Studies on targets for inertial fusion ignition demonstration at the HiPER facility

Recently, a European collaboration has proposed the High Power Laser Energy Research (HiPER) facility, with the primary goal of demonstrating laser driven inertial fusion fast ignition. HiPER is expected to provide 250 kJ in multiple, 3omega (wavelength lambda = 0.35 mum), nanosecond beams for compression and 70 kJ in 10-20 ps, 2omega beams for ignition. The baseline approach is fast ignition by laser-accelerated fast electrons; cones are considered as a means to maximize ignition laser-fuel coupling. Earlier studies led to the identification of an all-DT shell, with a total mass of about 0.6 mg as a reference target concept. The HiPER main pulse can compress the fuel to a peak density above 500 g cm-3 and an areal density rhoR of about 1.5 g cm-2. Ignition of the compressed fuel requires that relativistic electrons deposit about 20 kJ in a volume of radius of about 15 mum and a depth of less than 1.2 g cm-2. The ignited target releases about 13 MJ. In this paper, additional analyses of this target are reported. An optimal irradiation pattern has been identified. The effects on fuel compression of the low-mode irradiation non-uniformities have been studied by 2D simulations and an analytical model. The scaling of the electron beam energy required for ignition (versus electron kinetic energy) has been determined by 2D fluid simulations including a 3D Monte Carlo treatment of relativistic electrons, and agrees with a simple model. Integrated simulations show that beam-induced magnetic fields can reduce beam divergence. As an alternative scheme, shock ignition is studied. 2D simulations have addressed optimization of shock timing and absorbed power, means to increase laser absorption efficiency and the interaction of the igniting shocks with a deformed fuel shell.