储存环中自旋相干与退相干的几种模型
Some models of spin coherence and decoherence in storage rings
摘要：
本文提出了储存环中同步辐射噪声引起的自旋扩散的几个简单的精确可解模型。我能够使用标准的随机微分方程和福克-普朗克方法，从而引入并利用极化密度。这个量服从布洛赫型的线性演化方程，它和福克-普朗克方程一样，在与系统状态无关的意义上是普适的。我也简要地考虑布洛赫方程的其他本地偏振量来自偏振密度。所选择的模型之一是相关的一些现有的和拟议的低能量电子（正电子）存储环，需要极化。我提出了一个环的HERA的典型参数的数值结果，并表明，在适用的情况下，我的方法的结果是令人满意的协议与使用SLIM计算。这些计算提供了使用n轴计算去偏振的常规方法的基本原理的数值检查。我还调查了自旋系综的平衡行为时，没有同步辐射。最后，我总结了我用偏振密度得到的其他结果，这些结果将单独发表。
英文摘要：
I present some simple exactly solvable models of spin diffusion caused by synchrotron radiation noise in storage rings. I am able to use standard stochastic differential equation and Fokker-Planck methods and I thereby introduce, and exploit, the polarization density. This quantity obeys a linear evolution equation of the Bloch type, which is, like the Fokker-Planck equation, universal in the sense that it is independent of the state of the system. I also briefly consider Bloch equations for other local polarization quantities derived from the polarization density. One of the models chosen is of relevance for some existing and proposed low energy electron (positron) storage rings which need polarization. I present numerical results for a ring with parameters typical of HERA and show that, where applicable, the results of my approach are in satisfactory agreement with calculations using SLIM. These calculations provide a numerical check of a basic tenet of the conventional method of calculating depolarization using the n-axis. I also investigate the equilibrium behaviour of the spin ensemble when there is no synchrotron radiation. Finally, I summarize other results which I have obtained using the polarization density and which will be published separately.
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