Acceleration of carbon ion beams by an ultraviolet laser under conditions relevant for ion fast ignition of inertial fusion

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 similar to 10-30 mu m). 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 mu m to 30 mu m, 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 mu m) reach maximum values at L-T similar to 5-10 mu m. For the optimal value of L-T and a small distance x from the target (x similar to 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.