CSNS/LRBT优化设计及空间电荷效应影响研究

中国散裂中子源（CSNS）直线加速器至快循环同步加速器（RCS）的束流输运线（LRBT）传输80 MeV H^-束流至RCS注入点，由于较小的束流发射度和较高的峰值流强，空间电荷效应在LRBT中的影响非常显著，是引起LRBT中发射度增长和束流损失的主要因素，也是LRBT优化设计中的重要问题。文章利用TRACE 3-D程序进行带有空间电荷效应的twiss参量和消色散匹配，比较研究LRBT不同聚焦结构和不同初始束流分布条件下发射度的增长情况。对于采用Triplet结构作为标准单元的结构，研究发现，通过优化LRBT前端匹配段能有效控制发射度的增长。多粒子模拟跟踪结果表明，峰值流强为15 mA时，现有物理孔径下基本无束流损失发生。对LRBT上散束器的参数和位置进行了优化设计，可减少动量散度和中心能量抖动，优化RCS注入束流参数。

Space Charge Effects Study and Optimization in CSNS/LRBT

The LINAC to ring beam transport line (LRBT) of China Spallation Neutron Source (CSNS) connecting the LINAC and the rapid cycling synchrotron (RCS) transports 80 MeV H^- beams for RCS injection. Effects of space charge of the beam in LRBT due to small emittance and high current is a major cause of emittance growth and beam loss and therefore become important issues in the LRBT design. An achromatic transverse optical matching was operated by Trace 3-D code. Emittance growths of beams with different initial distributions in several LRBT lattices were studied separately. Simulation results show that the LRBT design with Triplet can mitigate the emittance growth by adjusting the lattice of the front matching part and no beam loss occurs at 15 mA. The location and parameters of the debuncher in LRBT were also optimized to reduce the momentum spread and energy jitter.