电子束发射度变化的解析估计

ANALYTIC ESTIMATION FOR THE BEAM EMITTANCE CHANGE

本文使用一般包络方程理论推导出轴对称电子束在傍轴近似下的稳态传输过程中的发射度变化公式。结果表明电子束发射度变化与引导磁场及离子通道电场无直接关系,而仅仅与电子束分布的变化有关;发射度变化的本质是电子束的静电势能和横向运动的动能之间的转换。本文的解析结果与数值模拟结果符合得相当好。本文还定性讨论了电子束平均正则角动量对发射度变化的影响。

In this paper, the expression descrbing the change of emittance for an axisymmetic electron beam in the case of stationary transportis derived with the general envelope equation presented in Ref . ( 1 ) . The result suggests that the emittance change of a beam does not directly depend on the guiding magnetic field and the electrostatic field of the ion channel .but on the chang of the beam electron distribution . The cmittance change is essentially the consequnce of transferring between the space charge potential energy and the transveres effective thermal kinetic energy of the beam . The analytic results arc consistent with simulation very well . the effect of the canonical angular momentum on the beam emittance is qualitatively discussed .