高能同步辐射光源插入件永磁体辐照退磁分析

Irradiation demagnetization of permanent magnets in insertion device for high-energy synchrotron radiation light source

Nd2Fe14B永磁体是高能同步辐射光源插入件的核心构件,永磁体在高能电子加速器的混合辐射场中可能产生退磁的现象是高能同步辐射光源的一个重要问题。本文采用蒙特卡罗软件FLUKA模拟分析了Spring-8的电子直射Nd2Fe14B磁阵列的辐照损伤实验,建立了Nd2Fe14B磁阵列辐照剂量和退磁的关系。使用高能同步辐射光源(High Energy Photon Source,HEPS)波荡器插入件模型和恒流注入模式束流损失参数,计算了各个磁极受到的吸收剂量分布,分析了HEPS光束线站波荡器插入件的退磁情况。计算结果表明:插入件永磁体的退磁现象在入口处比较严重;插入件受到辐照剂量和束流损失的方式有很大关系,在52.5 nC电子直射损失在插入件入口、25.5 nC电子均匀损失在极板间隙的情况下,受辐照最严重的磁极运行2.1 a的辐照退磁可以达到5%,如果直射损失部分电子的比例变小,插入件的寿命会有一定程度的提高;在插入件入口处放置一定厚度的屏蔽材料或者增大极板间隙,能有效降低插入件内的吸收剂量。

[Background]In synchrotron radiation facilities,the insertion devices are installed on the storage ring to produce high brightness,high coherence,and adjustable polarization synchrotron radiation,which are composed of periodic permanent magnet arrays.The permanent magnets are continuously exposed to beam loss electrons due to the Touschek effect.As a result,the permanent magnets can be more or less damaged and deteriorates the magnetic field of insertion devices.Radiation-induced demagnetization of permanent magnets in the insertion device is one of the critical issues for synchrotron radiation facilities.[Purpose]This study aims to simulate the irradiation field and radiation damage of the Nd2Fe14B permanent magnet insertion devices during the routine operation of the high energy photon source(HEPS).[Methods]First of all,Monte Carlo code FLUKA was utilized to calculate the relationship between the absorbed dose and demagnetization of Nd2Fe14B magnet array based on the Spring-8 experiment.Then the different electronic sampling modes were set to calculate the irradiation field in the insertion device according to the actual beam loss conditions at HEPS.Finally,the demagnetization and countermeasures were analyzed according to the spatial distribution of absorbed dose.[Results]When HEPS works in top-up mode,the irradiation of the magnetic pole in the upstream end of the insertion device is more severe.Most of the absorbed dose(about 99.7%)is contributed by photon,electron and positron.According to the beam loss parameters by physical calculation,the expected life of the insertion device is 2.1 to 4.6 years.[Conclusions]Placing local shielding layer and increasing the gap are the effective measures to protect the insertion devices,hence slow down radiation demagnetization of permanent magnet.