Laser-driven ion fast ignition (IFI) of fusion targets requires ultra-intense ion beams with parameters whose approximate values are estimated to be as follows (e. g. ): the mean ion energy ~10 – 50 MeV/nucleon, the beam intensity ~10^20
W/cm2, the beam fluence ~1 GJ/cm2, the ion pulse duration ~1 - 10 ps, and a total beam energy of ~10 – 20 kJ. To achieve these parameters, an effective ion acceleration scheme and a 100 kJ class picosecond laser driver is necessary. In this contribution, detailed properties of carbon ion beams driven by a 100-kJ, 1-ps laser is numerically investigated, and the possibility of attaining the ion beam parameters required for IFI through the use of an ultraviolet (0.25 um) or infrared (1.05 um) laser beam is discussed. The numerical simulations were performed for realistic, relevant for IFI parameters of the laser pulse and the carbon target using multi-dimensional (2D3V) particle-in-cell PICDOM code, which includes, in particular, the dynamic ionisation of the target and radiation losses due to synchrotron radiation. It was found that for relatively thin targets (LT < 10 um) and a laser beam diameter dL < 20 um, both the radiation pressure acceleration (RPA) mechanism and the sheath acceleration (SA) mechanism significantly affects the ion beam characteristics, and that the ion beam parameters such as the beam intensity, density and fluence are rather far from what is required, independent of the laser wavelength. In the case of thicker targets (LT ~20 – 40 um), the RPA in the hole-boring regime is a dominant mechanism of ion acceleration, and for dL ~10 um and a small distance from the target (x < LT) the ion beam parameters are close to or higher than what is required, both for the UV and IR laser beam. However, the angular divergence of the ion beam driven by the IR laser is smaller than that for the UV laser and, as a result, a decrease in the ion beam intensity and fluence with an increase in the distance from the target is slower for the IR laser-driven ion beam, which is essential for the application of the beam to the ignition of a real fusion target. Factors limiting the possibility of achieving ion beam parameters suitable for IFI will be discussed, along with possible ways to improve the ion beam parameters to better fit them to IFI requirements.
 J.C. Fernandez, B.J. Albright, F.N. Beg, M.E. Foord, B.M. Hegelich, J.J. Honrubia, M. Roth, R.B. Stephens, and L. Yin, Nucl. Fusion 54, 054006 (2014).
|Working group||Laser-driven ion acceleration|