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For the fast ignition of laser fusion, a reliable target design is required for an ignition scale target. This paper shows the first optimized target design for the implosion phase of fast ignition, which is scalable to larger targets. The requirements from the heating process are taken account. In conclusion, a target can be highly compressed using multi-step laser pulse irradiation to a solid spherical target with an inserted gold cone. In an 8 kJ scale implosion, the maximum areal density of deuterium–tritium fuel reaches 0.39 g cm−2 according to 2D simulation results, which is 62% of the case without the cone. Based on the similarity rule, we estimate that the requirement of the implosion laser energy for ignition scale targets (ρRmax  =1.0 g cm−2) is 135 kJ. [ABSTRACT FROM AUTHOR]

Laser lights with relativistic intensities and pulse lengths exceeding the picosecond (ps) have been recently made available. Laser–plasma interactions with such a parameter regime belong to the mesoscale between kinetic and fluid regimes, and thus theories developed for sub-ps laser–plasma interactions are not straightforwardly applicable to those for the multi-ps regime. We here study the generation of high-energy electrons in ps relativistic laser–foil interactions by using the particle-in-cell (PIC) simulation. We show that the dynamics of the laser hole boring, which stops during over-ps laser irradiation, is a key to generate the high energy electrons. An energy distribution with a high-energy tail cannot be fitted by a single Maxwellian function, and is likely to be a nonthermal distribution through a stochastic interaction via the recirculation of electrons in the expanding foil plasma. The present study of superthermal electron generation can be a basis for ps laser applications such as fast ignition-based laser fusion, laser ion acceleration, and short-pulse x-ray generation. [ABSTRACT FROM AUTHOR]

To enhance the core heating efficiency in fast ignition laser fusion, the concept of relativistic electron beam guiding by external magnetic fields was evaluated by integrated simulations for FIREX class targets. For the cone-attached shell target case, the core heating performance deteriorates by applying magnetic fields since the core is considerably deformed and most of the fast electrons are reflected due to the magnetic mirror formed through the implosion. On the other hand, in the case of a cone-attached solid ball target, the implosion is more stable under the kilo-tesla-class magnetic field. In addition, feasible magnetic field configuration is formed through the implosion. As a result, the core heating efficiency doubles by magnetic guiding. The dependence of core heating properties on the heating pulse shot timing was also investigated for the solid ball target. [ABSTRACT FROM AUTHOR]