低温永磁波荡器过冷液氮冷却系统的设计

Development of sub-cooled liquid nitrogen cooling system for CPMU

低温永磁波荡器(Cryogenic Permanent Magnet Undulator,CPMU)是目前插入件技术发展的主要方向之一,其利用一些永磁材料,如钕铁硼(Nd Fe B)或镨铁棚(Pr Fe B)的磁场性能在低温下明显高于室温的特性来提高波荡器性能和光源束流品质,工作温区为50-150 K,需要冷却系统的冷却。CPMU冷却系统主要包括过冷液氮冷却系统和磁体阵列冷却回路。本文介绍了上海光源(Shanghai Synchrotron Radiation Facility,SSRF)CPMU过冷液氮冷却系统的设计方案和设计参数,进行了系统主要热负载的分析;对冷却系统中关键设备之一的过冷换热器进行了设计,并计算分析了过冷氮流经CPMU冷却系统的全程阻力损失,为系统另一关键设备液氮泵的选型提供依据。对CPMU过冷液氮冷却系统进行的在线测试表明,该设计满足CPMU样机的冷却需求。

Background： The cryogenic permanent magnet undulator （CPMU） is one of the development trends of the insertion technology. The CPMU, made of NdFeB or PrFeB materials, has a better magnetic field performance at low temperature than that at room temperature. The operating temperature of the CPMU is in the range of 50-150 K up to the magnetic material to be adopted. The CPMU cooling system mainly consists of the CPMU sub-cooled liquid nitrogen cooling system and the CPMU magnet array cooling loop. Purpose： This study aims to develop the CPMU sub-cooled liquid nitrogen （SLN2） cooling system. Methods： According to the design scheme and design parameters of the first CPMU SLN2 cooling system for the Shanghai synchrotron radiation facility （SSRF）, the heat loads of the system were calculated. The sub-cooled heat exchanger, one of the key components of the SLN2 system was designed. The flow resistance of the sub-cooled liquid nitrogen going through the whole CPMU cooling system was calculated, which provides the design base for liquid nitrogen recirculation pump.Results ＆ Conclusion： The first CPMU, made of NdFeB material, and its SLN2 cooling system were installed at SSRF since August, 2016. Online test results showed that the SLN2 system met the CPMU cooling requirements and run stably.