螺线管透镜像差导致的束流发射度增长研究

螺线管透镜常作为低能束流的聚焦元件，不可避免地具有像差，导致束流发射度增长,降低束流传输效率。本文通过理论推导和计算机模拟，给出了不同束流包络、不同磁感应强度和不同磁场形状的情况下束流经过实际透镜后的发射度增长。结果表明，发射度增长主要与束流包络和磁感应强度有关。但在一定范围内，优化磁场形状也能起到控制发射度增长的作用。

Study on Beam Emittance Growth Induced by Spherical Aberration of Solenoid Lens

The solenoid lens are effective for focusing the low energy beam, but the beam efficiency decreases with the beam emittance growth, which increases with the spherical aberration of solenoid lens. Emittance growth due to spherical aberration of solenoid lens was studied in both theory and simulation in this paper. The results show that emittance growth is mainly dominated by the beam envelope in lens and magnetic strength of lens. Optimizing the magnetic field uniformity of solenoid lens, which decides the aberration coefficient, can reduce the spherical aberration and enhance the quality of beam to an extent.