极化质子加速的Siberian Snakes最佳轴
Optimal Axes of Siberian Snakes for Polarized Proton Acceleration
摘要：
加速极化质子束并将其存储多圈可导致在通过自旋旋转频率与轨道振荡频率共振的能量加速时极化的损失。一阶共振效应可以通过在环中安装西伯利亚蛇来避免，这些装置可以使自旋绕蛇轴旋转180度，同时不会显著改变光束的轨道。对于大型戒指，需要几条西伯利亚蛇。这里将导出一个标准，允许找到蛇轴的最佳选择。对超周期四的环进行了详细的分析，并以HERA质子环为例进行了近似四重对称性的研究。我们提出的西伯利亚蛇的排列方式与它们的效应相匹配，使得所有的自旋轨道耦合积分在所有能量下都为零，因此对于这种选择，根本不存在一阶自旋轨道耦合，我称之为蛇匹配。它将表明，在一般情况下，至少需要八个西伯利亚蛇，并有确切的四种可能性，以安排他们的轴。当电子感应加速器的相位超前选择适当时，四条西伯利亚蛇就足够了。为了表明已经发现了对蛇有利的选择，在HERA-p的加速周期的一部分中跟踪极化质子，这表明对于这里提出的西伯利亚蛇的排列，极化被最好地保留。
英文摘要：
Accelerating polarized proton beams and storing them for many turns can lead to a loss of polarization when accelerating through energies where a spin rotation frequency is in resonance with orbit oscillation frequencies. First-order resonance effects can be avoided by installing Siberian Snakes in the ring, devices which rotate the spin by 180 degrees around the snake axis while not changing the beam's orbit significantly. For large rings, several Siberian Snakes are required. Here a criterion will be derived that allows to find an optimal choice of the snake axes. Rings with super-period four are analyzed in detail, and the HERA proton ring is used as an example for approximate four-fold symmetry. The proposed arrangement of Siberian Snakes matches their effects so that all spin-orbit coupling integrals vanish at all energies and therefore there is no first-order spin-orbit coupling at all for this choice, which I call snakes matching. It will be shown that in general at least eight Siberian Snakes are needed and that there are exactly four possibilities to arrange their axes. When the betatron phase advance between snakes is chosen suitably, four Siberian Snakes can be sufficient. To show that favorable choice of snakes have been found, polarized protons are tracked for part of HERA-p's acceleration cycle which shows that polarization is preserved best for the here proposed arrangement of Siberian Snakes.
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