Accelerator grid structural and electron backstreaming failures are the most important factors affecting the ion thruster＇s lifetime.During the thruster＇s operation,Charge Exchange Xenon（CEX） ions are generated fr...Accelerator grid structural and electron backstreaming failures are the most important factors affecting the ion thruster＇s lifetime.During the thruster＇s operation,Charge Exchange Xenon（CEX） ions are generated from collisions between plasma and neutral atoms.Those CEX ions grid＇s barrel and wall frequently,which cause the failures of the grid system.In order to validate whether the 20 cm Lanzhou Ion Propulsion System（LIPS-200） satisfies China＇s communication satellite platform＇s application requirement for North-South Station Keeping（NSSK）,this study analyzed the measured depth of the pit/groove on the accelerator grid＇s wall and aperture diameter＇s variation and estimated the operating lifetime of the ion thruster.Different from the previous method,in this paper,the experimental results after the 5500 h of accumulated operation of the LIPS-200 ion thruster are presented firstly.Then,based on these results,theoretical analysis and numerical calculations were firstly performed to predict the on-orbit lifetime of LIPS-200.The results obtained were more accurate to calculate the reliability and analyze the failure modes of the ion thruster.The results indicated that the predicted lifetime of LIPS-200＇s was about 13218.1 h which could satisfy the required lifetime requirement of 11000 h very well.展开更多
Langevin simulation of the particles multi-passing over the saddle point is proposed to calculate thermal fission rate. Due to finite friction and the corresponding thermal fluctuation, a backstreaming exists in the p...Langevin simulation of the particles multi-passing over the saddle point is proposed to calculate thermal fission rate. Due to finite friction and the corresponding thermal fluctuation, a backstreaming exists in the process of the particle descent from the saddle to the scission. This leads to that the diffusion behind the saddle point has influence upon the stationary flow across the saddle point. A dynamical correction factor, as a ratio of the flows of multi- and first-overpassing the saddle point, is evaluated analytically. The results show that the fission rate calculated by the particles multi-passing over the saddle point is lower than the one calculated by the particle firstly passing over the saddle point, and the former approaches the results at the scission point.展开更多
Foreshock ultralow frequency (ULF) waves constitute a significant physical phenomenon in the plasma environment of terrestrial planets. The occurrence of these waves, associated with backstreaming particles reflected ...Foreshock ultralow frequency (ULF) waves constitute a significant physical phenomenon in the plasma environment of terrestrial planets. The occurrence of these waves, associated with backstreaming particles reflected and accelerated at the bow shock, implies specific conditions and properties of the shock and its foreshock. Using magnetic field and ion measurements from MAVEN, we report a clear event of ULF waves in the Martian foreshock. The interplanetary magnetic field connected to the Martian bow shock, forming a shock angle of ~51°. Indicating that this was a fast mode wave is the fact that ion density varied in phase with perturbations of the wave field. The peak frequency of the waves was about 0.040 Hz in the spacecraft frame, much lower than the local proton gyrofrequency (~0.088 Hz). The ULF waves had a propagation angle approximately 34° from ambient magnetic field and were accompanied by the whistler mode. The ULF waves displayed left-hand elliptical polarization with respect to the interplanetary magnetic field in the spacecraft frame. All these properties fit very well with foreshock waves excited by interactions between solar wind and backstreaming ions through right-hand beam instability.展开更多
文摘Accelerator grid structural and electron backstreaming failures are the most important factors affecting the ion thruster＇s lifetime.During the thruster＇s operation,Charge Exchange Xenon（CEX） ions are generated from collisions between plasma and neutral atoms.Those CEX ions grid＇s barrel and wall frequently,which cause the failures of the grid system.In order to validate whether the 20 cm Lanzhou Ion Propulsion System（LIPS-200） satisfies China＇s communication satellite platform＇s application requirement for North-South Station Keeping（NSSK）,this study analyzed the measured depth of the pit/groove on the accelerator grid＇s wall and aperture diameter＇s variation and estimated the operating lifetime of the ion thruster.Different from the previous method,in this paper,the experimental results after the 5500 h of accumulated operation of the LIPS-200 ion thruster are presented firstly.Then,based on these results,theoretical analysis and numerical calculations were firstly performed to predict the on-orbit lifetime of LIPS-200.The results obtained were more accurate to calculate the reliability and analyze the failure modes of the ion thruster.The results indicated that the predicted lifetime of LIPS-200＇s was about 13218.1 h which could satisfy the required lifetime requirement of 11000 h very well.
基金The project supported by National Natural Science Foundation of China under Grant Nos.10075007 and 10235020
文摘Langevin simulation of the particles multi-passing over the saddle point is proposed to calculate thermal fission rate. Due to finite friction and the corresponding thermal fluctuation, a backstreaming exists in the process of the particle descent from the saddle to the scission. This leads to that the diffusion behind the saddle point has influence upon the stationary flow across the saddle point. A dynamical correction factor, as a ratio of the flows of multi- and first-overpassing the saddle point, is evaluated analytically. The results show that the fission rate calculated by the particles multi-passing over the saddle point is lower than the one calculated by the particle firstly passing over the saddle point, and the former approaches the results at the scission point.
基金supported by the National Key Research and Development Program of China (2016YFB0501300, 2016YFB0501304)the National Natural Science Foundation of China (Grants No.41774187, 41674168, 41774176)+2 种基金Beijing Municipal Science and Technology Commission (Grant No.Z191100004319001)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDA14040404)the pre-research Project on Civil Aerospace Technologies No.D020103 funded by CNSA
文摘Foreshock ultralow frequency (ULF) waves constitute a significant physical phenomenon in the plasma environment of terrestrial planets. The occurrence of these waves, associated with backstreaming particles reflected and accelerated at the bow shock, implies specific conditions and properties of the shock and its foreshock. Using magnetic field and ion measurements from MAVEN, we report a clear event of ULF waves in the Martian foreshock. The interplanetary magnetic field connected to the Martian bow shock, forming a shock angle of ~51°. Indicating that this was a fast mode wave is the fact that ion density varied in phase with perturbations of the wave field. The peak frequency of the waves was about 0.040 Hz in the spacecraft frame, much lower than the local proton gyrofrequency (~0.088 Hz). The ULF waves had a propagation angle approximately 34° from ambient magnetic field and were accompanied by the whistler mode. The ULF waves displayed left-hand elliptical polarization with respect to the interplanetary magnetic field in the spacecraft frame. All these properties fit very well with foreshock waves excited by interactions between solar wind and backstreaming ions through right-hand beam instability.
