线型离子阱中空间电荷效应的理论分析

Theoretical analysis of the space charge effect in linear ion trap

线型离子阱中的离子在射频场作用下做宏观的久期运动,久期运动频率与实验参数有关.但当离子阱中囚禁大量同种电荷的离子时,空间电荷效应会导致离子间存在相互排斥的库仑力,使离子的运动频率发生漂移.本文通过求解泊松方程计算了空间电荷产生的附加电场的解析表达式,在小振动近似下理论计算了该附加电场对久期运动频率的影响,模拟了不同离子云中心密度下久期频率的漂移,讨论了离子云的数目、温度与实验参数之间的关系.对用离子阱进行的频标实验、碰撞实验和其他方面的研究都具有重要的指导意义.

An ion trapped in the linear ion trap will undergo secular motion with special frequency related to the radio frequency field.With increasing number of ions in the trap,space charge effect will cause Coulomb force between ions and result in motion frequency shift.In this paper,we use Possion’s equation to solve the extra electric field due to space charge and discuss the effect of this electric field on ion motion frequency.In the end,we also discuss the relationships between ion clouds numbers,ion clouds temperature and experimental parameters.All this work would be meaningful in frequency standards ion experiments as well as collision research.