Laser-driven acceleration of ion beams for ion fast ignition: the effect of the laser wavelength on the ion beam properties

The properties of a carbon ion beam accelerated by an infrared (1.05 mu m), visible (0.53 mu m) or ultraviolet (0.248 mu m) 1 ps 150 kJ laser under conditions relevant for ion fast ignition (IFI) are numerically investigated using a particle-in-cell 2D3V code, and the feasibility of achieving the ion beam parameters required for IFI is discussed. It was found that parameters of the ion beam determining the DT fuel ignition relatively weakly depend on the laser wavelength, and that each of the considered laser drivers enables the production of an ion beam with parameters required for IFI, but only at short distances from the irradiated carbon target, no longer than similar to 100 mu m. At such distances, a picosecond ion beam with 'useful' energy >10 kJ, peak fluence >1 GJ cm(-2), peak intensity >10(21) W cm(-2) and the mean ion energy similar to 500-600 MeV is produced regardless of the laser driver wavelength. The main factors limiting the possibility of achieving the required parameters of the ion beam at larger distances are the beam angular divergence and the ion velocity dispersion. The ion acceleration is accompanied by the emission of powerful (tens of PW, tens of kJ) picosecond pulses of short-wavelength synchrotron radiation whose power and energy increases as the laser wavelength decreases. The emission of this radiation is a source of ion energy losses and significantly reduces the values of energy, fluence and intensity of the ion beam. In addition, the emitted multi-PW radiation may pose a threat to the fusion infrastructure.