一、引言众所周知,由两个极性相反的四极透镜所组成的双合透镜以及由三个极性相互交替的四极透镜所组成的三合透镜系统,可以在两个方向上实现聚焦,它们常常被用来聚焦束流或实现束流横向相空间的匹配。由于双合透镜在结构上比三合透镜简单,在束流输运系统中,一般多采用双合透镜系统。但是,三合透镜在x,y两方向较对称,如果要求所设计 I. INTRODUCTION It is well known that the double lens composed of two quadrupole lenses with opposite polarity and the triple lens system composed of three quadrupole lenses with alternating polarities can realize focusing in two directions, They are often used to focus the beam or to achieve a match in the lateral phase space of the beam. Because the double lens is simpler in structure than the triplet lens, the double-lens system is usually used in the beam transport system. However, the triplet is more symmetrical in the x and y directions, if required