Emittance minimisation with longitudinal dipole field variation
Emittance minimisation with longitudinal dipole field variation
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DOI：
10.1016/j.nima.2007.02.086
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发表时间：
2007-06
影响因子：
1.4
通讯作者：
R. Nagaoka;A. Wrulich
中科院分区：
文献类型：
--
作者：
R. Nagaoka;A. Wrulich
通过在弯曲磁体中引入磁场的纵向变化，可以使水平发射度降低到常规极限之外。对于给定的偶极子场，在不同的边界条件下，从光源环优选的消色差条件出发，解析地表达了最小发射度的搜索。当偶极子场沿纵向位置快速衰减时，发射度可以进一步降低，这主要是通过使H函数与局部曲率的三次方失相来实现的。在解析得到的最小发射度条件下，用多项式函数对最优偶极子场分布进行数值搜索，同时分析了降低发射度的机理。最小发射度是所需峰场和场分布的函数。本文还讨论了标准磁体晶格中纵向变化的偶极子场对光源的适应性。
The reduction of horizontal emittance beyond the conventional limit is pursued by introducing a longitudinal variation of the field in a bending magnet. For a given dipole field, the search for the minimal emittance is formulated analytically under different boundary conditions, starting from the achromat condition, preferred for light source rings. With a dipole field rapidly decaying along the longitudinal position, it is shown that the emittance can be further reduced, essentially by rendering the H function to be out of phase with the third power of the local curvature. Under the minimal emittance condition analytically obtained, the optimal dipole field distribution is searched numerically with a polynomial function, analysing at the same time the mechanism of the emittance reduction. The minimal emittance is argued as a function of the required peak field and the field distribution. Adaptability of longitudinally varying dipole fields in a standard magnet lattice for light sources is also addressed.