Beam loss reduction by magnetic shielding using beam pipes and bellows of soft magnetic materials
Beam loss reduction by magnetic shielding using beam pipes and bellows of soft magnetic materials
复制标题
使用软磁材料的束管和波纹管通过磁屏蔽减少束损耗
DOI：
10.1016/j.nima.2014.06.062
复制
发表时间：
2014
影响因子：
1.4
通讯作者：
M. Kinsho
中科院分区：
文献类型：
--
作者：
J. Kamiya;N. Ogiwara;H. Hotchi;N. Hayashi;M. Kinsho
高功率加速器中束流损失的主要来源之一是束流线附近的磁体产生的不需要的杂散磁场，这可能会扭曲束流轨道。屏蔽此类磁场的最有效方法是用软磁高磁导率材料完美地包围光束区域，没有任何间隙。这导致了用软磁材料制造真空室（束管和波纹管）。管道部件和外部波纹管部件的材料选用镍铁合金（坡莫合金），法兰选用铁素体不锈钢。内部波纹管采用非磁性材料奥氏体不锈钢，以实现真空密封。为了获得良好的磁屏蔽和真空性能，在真空室的制造过程中采用了高真空热处理。通过该热处理，束流管和波纹管的内侧和外侧之间沿束流轨道的积分磁通密度之比变得足够小，足以抑制束流轨道畸变。经过这种热处理的材料的脱气率比未经热处理的材料降低了一个数量级。通过在日本质子加速器研究综合体 3 GeV 快速循环同步加速器束流线中安装软磁材料束管和波纹管，闭轨畸变 (COD) 减少了 80% 以上。此外，COD 的改善还实现了 95.5% 的光束存活率。
One of the main sources of beam loss in high power accelerators is unwanted stray magnetic fields from magnets near the beam line, which can distort the beam orbit. The most effective way to shield such magnetic fields is to perfectly surround the beam region without any gaps with a soft magnetic high permeability material. This leads to the manufacture of vacuum chambers (beam pipes and bellows) with soft magnetic materials. A Ni–Fe alloy (permalloy) was selected for the material of the pipe parts and outer bellows parts, while a ferritic stainless steel was selected for the flanges. An austenitic stainless steel, which is non-magnetic material, was used for the inner bellows for vacuum tightness. To achieve good magnetic shielding and vacuum performances, a heat treatment under high vacuum was applied during the manufacturing process of the vacuum chambers. Using this heat treatment, the ratio of the integrated magnetic flux density along the beam orbit between the inside and outside of the beam pipe and bellows became small enough to suppress beam orbit distortion. The outgassing rate of the materials with this heat treatment was reduced by one order magnitude compared to that without heat treatment. By installing the beam pipes and bellows of soft magnetic materials as part of the Japan Proton Accelerator Research Complex 3 GeV rapid cycling synchrotron beam line, the closed orbit distortion (COD) was reduced by more than 80%. In addition, a 95.5% beam survival ratio was achieved by this COD improvement.