Impurity Control And Particles Exhausting Via The Advanced Vacuum Technology On Tokamaks

In the tokamak device,the application and development of vacuum technology provide a clean vacuum environment and wall conditions for the vacuum chambers of the tokamak to meet the needs of plasma discharge and efficient operation of the device.In this work,we focus on the key issues in the vacuum operation of tokamak,such as the fuel particles exhausting,the mass separation between deuterium and helium,and the impurity particles removal.And the independent and related research is carried out based on the above requirements.The research results have been presented as follows.In terms of vacuum technology development,the research on the mass separation between deuterium and helium has been carried out,aiming at broadening the pressure measurement range of deuterium-helium gas and measurement technology on EAST.The gas has the different ionization probability under the ionization energies of 40 eV and 70 eV for deuterium and helium.Based on this properity of SRS-RGA200 residual gas analyzer,the indirect measurement is developed to distinguish deuterium or helium from their mixture.And the applicable range covers a deuterium content of 1～100%and the total pressure range of 10-6～10-2 Pa.It was successfully applied to the measurement of deuterium removal rate during He-GDC by the new vacuum measurement technology.And the removal rate data is obtained under the different cleaning currents.In general,the research provides a cost-effective vacuum measurement technology which is suitable for medium vacuum,high vacuum and ultra-high vacuum environment in the tokamak.The research on the impurity removal by vacuum surface cleaning technology and vacuum surface coating technology is carried out towards the fast recovery of vacuum conditions and plasma discharge after the vacuum failure in EAST.It is believed that about 19.5 g water and 27.5 g hydrogen impurities are removed after vacuum failure,with the help of baking and discharge cleaning.And the background vacuum reaches 3.0×10-6 Pa,which meet the requirement of plasma operation.The PWI process is also effectively suppressed with the help of lithium coating and the accumulated plasma duration of 1700 s in 3 days.The hydrogen-deuterium ratio is decreased to the grade of 0.2.Then,the stable plasma discharges are re-established and the plasma fast recovery is assisted to achieve after the vacuum failure.Meanwhile,the experimental result shows that the carbon impurities which directly cause tungsten sputtering is decreased about 80%.And the evolution of tungsten intensity decreases by-60%.And the active control of tungsten impurities and the plasma recovery could be achieved by strong wall-conditionings.The research results further confirm the significant effect of lithiation on tungsten impurity control,which has great contributed on the long-pulse plasma operation in EAST.In addition,the vacuum technologies are comprehensively applied in the development of the Material Sputtering Experimental Device which is defined as a platform for the comparative and parallel experiments with the EAST tokamak.And the development of the plasma source,diagnostics system,pumping system,wall-conditionings system and magnet coils are achieved by vacuum pumping technology,vacuum measurement technology,vacuum surface cleaning technology and vacuum coating technology.The operation results show that the device has the advantages of flexible parameter adjustment,and its ultra-high vacuum could reach 10-5 Pa.The steady-state magnetic field could operate at 0.63 T.The electron temperature of the central plasma is 1～10 eV,and the electron density is in the range of 1018～1020 m-3.The successful development of the device would provide an important scientific tool for studying the fusion material and wall-conditioning technology.It would be of great value in promoting the research of PWI.In general,the advanced vacuum technologies such as particle exhausting,vacuum measurement,vacuum surface cleaning and material coating have been widely used in the tokamak research.This paper has carried out the application research of vacuum technology in the impurities control and particles exhausting on the tokamak.The source of impurities in EAST is clearly discussed.And the active control of impurities source is achieved by the integrated use of various wall-conditionings,which improves the ultra-high vacuum and wall conditions for plasma operation.Meanwhile,the research on the particle exhausting improvement and the mass separation technology between deuterium and helium provide powerful scientific means to improve the capability of high-parameter,long-pulse plasma operation on EAST.Furthermore,the results provide the reference for future fusion reactors and the development of large-scale vacuum systems.