Experimental Study On TiZrV Films Deposited By DC Magnetron Sputtering On The Inner Wall Of Slender Pipes

The upgrading of China spallation neutron source(CSNS)project puts forward higher requirements for the vacuum of the accelerator vacuum pipeline,so as to reduce the beam loss and electron multiplication in the pipeline.Most vacuum pipes of the accelerator are slender pipes.Due to the restriction of their flow guide,getting vacuum by adding vacuum pump at both ends of the pipeline will cause a larger pressure gradient in the pipe,and this way is difficult to reach high vacuum.Coating non-evaporable getter(NEG)film on the inner wall of pipeline is the main method to solve this problem.NEG film is generally composed of three elements:Ti,Zr and V.The activation temperature of TiZrV film is low,and it has great suction performance.In order to prepare uniform TiZrV film in the vacuum pipe of accelerator and make the pipe fulfill the average vacuum requirements of CSNS upgrading project,the following research has been presented in this article:Based on the investigation of the previous methods of coating NEG film in the vacuum cavity,the characteristics of various methods of coating were compared.Considering the uniformity of the film thickness on the inner wall of the pipeline and keeping the proportion of the target elements,the method of DC magnetron sputtering was adopted to coat the TiZrV film in the vacuum pipeline of the accelerator.Simplifying the modeling and simulating of the experimental system by COMSOL,which verify the feasibility of magnetron sputtering coating in a slender pipe.It is found that there is a difference of the discharge state between both ends of the pipe and the middle part of the pipe.In order to reduce the influence of this difference on the uniformity of film thickness,the two ends of the target can be extended into the auxiliary vacuum chamber.The results of the glow discharge experiment show that when the magnetic field strength is 300 GS,the experimental system has a high deposition rate;the magnetic field strength is 300 GS and the vacuum degree range is 5-9 PA,which can maximize the utilization of discharge power.The experiment of coating TiZrV film on the inner wall of the pipeline was carried out,and the coating samples were tested and analyzed.The TiZrV film with thickness of 1-2?m was obtained on the inner wall of the pipeline after 12 hours of coating under the condition of 300 Gs,7 Pa,200 mA and 100?,and the film morphology was columnar structure,which was favorable for gas adsorption and internal diffusion.The results of pumping rate test show that the NEG pipe can be activated at 180?,but the pumping rate is smaller than that of 225?-250?.In the limit pressure test of NEG pipeline,it is confirmed that the limit pressure has reached 2 × 10-8 Pa,which is required by the project.