轴对称平板二极管空间电荷限制流的2维效应
Two-dimensional geometry effect on space-charge-limited current in axially symmetrical planar diode
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摘要: 应用精度较高的体积加权电荷、电流分配模型，对轴对称平板二极管的空间电荷限制流2维效应进行了粒子模拟研究。选取电压分别为100 kV和1 MV两种情况，对空间电荷限制流受二极管尺寸影响的规律进行了模拟。模拟结果表明，2维效应使空间电荷限制流密度随二极管形状因子(阴极发射半径与阴阳极间隙的比值)的减小而增大，且受相对论效应的影响不明显。经数值拟合得到了空间电荷限制流2维效应与形状因子相关的二阶经验公式，其一阶系数与一阶理论结果基本一致，约为1/4。Abstract: Two-dimensional (2-D) geometry effect on space-charge-limited(SCL) current of an axially symmetrical planar diode was studied with 2.5 D particle-in-cell(PIC) simulation. A volume-weighting cloud-in-cell model was used to improve the accuracy of the PIC method in z-r coordinates system. The simulations with various emitter radii were carried out on the same diode with the applied voltages being 100 kV and 1 MV respectively. The simulation results show that the 2-D geometry effect on SCL current monotonically diminishes with the dimensionless ratio of emitter radius to gap separation, whether in relativistic or non-relativistic regime. When the ratio is more than 0.5, the first-order analytical theory well predicts the limiting current. But when the ratio is no more than 0.5, the second-ord
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