SPT Lifetime Improvement Method Based On The Sputtering Resistance Of Diamond

Compared with the conventional propulsion system,electric propulsion system has advantages of small volume,light quality,and long lifetime.With the development of space technology,the exploration of deep space has been broadened,and there are more requirements for electric propulsion,such as the lifetime of electric propulsion should reach to 15000 hours.The stationary plasma thruster is a kind of mature electric propulsion with simple structure,reliable performance and high specific impulse,but lifetime of them is usually no more than 10000 hours.So it is necessary to adopt effective methods to improve their lifetime to meet the requirements of space exploration.The lifetime of SPT is mainly limited by sputtering corrosion rate of channel wall.When the sputtering corrosion depth is more than the thickness of wall,the magnetic pole under the wall will be exposed to plasma flow,the electromagnetic field in SPT discharge channel will change,so the thruster unable to maintain steady state and its life will be end.There are two methods to extend the lifetime of SPT:1)to control the movement of ions in channel,reduce their bombardment to channel wall;2)to improve the sputtering resistance of wall,slow down its corrosion rate.Generally,the first method needs to change the structure of thruster,and redesign the magnetic field of SPT.As for second method,there is no need to redesign the thruster,and suitable for the existing type of SPT.This paper is based on the second method,choose diamond as the channel wall material,study its sputtering resistance and the effect of lifetime improvement.The weight loss method is used to measure the sputtering yield of diamond.The experiment is under condition of different incident angle of Xe+,and the measurement results are compared to BN ceramic.Results show that the sputtering yield of diamond is less than BN ceramic under different incident angle,and decrease relatively 60%.According to the experiment data,the relationship between sputtering yield and incident angle has been established.Scanning electron microscopy?SEM?is used to observe surface morphology of diamond and BN ceramic.After sputtering,the BN ceramic originally covered by diamond film will have convex structure with large length to diameter radio on its surface.And this convex structure can improve the sputtering resistance of BN ceramic.So the BN ceramic surface can be considered to be coated with diamond,it is not only mean to add a protected layer,but also can affect the sputtering resistance of original wall.PIC/DSMC/MCC method and sputtering relationship were used to simulate the profile change of the diamond wall in SPT-70,and the simulation results are compared to the change of BN ceramic wall.Results show that the max corrosion depth in BN wall is greater than the wall thickness after 3000h sputtering.But at the same time,the max corrosion depth in diamond wall is only 1/3 of wall thickness,and the corrosion rate is very small after3000h(corrosion depth changes by 1×10^-2mm order per 1000h),so the diamond wall can continue to bear sputtering for more time.The simulation result also show that only 1mm thick diamond can bear sputtering for 5000h,but only 300⁴00h for 1 mm thick BN ceramic.So the lifetime of SPT-70with only 1 mm thickness diamond wall can at least reach to 5000h,increase relatively by 67%,so the lifetime improvement effect is remarkable.