水平折叠式串列加速器是用来产生高能离子的装置,如图是其主体原理侧视图.图中

为一级真空加速管,中部

处有很高的正电势

,

、

两端口均有电极接地(电势为零);

、

左边为方向垂直纸面向里的匀强磁场;

为二级真空加速管,其中

处有很低的负电势

,

、

两端口均有电极接地(电势为零).有一离子源持续不断地向

端口释放质量为m、电荷量为e的负一价离子,离子初速度为零,均匀分布在

端口圆面上.离子从静止开始加速到达

处时可被设在该处的特殊装置将其电子剥离,成为正二价离子(电子被剥离过程中离子速度大小不变);这些正二价离子从

端口垂直磁场方向进入匀强磁场,全部返回

端口继续加速到达

处时可被设在该处的特殊装置对其添加电子,成为负一价离子(电子添加过程中离子速度大小不变),接着继续加速获得更高能量的离子.已知

端口、

端口、

端口、

端口直径均为L,

与

相距为2L,不考虑离子运动过程中受到的重力,不考虑离子在剥离电子和添加电子过程中质量的变化,

,

,求: