Application Research Of NEG Film-Coated Vacuum Chambers For HALF Vacuum System

With the continuous development of synchrotron radiation technology and the user’s demand for higher brightness light source,the fourth generation of light source is developing rapidly in the worldwide.The vacuum chamber with small aperture and limited pump space of the fourth-generation light source vacuum system lead to difficult exhaust and large local gas load.The scattering of relativistic electrons and residual gas becomes the main limit for the beam life.The magnetron sputtering method is used for plating of NEG(Non-evaporable Getter)film inside the vacuum chamber.Through high temperature activation,such a NEG film is changed to the pumping surface.It has a very low PSD(Photon Stimulated Desorption),ESD(Electron Stimulated Desorption)and SEY(Secondary Electronic Yield).NEG coating technology has gradually become the fourth generation of light source vacuum system to achieve ultra-high vacuum key technology.Based on the copper materials used in the construction of the HALF(Hefei Advanced Light Facility)vacuum system,different cleaning processes are used to clean different copper materials.Different methods were used to explore the influence of alkaline washing and storage time on the final cleaning effect.The results showed that alkaline washing had little effect on the surface element content of copper,and pickling and passivation would greatly reduce the carbon content on the surface of copper and increase the surface copper content.After cleaning,the surface copper content of CuCrZr,OFC(oxygen-free copper)and OFS Cu(oxygen-free silver-bearing copper)are 49.1%,45.3%and 41%,respectively.As the storage time increases,carbon pollution will gradually increase on the surface of copper.A magnetron sputtering coating device was designed and built for narrow vacuum chamber to perform coating experiments on OFS Cu and CuCrZr pipes with high thermal conductivity and high conductivity.In this project,a pumping performance test platform based on TPMC(Test Particle Monte-carlo)model is constructed.The probability of NEG film adhesion is simulated by theoretical calculation and Molflow+software.The pumping performance of NEG films based on OFS Cu and CuCrZr was tested.When the test gas was CO,adhesion coefficients of NEG films based on OFS Cu and CuCrZr were 0.12 and 0.075,respectively.The saturation of CO in films based on OFS Cu and CuCrZr were 2.63 and 1.79 molecular layers,respectively.Both films show good pumping performance.To get enough NEG coated chambers in schedule for HALF,a multi-chamber coating system was employed,and some multicoating research was performed based on previous work.Through this system,two vacuum chambers were Successfully coated NEG film at the same time.By characterizing the materials of thin film samples with different chambers,the results show that the surface morphology,cross-sectional morphology,surface roughness,and composition of the film coated by different chambers are almost the same.After activation at 180℃ for 2 h,the high oxidation state of the surface metal was transferred to a low oxidation state or metallic state,which indicates that the NEG film is activated.Three NEG coated chambers were equipped with SIP to simulate work status.After activation at 180℃ for 24 h,the pressure inside the chambers was 4.13×10-8 Pa,which reached 2.78×10-8 Pa after about two months.To avoid the pulsed magnetic field of the impact magnet on the metal vacuum chamber to produce a strong eddy current effect,the vacuum chamber here needs to employ a ceramic vacuum chamber coated with a layer of metal film.In order to verify the feasibility of the ceramic pipe coated with metal shielding sputtering coating,we built a magnetron sputter device with ceramic pipes placed inside a vacuum chamber and successfully plated NEG film and Ti film on the small aperture ceramic pipe.By changing the pulse DC magnetron sputtering coating parameters,a series of films samples were obtained.The effects of different coating parameters on thin films were explored through sample characterization.The results show that by using TiZrV alloy wire as the sputtering target,NEG film with balanced element ratio and better surface quality can be obtained,and faster film deposition rate can be obtained by reducing the coating air pressure and increasing the DC pulse frequency.The conductivity of Ti film is better than that of TiZrV type NEG film.