[论文解读] Ion Polarization Scheme for MEIC

A. M. Kondratenko, M. A. Kondratenko+5 more|arXiv (Cornell University)|Apr 19, 2016

Particle Accelerators and Free-Electron Lasers参考文献 12被引用 5

一句话总结

本文提出一种新颖的离子极化方案，用于中能电子-离子对撞机（MEIC），采用8字形环形拓扑结构，并利用弱螺线管控制自旋动力学。通过将自旋频率设为零而非1/2，该方案消除了弯曲段引起的自旋去极化，实现了通过低强度纵向磁场进行精确、非侵入式极化控制，大幅降低共振去极化效应，实现亚秒级自旋翻转。

ABSTRACT

The choice of a figure 8 shape for the booster and collider rings of MEIC opens wide possibilities for preservation of the ion polarization during beam acceleration as well as for control of the polarization at the collider's interaction points. As in the case of accelerators with Siberian snakes, the spin tune is energy independent but is equal to zero instead of one half. The figure-8 topology eliminates the effect of arcs on the spin motion. There appears a unique opportunity to control the polarization of any particle species including deuterons, using longitudinal fields of small integrated strength (weak solenoids). Contrary to existing schemes, using weak solenoids in figure-8 colliders, one can control the polarization at the interaction points without essentially any effect on the beam's orbital characteristics. A universal scheme for control of the polarization using weak solenoids provides an elegant solution to the problem of ion acceleration completely eliminating resonant beam depolarization. It allows one to easily adjust the polarization in any direction at any orbital location, which becomes necessary when transferring the beam from one ring into another or when measuring the polarization by polarimeters. It also allows for an easy manipulation of the spin direction at an interaction point during an experiment. The latter feature allows one to set up a spin-flipping system with a spin reversal time of less than a second. By compensating the coherent part of the zero-integer spin resonance strength, which arises due to errors in alignment of the magnetic element of the lattice, one can reduce the field integrals of the control solenoids by a few orders of magnitude.

研究动机与目标

• 解决在MEIC对撞机中加速过程中维持离子极化的问题。
• 消除由晶格错位和磁质错误引起的共振束流去极化。
• 实现在对撞点对离子自旋取向的灵活、实时控制，且不降低束流质量。
• 开发一种适用于多种离子种类（包括氘核）的通用极化控制方法。
• 通过补偿相干零整数自旋共振强度，降低控制螺线管所需磁场积分值。

提出的方法

• 采用8字形环形几何结构，将自旋运动与弯曲段效应解耦，确保自旋频率为零。
• 使用低磁场积分强度的弱螺线管控制自旋取向，而不影响轨道束流动力学。
• 通过晶格误差引起的零整数自旋共振强度抵消实现自旋频率补偿。
• 在任意轨道位置（包括环间束流传输期间）应用纵向磁场以操控自旋方向。
• 设计一种自旋翻转系统，利用受控螺线管磁场实现反转时间小于1秒。
• 采用通用方案，实现在加速器任意位置任意方向的极化调节。

实验结果

研究问题

• RQ1 8字形环形拓扑结构能否消除离子加速器中弯曲段引起的自旋去极化？
• RQ2 弱螺线管在多大程度上可实现对离子极化的控制，而对束流轨道特性影响极小？
• RQ3 通过补偿相干零整数自旋共振强度，能否有效降低所需螺线管磁场积分值？
• RQ4 能否在高能离子对撞机中利用该方案实现亚秒级自旋翻转？
• RQ5 所提出的方案是否普遍适用于多种离子种类，包括氘核？

主要发现

• 8字形拓扑结构可实现自旋频率为零，彻底消除弯曲段对自旋运动的影响。
• 弱螺线管可在对撞点实现极化控制，对束流轨道特性影响极小。
• 通过补偿相干零整数自旋共振强度，晶格误差引起的共振束流去极化显著降低。
• 通过共振补偿，控制螺线管所需磁场积分值降低了数个数量级。
• 利用该方案可实现反转时间小于1秒的自旋翻转。
• 该方法可在加速器任意位置实现对自旋取向的通用、灵活控制，方向任意。