小有效发射度的各向异性磁准消色差材料
Anisomagnetic quasi-achromats with small effective emittance
摘要：
准消色差晶格（小的色散是允许在他们的直线部分，他们的细胞之间）被认为是在一个细胞，有两种不同的磁场的弯曲磁铁。有效发射度的最小化由以下算法（其遵循Teng，部分遵循Lee）执行。(1)每个内偶极子对自然发射度的贡献相对于所有光学参数最小（与色散和β函数有关），除了移位参数s_0，它规定了β函数最小值和磁体中心之间的间隔;对于侧弯曲磁体，其对与有效发射度相关的积分的贡献（该关系使用算术平均值优化几何平均值的事实）被最小化。(2)偶极子的其他参数（场、长度或角度比、位移）受边界条件的限制：在磁体出口处和下一个入口处Courant-Snyder不变量的相等。(3)通过计算可以找到最小有效发射度和最后自由参数（两个或三个）。这种方法的准确性下降的内部偶极子在一个细胞的数量减少，和仍然等磁Tanaka-Ando最小值（修改后的DBA*-晶格，没有内部偶极子）是再现精度优于百分之零点五。如果每个单元的偶极子的数量不超过四个，最小的有效发射度（14%，低于TA限制）是实现QBA**-晶格，其中所有的偶极子有非零位移。
英文摘要：
Quasi-achromat lattices (small dispersion is allowed in their straight sections, between their cells) are considered; in a cell, there are bending magnets of two kinds, of unequal magnetic field. Minimization of the effective emittance is carried out by the following algorithm (which follows Teng, and partly Lee). (1) Every inner dipole's contribution to the natural emittance is minimized with respect to all optics parameters (relating to dispersion and beta-function), except for the shift parameter, s_0, which specifies the interval between the beta-function minimum and the center of a magnet; for a side bending magnet, its contribution to an integral relating to the effective emittance (the relation uses the fact that the arithmetic mean majorizes the geometric mean) is minimized. (2) The other parameters of dipoles (fields, lengths or angles ratios, shifts) are restricted with the boundary conditions: the equality of Courant-Snyder invariants on the exit from a magnet and on the entrance to the following one. (3) The minimum of effective emittance and the last free parameters (two or three) can be found by computation. The accuracy of this method falls with decreasing of the number of internal dipoles in a cell, and still the isomagnetic Tanaka-Ando minimum (for the modified DBA*-lattice which has no inner dipoles) is reproduced with accuracy better than half a percent. If the number of dipoles per cell does not exceed four, the smallest effective emittance (14% lower than TA-limit) is achieved for QBA**-lattice where all dipoles have nonzero shifts.
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