PIC方法在RFQ加速器z-code和t-code模拟程序中的应用研究

Application of PIC method for z-code and t-code simulation in RFQ accelerators

本文介绍了二维PIC(Particle in cell)方法,这种方法常用于粒子动力学模拟中空间电荷作用的计算。并比较了以时间为自变量(t-code)和以纵向位置为自变量(z-code)的两种动力学模拟程序;针对“国家重点基础研究发展规划”洁净核能项目中的射频四极(RFQ)加速器结构参数,给出了单束加速和正、负离子束同时加速两种情况下,t-code和z-code模拟得出的传输效率。结果表明,当束团的相位宽度大或能散大时,z-code 在计算空间电荷作用时会引入相对较大的误差,从而应该使用t-code来进行动力学模拟,以获得更准确的结果。

The 2D PIC (Particle in cell) method, widely used in the calculation of space charge effect for particle dynamic simulations is described. The difference between t-code (Using time as independent variable) and z-code (Using longitudinal position as independent variable) is illuminated. For single beam acceleration and positive-negative ion beams acceleration, simulation results of the transmission rate using t-code and z-code are provided, respectively, with the structure parameters of the RFQ (Radio frequency quadrupole) accelerator in the Clean Nuclear Power Project of Major State Basic Research Development Program. The results show that when the phase spread or energy spread of the bunch is large, relatively large errors could be introduced in z-code during the calculation of space charge effect. Therefore t-code should be adopted instead in the dynamic simulations for more accurate results.