Studies of the aperture design and its pointing precision in fast neutron penumbral imaging

Neutron penumbral imaging technique is an important diagnosis method in Inertial Confined Fusion, and the design of the aperture shape will affect the resolution of the imaging system. In this paper, several designs of the aperture shape are discussed. Moreover, the pointing precision is also discussed, and a rational pointing precision is given.     

中子半影成像的数值模拟

 半影成像具有灵敏度高的特点，该技术是未来惯性约束聚变（ICF）中子成像的主要技术路线。基于中子半影成像的基本要求，利用蒙特卡罗方法，采用偏移抽样法和面通量的体通量替代技巧，模拟中子在半影成像系统中的输运，得到2维图像，并通过图像重建程序得到重建的源区图像。利用模拟结果，对编码孔屏蔽材料的选择和外径设计进行了初步优化，最终选择5 cm厚的钨屏蔽材料，其编码孔外径为1 cm。     

Application of Galerkin spectral method for tearing mode instability

Magnetic reconnection and tearing mode instability play a critical role in many physical processes. The application of Galerkin spectral method for tearing mode instability in two-dimensional geometry is investigated in this paper. A resistive magnetohydrodynamic code is developed, by the Galerkin spectral method both in the periodic and aperiodic directions. Spectral schemes are provided for global modes and local modes. Mode structures, resistivity scaling, convergence and stability of tearing modes are discussed. The effectiveness of the code is demonstrated, and the computational results are compared with the results using Galerkin spectral method only in the periodic direction. The numerical results show that the code using Galerkin spectral method individually allows larger time step in global and local modes simulations, and has better convergence in global modes simulations.     

中子半影成像图像反演方法研究

 给出了中子半影成像技术的原理；分析了系统分辨率的影响因子；利用MCNP软件对中子半影成像过程进行模拟；用改进的逆滤波和维纳滤波两种方法对成像主轴上一点源和偏轴两点源的编码图像进行重建，并对编码像在降低噪声和去除本底前后的反演结果进行了比较。模拟结果表明维纳滤波法能够更好地抑制统计噪声。