensity and fluence decrease with an increase in the distance from the target, and at x ≥ 0.5 mm the beam parameters are below the values required for fusion ignition. To reach these values, higher laser energies and/or more sophisticated schemes of ion acceleration are required. K: Accelerator modelling and simulations (multi-particle dynamics; single-particle dynamics); Ion sources (positive ions, negative ions, electron cyclotron resonance (ECR), electron beam (EBIS)

No abstract