Kim Eun-San
Department of Physics, Kyungpook National University, Sangyok-dong, Bukgu, Daegu 702-701, Republic of Korea.
Rev Sci Instrum. 2010 Oct;81(10):103301. doi: 10.1063/1.3488362.
The Pohang Light Source (PLS) storage ring is a synchrotron light source with the emittance of 18.9 nm at 2.5 GeV and has delivered vacuum ultraviolet and soft x-rays during the past 15 years. We investigate a lattice design for the 3 GeV ring for an upgrade project that keeps the existing tunnel. We investigate a double bend achromat (DBA) structure that provides the reduction of emittance by a factor of 3 and the increase of the number of straight section by a factor of 2 than the existing PLS lattice. We present several characteristics on the beam dynamics, dynamic aperture, and optics matching in the low-emittance lattice which includes squeezed space between magnets. Present PLS lattice has 12 long straight sections of 6.8 m long and the lattice is modified to provide the additional 12 short straight sections of 3.7 m long by eliminating a bending magnet in the middle of the cell of the present triplet bending achromat lattice. Thus, the new lattice consists of a total of 24 straight sections that consist of 12×6.8 and 12×3.7 m long straight sections, which can provide the spaces for the 4- and 2-m-long insertion devices. We present the design results in detail for a DBA lattice in 281.82 m long circumference. It is shown that the emittance of 6.2 nm in the lattice can be achieved by allowing nonzero dispersions in the straight sections. The lattice provides high brilliance at the photon energy of a few 10 keV that meets the requirements by synchrotron radiation users; however, it may require a strong focusing and become sensitive to machine errors and effects of insertion devices. Thus, we investigated the dynamic aperture in the lattice by a simulation method and achieved an optimal tune under the strength of sextupole magnets of 500 T/m(2) for the low-emittance ring. We also performed the lattice tunings to restore the optics due to the errors in the low-emittance ring. In result, our designed lattice shows a good optimization in terms of emittance, brilliance, and circumference as a light source for a 3 GeV.
浦项光源（PLS）储存环是一台同步辐射光源，在2.5 GeV时发射度为18.9 nm，在过去15年中一直提供真空紫外光和软X射线。我们为一个升级项目研究了用于3 GeV环的晶格设计，该项目保留现有隧道。我们研究了一种双弯消色差（DBA）结构，与现有的PLS晶格相比，它能将发射度降低至三分之一，并将直线节数量增加一倍。我们展示了低发射度晶格中束流动力学、动态孔径和光学匹配的几个特性，其中包括磁铁之间的压缩空间。现有的PLS晶格有12个6.8 m长的长直线节，通过消除当前三联弯消色差晶格单元中间的一个弯曲磁铁，对晶格进行修改以提供另外12个3.7 m长的短直线节。因此，新晶格共有24个直线节，由12个6.8 m长和12个3.7 m长的直线节组成，可为4 m和2 m长的插入装置提供空间。我们详细展示了周长为281.82 m的DBA晶格的设计结果。结果表明，通过在直线节中允许非零色散，可在晶格中实现6.2 nm的发射度。该晶格在几十keV的光子能量下提供高亮度，满足同步辐射用户的要求；然而，它可能需要强聚焦，并且对机器误差和插入装置的影响变得敏感。因此，我们通过模拟方法研究了晶格中的动态孔径，并在低发射度环的六极磁铁强度为500 T/m²的情况下实现了最佳调谐。我们还对低发射度环中的误差进行了晶格调谐以恢复光学性能。结果，我们设计的晶格作为3 GeV的光源，在发射度、亮度和周长方面显示出良好的优化。
