Studying On The Diagnostic System And Nonlinear Reconstruction Methods For Neutron Penumbral Imaging In Inertial Confinement Fusion

The energy problem is more and more important while the human develop forward.The luxuriant and clean energy from controlled nuclear fusion is concerned extensively in order to solve this crisis. Magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) that has been studying are the most possible ways to control nuclear fusion. Now, laser-driven inertial confinement fusion is availability in experiment, the fuel target is heated and compressed into high temperature and high density in the short time by high powerful laser, then the fuel is ignited and the controlled nuclear fusion becomes true.For decreasing the driving energy, the high contraction ratio is necessary in the compressing in laser-driven inertial confinement fusion, and high symmetry what is less than 1% is needed in the radiation drive. If the driving symmetry cannot be satisfied, the kinetic energy that is used to impresses the fuel cannot be transformed into internal energy of the fuel, and hydrodynamics instabilities will become more and more serious, the ignition and the burning will be weakened, even lead failure.So it is necessary to invent high-resolution equipment to diagnose the temporal and spatial behaviors of the target. Neutron penumbral imaging is an important technique to diagnose the hydrodynamics instabilities and the symmetry in the compressing in inertial confinement fusion experiment,In order to refine the resolution of 5μm,it is necessary to study the diagnosing system and the nonlinear reconstruction methods, so we have done some significant work in this paper.First of all, we simply introduce some basic concepts of ICF, the history of research, the methods of diagnosing, and the advantages of neutron penumbral imaging. We also keep emphases on the principle of the penumbral imaging, equipments, history of diagnosing, and some reconstruction methods, including the linear methods of wiener and the filtered autocorrelation, the nonlinear methods of tabu search, genetic algorithm and molecular dynamics. Then the MC method that is used to calculate the neutron penumbral imaging is shown.Seconds, we detailed simulate the point spread function (PSF) in order to optimize the diagnosing system. The diagnosing system is optimized base on the sharpness and isoplanaticity of PSF, and we get some interesting result:source-aperture distance is 9cm, aperture-detector distance is 9m, thickness of biconical aperture is 5cm and outer radius is 0.5cm. According to the simulation, misalignment acceptance of system is analyzed. And the resolution of system is introduced by theory and testing.Thirds, the effect of scattered neutron in neutron penumbral imaging is calculated by simulating the experimental environment in ICF.We can make the conclusions that the effect of scattered neutron can be ignored. We also simulate the energy depositing of neutron in detector with deuterated scintillator by MC method, and demonstrate the linear relation between energy depositing of the neutron with surface flux.Finally, we do some jobs in the nonlinear reconstruction of neutron penumbral imaging. We improve the molecular dynamics method, by using the Leap-frog format to increase convergence, and adding the edge-preserving regularization to depress the edge-diffusion. Furthermore, the conjugate gradient method is also studied, and the relationship and differences between two methods are revealed. The statistic reconstruction is studied too.In the paper, all the work, including the system optimizing of neutron penumbral imaging, the analyzing of the fabrication error,resolution and the scattered neutron, and the discussing of reconstruction methods, can be used to improve the diagnosing experiment and decode. The spatial resolution of 5μm can be absolutely satisfied neutron penumbral imaging in ICF.