Optical Path Tracing Method Of Laser Energy Deposition And Its Parallelization

In order to simulate the energy deposition in inertial confinement fusion droved by laser, a geometric optics approximation called the ray-tracing algorithm was used in general without solving Maxwell's equations. In the algorithm, laser beams are discretized into a lot of rays, which are initialized with certain energy. Each ray is followed until it is absorbed or leaves the physical domain; energy of ray is transferred to the mesh by inverse bremsstrahlung. The practical problems applying the ray-tracing algorithm are discussed in this paper.Firstly, the ray-tracing algorithm is presented, the key problems that need to be solved is analyzed, equations for ray trajectories, energy deposition and the power of laser pulse are described. Numerical calculation in 2-D Cartisien and 2-D cylindrical geometry is discussed.Secondly, some improvement is realized in the module of laser deposition, for instance, the method to calculate density of electron number is changed to bilinear interpolation. A new model of ray trajectory in vacuum is added, which is consistent with trajectory in plasma. On the same time, for simulation of X-ray laser generated by laser, focus-line model is added as well.With all work mentioned above, we have developed a new laser deposition module, which separate the complexities of the geometrical-optical ray-tracing problem from the basic physics modules. A 3D ray trajectory through a cell with an arbitrary direction is more accurately calculated and numerical precision is improved. When the interface about date I/O is designed, ray trajectories are rendered in 2-D and 3-D perspective with graphic tools that the result of numerical simulations is conveniently analyzed. The module has been used to the research and works well.Because of the requirements of large scale and highly efficient simulation, the parallelization of ray-tracing algorithm is described. Ray-tracing computation combined with the existing decomposition of the domain is effectively dealt with by the group-pipeline strategy. The code was designed with the message passing programming environment, can significantly improve the parallel performance. The numerical results show that computing efficiency of large scale increased above 30 percent against the ungroup-pipeline strategy.