Research On Radiation Symmetry Evaluation In Inertial Confinement Fusion Based On Compressive Sensing

The indirect-laser-driven Inertial Confinement Fusion(ICF) is the most promising approach to actualize the controlled thermonuclear reaction on earth. The radiation symmetry of target is a crucial task for the initiation of ICF experiment.. In this paper, a simulation experiment is conducted on the implosive and compressive process of the fuel target to compute the radiation symmetry rapidly and precisely. And then exercise optimization design on the parameters of the capsule and target based on the radiation symmetry, which will provide valuable advice for the real ICF experiment.Target surface radiation flux distribution is the premise of symmetry analysis. A time varying energy balance model is built by studying the radiation relationship between the capsule and target. A discrete view factor method is used to solve the radiation flux balance equations, which is high-nonlinear and large-scaled. The traditional method is iterative method, which turns out to be very slow and restricted by the equation scale.The Compressive Sensing theory tells us that a sparse signal can be reconstructed precisely by a few random samples with certain recovery algorithm. In this thesis, we analyzed the sparsity of radiation flux on the target in the spherical harmonic domain through massive numerical experiments. Then a weighting matrix is introduced to form a sampling matrix which is irrelevant to the basis matrix in order to satisfy the restricted isometry property(RIP) of measure matrix. Spherical random-measureing method is used to sample a few infinitesimals, where the radiation flux balance equation is built. The nonlinear compressive sensing can be solved by using Normalized Iterative Hard Thresholding(NIHT). Whereas, the NIHT method is very slow and unstable. Therefore, a new method named Conjugate Gradient Normalized Iterative Hard Thres-holding(CG-NIHT) is proposed combining Conjugate Gradient pursuit. The whole frame for using compressive sensing to compute radiation symmetry is built based on the new method.The stability and validation of the new method is validated through massive numerical simulation experiment. The CG-NIHT method is stable as well as precise. Compared with traditional method, the experiment results indicate that the CS method can save massive memory, improve the convergence rate, and the solving scales increase greatly.The CS based method is used in the ICF simulation software Irad3 D which is developed by our library, and a typical example of radiation symmetry computation for the Shen-GuangIII device is given out.