| The main challenges on vacuum for next generation particle accelerators with high energy, high intensity, high luminosity and long beam lifetime, are the achievements of ultra high vacuum, lower temperature, high vacuum gradient, electron induced instabilities, and high intensity. These problems have become the research hotspots and need to be solved urgently. Under the support of National Natural Science Foundation,research and characterization of the surface composition, surface morphology and secondary electron emission characteristics, film coating process and surface treatments of vacuum related materials for next generation particle accelerators are explored. The main results are as follows:1. Secondary electron yield is an important characteristic of vacuum related materials for next generation particle accelerator. However, there is no specialized equipment and mature testing methods. We independently developed the first domestic secondary electron characteristic parameters test equipment with high precision, multifunction and high efficiency. This equipment can achieve the functions of secondary electron yield mearurement for conductors or insulators at different temperature (750K-20K), different incident angles (10°? 90°), and different doses. The experimental results show that the functions and test precision of this equipment reach leading level in China and advanced level in the world. Compared with some famous laboratories in the world, it has been demonstrated that this instrument has the advantage of high reliability and precision.2. The first domestic research on secondary electron emission characteristics and the key film coating parameters of non evaporable getters (TiZrV and TiZrV-Pd films) were developed for vacuum chambers of next generation particle accelerators. TiZrV-Pd film has good performances, such as low secondary electron yield, long lifetime and better gases adsorption characteristics. The lowest secondary electron yield of TiZrV film can be reduced to 1.38. The effect of coating parameters on the secondary electron yield of TiZrV-Pd,TiZrV and Pd films was investigated for the first time.3. Using CST software, the author put forward the method to simulate the effect of Ti cathodes with different sizes on the electric field distributions during the film coating on the internal surface of a racetrack-type ceramic pipe by DC magnetron sputtering as the first domestic research, so as to optimize the size and the installation position of Ti plate cathode for the deposition of TiN films.This simulation method greatly improves the uniformity of the TiN film,solving the difficult problem of heterogeneity of thin film coating in the ceramic pipe with special-shaped sections. This simulation method is for optimization of coating device design, cathode size and the location of the cathode. The advantages of this method are cost reduction, time and energy saving, deposition efficiency improvement. In addition, when the Ti wires cathode replaced with the Ti plate cathode, the deposition rate of TiN film was nearly 40 times higher than before.4. Based on the semi empirical formulas of Matsunami model and YT model,the deposition rates of TiZrV and Pd films deposited by magnetron sputtering method were calculated and simulated first in China. And the experimental results and the simulation results were compared which shows that: the deposition rate C can be estimated by sputtering depth D in the magnetron sputtering process of cylindrical pipe coating system for single metal films. By comparing the experimental results and the simulation results, more accurate semi empirical formula for film deposition rate calculation was found.Electron cloud is the most critical problem in the major three challenges for next generation accelerator vacuum system. Therefore, the secondary electron yield characteristic has become an important research content for vacuum related materials.At present, the main mature scheme is to study the secondary electron yield characteristics of vacuum related materials for accelerators and to search for new materials with low secondary electron yield. In this paper, it was studied that the preparation of various new materials with low secondary electron yield. Furthermore,the potential applications were discussed. The main study contents as follows:1. The preparation parameters and the relevant characteristics of TiZrV-Pd and TiN film coating were obtained. Moreover, by using Monte Carol method, the secondary electron emission process for TiZrV-Pd film was simulated, and the factors affecting the secondary electron emission of various materials were analyzed quantitatively.2. Based on the excellent thermal conductivity and high mobility of graphene,the secondary electron yield characteristics of graphene with copper substrate were deeply studied. Also, the application of graphene with low secondary electron yield which can be used in next generation accelerator vacuum system is proposed for the first time.3. Laser treated surface technology can be applied in the atmosphere to etch the surface of the materials by in situ processing. The secondary electron yields of copper and stainless steel samples can be reduced less than 1 after laser treating.As the latest international research frontiers, this technology is suitable for most materials with the advantages of low cost, high repeatability and currently the most promising solution to obtain low secondary electron yield materials. The author firstly carried out a lot of experimental studies and mechanism analysis about the efforts of laser parameters, atmospheric exposure and other factors on the secondary electron yield of laser treated materials in China. The technical problems of laser treated technology for vacuum pipes are discussed and analyzed.These results will be of important reference values for vacuum chamber design of the next generation accelerators, the solutions for surface treatments of vacuum related materials, electron cloud problem of storage rings and the achievements of ultra high vacuum for accelerators. |
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