Recent results and future prospects of laser fusion research at ILE, Osaka

Reviewed are the present status of the fast ignition researches. Since 1997, the fast ignition experiment and theory researches have been extensively continued at the Institute of Laser Engineering of Osaka University. In particular, the cone-shell target experiments and simulation research have been progressing. In order to demonstrate heating of imploded high density plasma to the ignition temperature, in the April of 2003, the construction of heating laser of 10 kJ/10 ps/1.06 μm (Laser for Fusion Experiment; LFEX), for FIREX-I (Fast Ignition Realization Experiment) has started. The fabrication of DT foam cryogenic cone target is also under development as a collaboration program between Osaka University and NIFS (National Institute for Fusion Science). The LFEX will be completed in 2008. After the completion of LFEX, the foam cryogenic cone shell target experiment will start in 2008. As a new approach toward a compact ignition, an impact fusion has been proposed, where the ablative acceleration to the order of 10⁸ cm/s is the key issue. The ablation acceleration related to the impact fusion has been explored by experiments.     

Progress in direct-drive inertial confinement fusion research at the laboratory for laser energetics

Direct-drive inertial confinement fusion (ICF) is expected to demonstrate high gain on the National Ignition Facility (NIF) in the next decade and is a leading candidate for inertial fusion energy production. The demonstration of high areal densities in hydrodynamically scaled cryogenic DT or D₂ implosions with neutron yields that are a significant fraction of the “clean” 1-D predictions will validate the ignition-equivalent direct-drive target performance on the OMEGA laser at the Laboratory for Laser Energetics (LLE). This paper highlights the recent experimental and theoretical progress leading toward achieving this validation in the next few years. The NIF will initially be configured for X-ray drive and with no beams placed at the target equator to provide a symmetric irradiation of a direct-drive capsule. LLE is developing the “polar-direct-drive” (PDD) approach that repoints beams toward the target equator. Initial 2-D simulations have shown ignition. A unique “Saturn-like” plastic ring around the equator refracts the laser light incident near the equator toward the target, improving the drive uniformity. LLE is currently constructing the multibeam, 2.6-kJ/beam, petawatt laser system OMEGA EP. Integrated fast-ignition experiments, combining the OMEGA EP and OMEGA Laser Systems, will begin in FY08.     

Update on design simulations for NIF ignition targets, and the rollup of all specifications into an error budget

Targets intended to produce ignition on NIF are being simulated and the simulations are used to set specifications for target fabrication and other program elements. Recent design work has focused on designs that assume only 1.0 MJ of laser energy instead of the previous 1.6 MJ. To perform with less laser energy, the hohlraum has been redesigned to be more efficient than previously, and the capsules are slightly smaller. Three hohlraum designs are being examined: gas fill, SiO₂ foam fill, and SiO₂ lined. All have a cocktail wall, and shields mounted between the capsule and the laser entrance holes. Two capsule designs are being considered. One has a graded doped Be(Cu) ablator, and the other graded doped CH(Ge). Both can perform acceptably with recently demonstrated ice layer quality, and with recently demonstrated outer surface roughness. Complete tables of specifications are being prepared for both targets, to be completed this fiscal year. All the specifications are being rolled together into an error budget indicating adequate margin for ignition with the new designs. The dominant source of error is hohlraum asymmetry at intermediate modes 4–8, indicating the importance of experimental techniques to measure and control this asymmetry.     

The role of experimental science in ICF – examples from X-ray diagnostics and targets

The USA Inertial Confinement Fusion (ICF) Program evolved from the Nuclear Test Program which had restricted shot opportunities for experimentalists to develop sophisticated experimental techniques. In contrast the ICF program in the US was able to increase the shot availability on its large facilities, and develop sophisticated targets and diagnostics to measure and understand the properties of the high energy density plasmas (HEDP) formed. Illustrative aspects of this evolution at Lawrence Livermore National Laboratory (LLNL), with examples of the development of diagnostics and target fabrication are described.