Application Research Of Low Activation Temperature Non-evaporable Getter Film In Large Particle Accelerator

In the future,the diffraction limit storage ring of Hefei Advanced Light Source(HALF)has a magnet aperture much smaller than that of traditional accelerators to generate a high-gradient focusing magnetic field.However,this will cause the aperture of various types of vacuum chambers to be much smaller than that of the third-generation light source.The traditional centralized pumping method cannot meet the vacuum requirements of the small-aperture vacuum chamber of the HALF diffraction limit storage ring and the compact multiple bend achromat structure design.In order to solve this problem,a uniform non-evaporable getter(NEG)film is deposited on the surface of the vacuum chamber by magnetron sputtering to reduce the outgassing rate of the inner wall.After in-situ activation,the wall of the vacuum chamber can be changed from a degassing source to a pumping surface,so that the inside of the vacuum chamber pipe has a uniform pumping speed.The use of NEG film has many advantages compared with the traditional centralized pumping method:it effectively improves the vacuum distribution in the storage ring and therefore reduces the longitudinal gradient of the pressure inside the vacuum chamber;it meets the pumping requirements of the small-aperture vacuum chamber;it improve the beam life and the machine stability.However,the activation temperature of the commonly used TiZrV NEG film is usually in the range of 180-400?.In addition,the activation temperature will gradually increase as the number of activations increases.It is very complicated to heat a hundreds-meter-long storage ring vacuum chamber to a temperature of nearly 200? or even higher.This process also greatly increases the construction cost of the system and brings great challenges to the later maintenance of the diffraction-limited storage ring.At the same time,vacuum chambers made of metal alloys such as copper,aluminum and stainless steel will be damaged.In order to maintain the mechanical integrity of the vacuum chamber and prolong the instrument life of the chamber,it is important to reduce the activation temperature of the NEG film.The lower activation temperature can also simplify the heating and activation procedures,simplify the vacuum system design,reduce thermal expansion,and increase the selectivity of materials and components.Based on the requirements of the HALF storage ring vacuum chamber for the NEG coating process,a magnetron sputtering coating device suitable for small aperture vacuum chambers was built.By adjusting the film preparation process parameters(working pressure,discharge current,working gas,etc.),cathode target material and substrate material,TiZrV films with different microstructure characteristics and new TiZrHfV films are prepared.This paper uses X-ray photoelectron spectroscopy(XPS),Scanning electron microscope,X-ray diffraction,Energy dispersive X-Ray spectroscopy,Atomic force microscopy and other material characterization methods to test the properties of different films,including surface and internal composition,surface and cross-sectional morphology,grain structure and size,element distribution and content,and roughness.The effects of different coating parameters and targets on the basic properties of the film are summarized,and the effects of different microstructures on the vacuum performance of the film are analyzed.In-situ XPS was used to detect the activation temperature of the TiZrV film sputtered with different targets,and the activation state of the film under different activation temperatures and annealing durations was analyzed qualitatively and quantitatively.It is verified that the film deposited by the alloy wire has a more uniform composition and a lower activation temperature.Under the same coating parameters,the activation temperature of the film deposited by the alloy wire is about 20? lower than that of the film deposited by the twisted wire.It is verified that a longer annealing time greatly improves the activation degree of the film.The activation process of TiZrHfV film was detected by XPS method for the first time.Under the same coating parameters and conditions,the activation temperature of TiZrHfV film was about 20?lower than that of TiZrV film.Based on previous accumulation of similar experience,the best parameters of HALF vacuum chamber coating are obtained.Small-aperture pipes were deposited on the newly built coating device.The adhesion rate test system was designed and built.Using TPMC model and MOLFLOW+software,the adhesion rate of the copper-silver pipe deposited with NEG film was tested for the first time,and the activation temperature of NEG film was verified again.The related research results provide a theoretical basis for the practical application of the ultra-high vacuum technology of the HALF diffraction limit storage ring,and lay a solid foundation and strong support for the design and construction of a new generation of diffraction limit storage ring engineering.