The direct drive laser is the key factor in hybrid drive inertial confinement fusion. Its drive asymmetry has a great influence on the ignition performance of nuclear fusion. Using the same laser power, the impacts of the direct drive laser focal spot size on the ignition performance of a hybrid drive model are studied. It is shown that the size of the laser focal spot is a key parameter to influence the ignition performance of the hybrid drive model. When the size of the laser focal spot is 1 500 μm, the neutron yield of the target is close to the one got by the one dimensional implosion. When the 1 400 μm laser focal spot is used, the neutron yield is 40% of the one got by the one dimensional implosion. However, it is failed to ignite for the 1 200 μm laser focal spot. The high drive asymmetry caused by the small laser focal spot can increase the adiabat in the fuel. The fuel compressibility will decrease when the adiabat is increased, which goes against creating the ignition condition. In this way, the ignition wave is weak. Meanwhile, the high drive asymmetry can lead a high perturbation of the fuel areal density. The perturbation growth of the fuel areal density can make the shell asymmetry grow greatly when the ignition wave is formed. Under the conditions of the weak ignition wave and the high fuel areal density perturbation, the fuel spike with a high density is hard to be ignited. Therefore, the positive feedback between the increase of hotspot temperature and the ignition is restrained. Meanwhile, the fuel spike can decrease the hotspot temperature. The fuel bubble can lead the hotspot expand rapidly. All these factors will make the ignition performance decrease when a small laser focal spot is used.

We report new progress in hybrid-drive (HD) ignition target design with a high-adiabat (>3.0) and high-velocity (>400 km·s^-1). First, two-shock indirect-drive (ID) radiation temperature with lower peak 200 eV ablates and pre-compresses the capsule. Later, direct-drive lasers of power 340 TW in flat-top pulse are absorbed near critical surface, combined with the radiation to drive the implosions. The "snowplow" effect in the HD heaps low ID corona density into a high HD plasma density at the radiation ablation front where maximal HD pressure reaches over 500 Mbar. Such high pressure further drives capsule imploding with peak velocity about 424.5 km·s^-1 and fuel aidabat about 3.4, and the high-velocity and high-adiabat lower the hotspot pressure required to ignition lower to about 200 Gbar at a low convergent ratio 23 to suppress hydrodynamic instabilities. 2D simulation also predicts the growth factor (GF) at hotspot is very small < 10, beneficial for a robust hotspot and further burn.

Test codes are programmed with C++ to study influence of pressure correction algorithms, including SIMPLE (Semi-Implicit Method for Pressure Linked Equations), SIMPLEC (SIMPLE Consistent), SIMPLER (SIMPLE Revised), SIMPLEX (SIMPLE Extrapolation) and PISO (Pressure-Implicit with Splitting of Operators), on numerical solution performance of Braginskii transport equation for scrape-off layer plasma. Plasma model equations of SOLPS (Scrape-Off Layer Plasma Simulation) are adopted in the test codes. Numerical calculations are carried out on a simplified slab model. It was found that all of the pressure correction algorithms make the program converge to correct results. The fastest convergence speed is achieved with PISO. There is no significant difference in the convergence speed of SIMPLE, SIMPLEC, SIMPLER and SIMPLEX algorithms.

Targeting at SN algorithm for the neutron transport equation in the two-dimensional spherical coordinate system, we propose a directed graph model based on a (cell, direction) two-tuple, and design a multi-level parallel SN algorithm with controllable granularity on the basis of the existing parallel pipeline algorithm based on directed graph. Among them, a combination of domain decomposition and parallel pipeline is used to mine parallelism in the space-angle direction, and an energy group pipeline parallel method is proposed. Furthermore, by setting appropriate pipeline granularity, the overhead of scheduling, communication and idle waiting are well balanced. Experimental results show that the algorithm can effectively solve the neutron transport equation in the two-dimensional spherical coordinate system. For a typical neutron transport problem with 960 000 grids, 60 directions, 24 energy groups, and billions of degrees of freedom, the parallel program achieved 71% parallel efficiency on 1920 cores of a domestic parallel machine.

We investigate collision characteristics of micro-sized particles (diameter less than 100 microns) via numerical simulations and experiments. Discrete element method (DEM) simulations, based on improved hard-sphere model, are performed to explore effect of initial velocity, surface energy, size, mass concentration, and wind speed on cohesive collisions and non-cohesive collisions between micro-sized particles. Aggregation and settlement process are considered as well. It is found that simulated cohesive collision rate agrees with experimental results of self-settlement of micro-sized particles.

