电荷束团非均匀密度分布引起的发射度增长

EMITTANCE GROWTH CAUSED BY NONUNIFORM SPACE CHARGE DISTRIBUTIONS OF BUNCHED BEAM IN LINAC

直线加速器中电荷束团的非线性效应是导致束流发射度增长的一个重要原因。文中给出直线加速器中几种常见的非均匀密度分布的有限长空间电荷束团所具有的非线性自场能，即纵向非均匀电荷密度分布分别为水袋型、抛物线型，而横向密度分布为均匀（Ｋ－Ｖ）型、水袋型、抛物线型及高斯型等各种组合非均匀密度分布的自场能公式，并得到了由束团非线性均匀电荷密度分布引起的束流发射度增长。

The nonlinear space charge effect of bunched beam in linac is one of the important factors that induce the emittance growth due to the conversion of the field energy to kinetic energy. In the paper, using a cylinder model of space charge in linac, we derived the internal field energy for a bunched beam with some nonuniform space charge distributions, such as Gaussian, waterbag and parabolic distributions in both longitudinal and transverse directions. And the emittance growth caused by these nonuniformities is worked out.