PEP-II高能环的小动量压缩因子晶格
Lattice with Smaller Momentum Compaction Factor for PEP-II High Energy Ring
摘要：
目前，PEP-Ⅱ束团长度和相互作用点（IP）处的垂直β函数的大小大致相同。为了增加亮度，计划逐步减少IP beta功能。为了获得最大的效果，还必须减小聚束长度，以最大限度地减少IP处沙漏效应引起的亮度损失。减小束团长度的方法之一是减小动量压缩因子。本文讨论了高能环的一种晶格方案，其中四个弧中的标称60度单元被90度单元取代，以减少30%的动量压缩因子和16%的束团长度。在90度单元中增加的聚焦由于减小的色散和较大的色度而导致40%更强的弧四极和150%更强的弧六极。跟踪模拟预测，该晶格的动态孔径将超过10倍的RMS大小的完全耦合光束的水平发射度为30 nm和IP β函数为1厘米。晶格修改和模拟结果。
英文摘要：
At present, the PEP-II bunch length and vertical beta function at the Interaction Point (IP) are about of the same size. To increase luminosity, it is planned to gradually reduce the IP beta function. For the maximum effect, bunch length has to be also reduced to minimize luminosity loss caused by the hourglass effect at IP. One of the methods to achieve a smaller bunch length is to reduce momentum compaction factor. This paper discusses a lattice option for the High Energy Ring, where the nominal 60 degree cells in four arcs are replaced by 90 degree cells to reduce momentum compaction factor by 30% and bunch length by 16%. The increased focusing in 90 degree cells results in 40% stronger arc quadrupoles and 150% stronger arc sextupoles due to reduced dispersion and larger chromaticity. Tracking simulations predict that dynamic aperture for this lattice will be more than 10 times the rms size of a fully coupled beam for a horizontal emittance of 30 nm and IP beta function of 1cm. The lattice modification and results of simulations are presented.
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