Based on operator splitting technique, Euler equations is splitted into convection part and non-convection part. A predicted solution is obtained by solving the convection part with explicit GFM method. It is corrected by an implicit pressure correction algorithm derived from the non-convection part. A second order primitive explicit-implicit algorithm is built. It shows that CFL condition can be relaxed and efficiency is improved.

A Runge-Kutta discontinuous Galerkin(RKDG) method for conservation law with source term is shown.The method is implemented with Strang split or unsplit methods,and is applied to solve one-dimensional conservation law with source term as well as one and two-dimensional detonation wave problems.In order to compare with the fifth-order finite volume WENO method,a special reconstruction method is proposd to calculate integration of the source term with high-order spatial accuracy.Numerical tests in one dimension show that the RKDG method has smaller errors than WENO method for nonstiff problems and is more accurate in capturing position of discontinuity in stiff problems.Numerical simulations of detonation waves demonstrate that the RKDG method is more effcient in resolving detailed structure of detonation waves and location of detonation front.

In conventional ghost fluid method,Riemann problems are defined by taking direatly states at grid points as initial conditions.In this article,we improve this approach by taking states at interpolated points as initial conditions.States at interpolated points are obtained by area average of states at four surrounding grid points.Since initial conditions are smooth,our method gives results with less numerical oscillations.Numerical experiments illustrate that the method is effective.

Compressible two-fluid inviscid flow is computed by the Ghost Fluid method with Isobaric fix.The method can avoid numerical oscillation and smearing as is encountered with a shock-capturing scheme in computing fluid interface,and it is simpler to code than fronttracking techniques.The system of the Euler equations which describes the fluid flow and the level set equation which describes the interface motion is solved by high-resolution WENO finite difference scheme.Satisfatory results are obtained for several 1D and 2D compressible two-fluid flows subject to the stiffened equation of state.

The full approximation storage (FAS) multigrid algorithm is applied in conjunction with the artificial compressibility method to accelerate steady solutions of the 3D incompressible Navier Stokes equations. Neumann boundary conditions in terms of the solution correction are implemented on the coarse grid when solving the coarse grid equations. The basic scheme used is the diagonalized approximate factorization scheme, and the spatial difference for inviscid fluxes adopts both MUSCL scheme and symmetric TVD scheme respectively for comparing. The performance of the present method is studied for the entry flow through a 90° bent square duct and the flow past an inclined prolate spheroid with an axes ratio of 4:1. It is found that the proposed multigrid method can save the computing time by at least half, and that MUSCL scheme is slightly better than TVD scheme in resolving the flow structures.

1-D compressible two component flows are computed with a modified Level Set method where the Euler equations and Level Set equation are combined into a whole conservation law and are solved with high resolution finite difference schemes. In order to minimize the numerical oscillation near the fluid interface, the Ghost Fluid method is used together with the Isobaric Fix, and numerical results are presented for 1-D problems.

Under the condition of weak waveguiding, the effect of index gradual change is considered. The gradient index ∇ε as perturbation term is introduced in the scalar Helmholtzequation, and the perturbation method is used to solve the problem of triangular-profile gradient index single-mode fiber, which can shift the dispersion minimum from the wave length 1.31μm to 1.55μm. The first order correct solution is given with an integral form and numerical results calculated by integral expression are also given.

General formulae for propagating directions of the polarized light at the inner and external of biaxial crystal are obtained in the case that ray along arbitrary direction is incident upon a crystal of arbitrary making direction. The transition from it to uniaxial crystal, refractive rays lying in the incident plane and cone refraction are discussed. At last, the corresponding numerical results are plotted in curvilineal diagrams for Iceland spar and crystal sulphur, they make the directions of the refractrive rays clear as the crystal rotates. These results provide an important basis for study of new crystal optical components and new measuring methods of crystal optical constants.

A Scalar wave equation with an aix direction variate z is used to describe a single-mode taper fiber, and the scalar wave equation is changed to one-order differential equations group by a Simple transform. The quartic Runge-kutta Method improved by Gill is used to Calculate the propagation Characters of a Single-mode taper fiber.