Research On Three-dimensional Reconstruction Methods Of Asymmetric Plasma In ICF

In the research of inertial confinement fusion(ICF)diagnostic technology,the symmetry and homogeneity of the implosion in plasma’s compression has always been a difficult problem in the diagnosis,which also is one of the important preconditions for achieving fusion ignition.The traditional imaging diagnosis methods mainly analyze the two-dimensional picture information that captured in the experiment.However,this information only represents the average information,the three-dimensional distribution of important physical quantities cannot be obtained,and the accurate diagnosis of symmetry and uniformity in compression can not be achieved.The three-dimensional plasma reconstruction technology is an effective method to obtain the three-dimensional distribution of key parameters by using a small amount of X-ray pictures that took in implosion.With the plasma parameters,more important physical information can be obtained,such as the symmetry of compression,electron temperature,and electron density,which can provide important data support for ICF diagnostics and ignition design.Due to the limited conditions,only a few two-dimensional images can be got in the ICF.Besides,too many reconstruction parameters will lead to lower accuracy.The traditional method is generally based on the symmetric hypothesis for reconstruction,but the instability in the implosion process will make the plasma become asymmetrical structure.Therefore,this paper proposes a new asymmetric plasma three-dimensional reconstruction method which small number of reconstruction parameters are used to achieve accurately 3D reconstruction,and simulation verification analysis was performed.The main research contents of this paper are:1.The background of the three-dimensional reconstruction of ICF plasma and the principle of traditional three-dimensional reconstruction based on X-ray images are thoroughly studied.By analyzing the forward imaging process of plasma,a numerical simulation model of plasma under appropriate simplified conditions is established,which is a theoretical foundation of three-dimensional reconstruction.2.On the basis of traditional spherical symmetry model,a new asymmetric plasma three-dimensional reconstruction method is proposed,which combines the characteristics of plasma structure,including an asymmetric three-dimensionaldistribution model based on spherical harmonics and a genetic-least squares combined optimization algorithm,then the numerical simulation was implemented on MATLAB,and the influencing factors of reconstruction accuracy were analyzed and discussed.3.Based on the asymmetric 3D reconstruction method,the emission coefficient and the absorption coefficient are successfully reconstructed at the same time when radiation absorption is taken into consideration.The simulation results show that the accurate reconstruction achieved at low noise.Afterwards,the asymmetric three-dimensional reconstruction under complex multilevel can be further realized.It proved that this method not only can simulate the complex and asymmetrical plasma conditions,but also the reconstruction accuracy is high.