用Monte Carlo法模拟计算液态金属离子源的发射特性

本文运用Monte Carlo方法模拟计算液态金属离子源的发射特性.通过随机抽样确定离子发射的初始位置和速度,考虑离散的空间电荷效应,用四阶自动变步长Runge-Kutta方法计算离子的运动轨迹。为加速Poisson场收敛,本文用恒定的总束流进行每轮迭代,并提出以维持总发射束流恒定所需引出电压的变化作为衡量Poisson场收敛的判据。通过对大量离子的统计计算,获得了角电流强度、虚源的大小和位置、离子束能量散度和束斑大小等离子源的特性参量。

A MONTE CARLO CALCULATION OF ION EMISSION SYSTEM WITH A LIQUID METAL ION SOURCE

The emission characteristics of liquid metal ion source are simulated by Monte Carlo method. The initial positions and velocities of emitted ions are given by random sampling with random numbers. Trajectory calculations including the effect of discrete space charge are carried out with fourth order auto-variable-step Runge-Kutta method. In order to accelerate the convergence of Poisson field, the total emission current is kept constant in the iterative process, and we assume the quantity of voltage variation between two succesive iterations as the iterion of convergence. Finally, the emission characteristics of the ion source such as angular current intensity, energy spread, beam divergence, virtual source size and its position are given.