Preliminary study on in-situ activation of NEG coated vacuum chamber
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摘要: 合肥先进光源（HALF）是一台正在规划中的衍射极限同步辐射光源，其紧凑的物理设计和小孔径磁铁导致传统离散分布的真空泵系统很难达到衍射极限储存环所需的超高真空环境。镀有NEG（Non-Evaporable Getter）薄膜的小孔径真空盒不仅节约空间，还具有分布式吸气的能力，能满足衍射极限装置对超高真空的需求。NEG膜层需要在一定温度下激活才能具有吸气作用，因此在满足其他部件安全的前提下，它的激活方法与工艺十分重要。本文通过建立在线激活NEG薄膜的温度分析模型，模拟在加热温度为180 ℃和200 ℃情况下的NEG镀膜真空盒及磁铁的温度分布；采用聚酰亚胺加热膜缠绕管道的加热方式对管道的在线激活工艺进行初步研究，完成银铜（OFS）真空管在线激活时的温度测量，测得磁铁最高温度保持在40 ℃左右，验证了NEG镀膜真空管在线激活时四极磁铁的安全性。此研究为合肥先进光源NEG镀膜真空盒在线激活提供了解决方案和工作基础。Abstract: The Hefei Advanced Light Facility (HALF), which includes an injector and a Diffraction Limited Storage Ring (DLSR), needs ultrahigh vacuum environment to satisfy the lifetime of beam. The small-diameter vacuum chamber coated with NEG (Non-Evaporable Getter) not only saves space, but also has a high pumping speed, which can well meet the demand of obtaining ultra-high vacuum in diffraction-limited devices. The NEG films need to be activated at a certain temperature to get the pumping speed. Therefore, the NEG film activation method and process is important to ensure the safety of the other system components, such as the magnets. Based on the appropriate activation temperature of the coated NEG films, a temperature analysis model was applied to simulate the temperature distribution of the NEG coated vacuum chamber and the magnet during in-situ activation at the temperatures of 180 ℃ and 200 ℃, respectively. The oxygen-free silver bearing copper (OFS) vacuum tubes were baked out by polyimide (PI) heaters and the temperature of the tube and the magnet pole was measured. The maximum temperature measured at the magnet pole was about 40 ℃, which confirmed the safety of the quadrupole magnet. This work will be a solution and basis of in-situ activation of the NEG-coated vacuum chamber in the Hefei Advanced Light Facility.
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图 2 真空管位于不同偏心位置时四极磁铁最高温度的变化
Figure 2. Maximum temperature of quadrupole magnet changes with different decentered parameter
图 4 NEG激活实验系统加热过程中温度变化图
Figure 4. Diagram of temperature change during heating of NEG activation experiment system
表 1 材料热传导系数
Table 1. Thermal conductivity of materials
material thermal conductivity/(W·m−1·℃−1) air 5×10−3 magnet 20 OFS 391 PI 0.31 
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表 2 银铜管(包裹7层镀铝PI薄膜)加热功率表
Table 2. Heating power of OFS tube
OFS temperature/℃ magnet temperature/℃ power/W power density/(W·cm−1) 132.4 35.0 120.7 1.4 167.1 39.4 166.6 1.9 180.0 38.9 193.8 2.2 207.5 40.7 226.5 2.6
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表 3 铜管与四极磁铁温度
Table 3. Temperature of quadrupole magnet and OFS tube
No. room temperature/℃ measure temperature/℃ FEA temperature/℃ 1 24.8 38.7 37.6 2 24.8 41.3 40.5 3 24.8 36.2 35.0
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