[en] Implosions of a target pellet exposed to an intense laser light are investigated numerically by using the spherically symmetric hydrodynamic equations. In order to obtain the maximum out put of the fusion energy from the pellet, the following facts are pointed out: (1) There is the optimum value of the laser intensity: (2) It is effective to replace the outside part of the critical density of the target plasma by a substance with a heavier particle mass: (3) For large pellets, a larger laser power is efficient: (4) There is the optimum shape of the laser pulse: (5) More out put energy is yielded from a pellet with a larger radius when the power and the pulse shape of the laser light are optimum. (auth.)

[en] A new model of implosion is proposed and the possibility of stable implosion is discussed on the basis of this model. The model indicates a relaxation of the restrictions on the peak power and the culmination time of laser light required for pellet implosion. (author)

[en] The particle-in-cell (PIC) method, which is known as mixed Eulerian-Lagrangian scheme, has been applied successfully to solve a wide variety of problems in which the fluid distortion is large. In this paper, a new type of the PIC method is presented. Area-weighting technique and a nonuniform-spacing, moving grid were employed for the suppression of nonphysical fluctuation and for the description of large density variation with few particles, respectively. The reduction of numerical viscosity is discussed. In a basic scheme, the equations for one compressible fluid were used. In the present approach to the PIC method, a particle has the memories for its own mass, position and internal energy, but momentum is attached to the particle only when it moves, in order to evade the multistreaming problem. An essential point is that a particle preserves the memory of the cell boundary lines when it moves. As the examples, one-dimensional adiabatic expansion process and the Rayleigh-Taylor instability were analyzed. The results showed that the new PIC method is useful for the description of large density variation with few particles as well as for the cases known to be powerful in Harlow's PIC method. Nonphysical noise, numerical thermal diffusion and viscosity were successfully reduced. A nonuniformly-spacing, moving grid system can be used for the local fine resolution of processes. (Kato, T.)

[en] The scheme for stable implosion is proposed and discussed. The asymptotic theory which is one branch of homogeneous isentropic compression scheme is derived and ascertained by numerical simulations. (auth.)

[en] The new flux-limited theory including the ion-wave effects is presented. Preliminary results of the two-dimensional particle simulations support this theory. (auth.)

[en] We present a one-dimensional analytical model which can be applied to the super-compression of the multistructured pellet. The main result shows that the time dependence of the input power E for the optimal compression is given by E proportional to (1 - t/tsub(s))sup(-3(G+1)/2G) where G=(rho₁/rho₂)sup(1/4), rho₁ and rho₂ are the densities of the D-T fuel and the high Z material respectively, and tsub(s) if the characteristic time interval. (auth.)

[en] An analytical model is presented which is applicable to the super-compression of the multi-structured slab. The main purpose of this paper is to clarify: (1) the effects of structured target; (2) the relation between the absorbed laser energy and the mechanical power supply at the critical surface; (3) the validity for neglecting the thermal conduction in the target. The condition is derived that shock waves launched from the ablation surface reach simultaneously the center of the multi-structured slab. The deflagration condition at the abalation surface is then discussed. The time dependence of the input power of the laser light to obtain an optimal compression of the target is also given. The relation between the absorbed laser energy in the slab and the mechanical power supply for compression is described along with the effects of thermal conduction

[en] A one-dimensional analytical model is applied to super-compression of a structured slab. The time dependence of the laser light input power is derived to obtain optimum compression of structured slabs. The effect of thermal conduction on the compression is also considered. (author)

[en] A strong dependence of implosion symmetry on laser focusing conditions and a growth of a whisker-like irregularity on ablation surface were observed in ablatively compressed laser fusion pellets by using time-resolved x-ray shadowgraphy. The time development of the implosion nonuniformity was traced by a 2-D fluid PIC code. The simulation result supports a hydrodynamic ''free-falling'' effect on the growing irregularity, which explains well the experimental results quantitatively within a factor of 2. (author)

[en] The dynamical stability of the implosion of a laser-driven pellet is investigated by using the linearized three-dimensional and nonlinear two-dimensional hydrodynamic equations. In these calculations, the following conclusions are obtained: 1) The growth rate of a perturbation is very sensitive to the way how the laser energy is supplied in time into the pellet. 2) The region where the perturbation has a positive growth rate varies with the wave length of the perturbation. 3) The growth of a perturbation is sensitive to the pellet structure. 4) Nonlinear mechanisms have a tendency to stabilize the perturbations. (auth.)