上海光源二期工程的垂直发射度研究

上海光源二期工程正在设计一个新的磁聚焦结构,它包含双斜插入件、超导二极铁以及超导扭摆器等新的元件。光谱亮度是表征同步辐射光源性能的一个重要参数,通过降低垂直发射度的方式来提高亮度是一种简便可行的方法。首先分别模拟和计算了各类磁铁准直误差对垂直发射度的影响,然后采用奇值分解法校正了误差引起的闭轨畸变,最后使用60个斜四极铁来校正垂直发射度。结果表明,在上海光源二期工程的磁铁准直公差与目前正在运行的上海光源相同的条件下,六极铁垂直准直误差对垂直发射度的影响最大;用60个斜四极铁来校正垂直发射度,能使耦合度保持在0.5%以下。

Study on the vertical emittance for the SSRF Phase II project

Background: The spectral brightness is an important parameter for the synchrotron radiation light source. It is intimately associated with beam current, horizontal emittance and vertical emittance. The beam current is limited by collective effects and the horizontal emittance is decided by the lattice structure, which has almost been fixed in a machine. Reducing the vertical emittance to improve the brightness is a simple and feasible method. Other benefits such as the increase of transverse coherence and the reduction of vertical spot size can be obtained in reducing the vertical emittance.Purpose: The aim is to study the sensitivity of the vertical emittance to magnetic alignment errors and correct the vertical emittance for the Shanghai Synchrotron Radiation Facility (SSRF) Phase II project.Methods: Singular values decomposition (SVD) is used to correct the vertical closed orbit distortion (COD). Sixty skew quadrupole magnets are utilized to correct the emittance coupling with gradient descent algorithm.Results: An approximate mean of 0.06-mm vertical COD is obtained after orbit correction. The emittance coupling of each seed can be corrected below 0.5% by using 60 skew quadrupole magnets.Conclusion: If the alignment tolerances of all magnets in the SSRF Phase II project are the same as those in the currently operational SSRF storage ring, the vertical emittance is primarily determined by vertical misalignments of the sextupole magnets, and the emittance coupling can be corrected below 0.5% by using 60 skew quadrupole magnets.