束流传输管道孔径变化引起的束团场能差

Difference of Field Energy of a Bunched Beam Induced by Beam-Pipe Size Changes

由直线加速器提供的用于自由电子激光（ＦＥＬ）的电子束团，在其传输过程中常会遇到传输管道孔径变化的情况．本文在电荷密度均匀分布假定下，应用直线加速器中空间电荷束团的有限长柱模型，推导得到了束流传输管道孔径变化引起的束团场能变化及场能差公式．数值计算结果表明，它与国外以往所采用的以连续束流来代表直线加速器中电荷束团而得到的结果，有很大的差别，并且是更符合直线加速器中的电荷束团的实际情况，因而是更精确和可靠的．

A bunched beam for Free Electron Laser(FEL)driven by a linac always encounters some beam-pipe size changes in its transport process.In this paper,the formulae are derived for calculating the equilibrium field energy of a bunched beam and its difference in two pipe sizes by using a space charge cylinder model.The calculations show that a great difference between the results of space charge cylinder model and continuous beam model used before.