Previous studies have shown that there is an obvious coupling relationship between the installation location of the external cathode and the magnetic separatrix in the plume region of a Hall thruster.In this paper,the...Previous studies have shown that there is an obvious coupling relationship between the installation location of the external cathode and the magnetic separatrix in the plume region of a Hall thruster.In this paper,the particle-in-cell simulation method is used to compare the thruster discharge process under the conditions of different position relationships between the cathode and the magnetic separatrix.By comparing the distribution of electron conduction,potential,plasma density and other microscopic parameters,we try to explain the formation mechanism of the discharge difference.The simulation results show that the cathode inside and outside the magnetic separatrix has a significant effect on the distribution of potential and plasma density.When the cathode is located on the outer side of the magnetic separatrix,the potential above the plume region is relatively low,and there is a strong potential gradient above the plume region.This potential gradient is more conducive to the radial diffusion of ions above the plume,which is the main reason for the strong divergence of the plume.The distribution of ion density is also consistent with the distribution of potential.When the cathode is located on the outer side of the magnetic separatrix,the radial diffusion of ions in the plume region is enhanced.Meanwhile,by comparing the results of electron conduction,it is found that the traiectories of electrons emitted from the cathode are significantly different between the inner and outer sides of the magnetic separatrix.This is mainly because the electrons are affected by the magnetic mirror effect of the magnetic tip,which makes it difficult for the electrons to move across the magnetic separatrix.This is the main reason for the difference in potential distribution.In this paper,the simulation results of macroscopic parameters under several conditions are also compared,and they are consistent with the experimental results.The cathode is located on the inner side of the magnetic separatrix,which can effectively reduce the plume divergence angle and improve the thrust.In this paper,the cathode moves from R=50 mm to R=35 mm along the radial direction,the thrust increases by 3.6 mN and the plume divergence angle decreases by 23.77%.Combined with the comparison of the ionization region and the peak ion density,it is found that the main reason for the change in thrust is the change in the radial diffusion of ions in the plume region.展开更多
Hall thrusters have been widely used in orbit correction and the station-keeping of geostationary satellites due to their high specific impulse, long life, and high reliability. During the operating life of a Hall thr...Hall thrusters have been widely used in orbit correction and the station-keeping of geostationary satellites due to their high specific impulse, long life, and high reliability. During the operating life of a Hall thruster, high-energy ions will bombard the discharge channel and cause serious erosion. As time passes, this sputtering process will change the macroscopic surface morphology of the discharge channel, especially near the exit, thus affecting the performance of the thruster.Therefore, it is necessary to carry out research on the motion of the sputtering products and erosion process of the discharge wall. To better understand the moving characteristics of sputtering products, based on the hybrid particle-in-cell（PIC） numerical method, this paper simulates the different erosion states of the thruster discharge channel in different moments and analyzes the moving process of different particles, such as B atoms and B~＋ ions. In this paper,the main conclusion is that B atoms are mainly produced on both sides of the channel exit, and B~＋ ions are mainly produced in the middle of the channel exit. The ionization rate of B atoms is approximately 1%.展开更多
In this work,we have carried out a simulation study on the discharge process of Hall thrusters under the conditions of different neutral gas radial supply positions based on the particle-in-cell(PIC)and Monte Carlo co...In this work,we have carried out a simulation study on the discharge process of Hall thrusters under the conditions of different neutral gas radial supply positions based on the particle-in-cell(PIC)and Monte Carlo collision(MCC)methods.This paper compares the two-dimensional(2D)distributions of neutral gas,plasma and wall erosion-related parameters under different neutral gas supply positions.The comparison results show that the change of the neutral gas supply position affects the radial distribution uniformity of the neutral gas and plasma in the channel.From the comparison of the density peaks,it can be found that the neutral gas density and the plasma density peak under the upper gas supply condition are relatively low,and the plasma density peak is 22.49%lower than the density peak under the middle gas supply condition.Meanwhile,as the radial position of the gas supply moves from the lower gas supply to the upper gas supply,the position of the ionization zone also gradually moves toward the anode.The results of erosion-related parameter distribution comparison show that the change of gas supply location has an obvious influence on erosion rate and erosion range.In terms of erosion rate,the wall erosion rate is relatively low under the upper gas supply condition,and the peak erosion rates of the inner and outer walls are 33.3%and 29.9%lower than those under the other two conditions.In terms of erosion range,as the gas supply position moves from the lower gas supply position to the upper gas supply position,the erosion range gradually increases from5 to 7.5 mm.展开更多
Prokaryotic Argonautes(pAgos)provide bacteria and archaea with immunity against plasmids and viruses.Catalytically active pAgos utilize short oligonucleotides as guides to directly cleave foreign nucleic acids,while i...Prokaryotic Argonautes(pAgos)provide bacteria and archaea with immunity against plasmids and viruses.Catalytically active pAgos utilize short oligonucleotides as guides to directly cleave foreign nucleic acids,while inactive pAgos lacking catalytic residues employ auxiliary effectors,such as nonspecific nucleases,to trigger abortive infection upon detection of foreign nucleic acids.Here,we report a unique group of catalytically active pAgo proteins that frequently associate with a phos-pholipase D(PLD)family protein.We demonstrate that this particular system employs the catalytic center of the associated PLD protein rather than that of pAgo to restrict plasmid DNA,while interestingly,its immunity against a single-stranded DNA virus relies on the pAgo catalytic center and is enhanced by the PLD protein.We also find that this system selectively suppresses viral DNA propagation without inducing noticeable abortive infection outcomes.Moreover,the pAgo protein alone enhances gene editing,which is unexpectedly inhibited by the PLD protein.Our data highlight the ability of catalytically active pAgo proteins to employ auxiliary proteins to strengthen the targeted eradication of different genetic invaders and underline the trend of PLD nucleases to participate in host immunity.展开更多
基金supported by the Shanghai 2022 Science and Technology Innovation Action Plan(No.22YF1446800)。
文摘Previous studies have shown that there is an obvious coupling relationship between the installation location of the external cathode and the magnetic separatrix in the plume region of a Hall thruster.In this paper,the particle-in-cell simulation method is used to compare the thruster discharge process under the conditions of different position relationships between the cathode and the magnetic separatrix.By comparing the distribution of electron conduction,potential,plasma density and other microscopic parameters,we try to explain the formation mechanism of the discharge difference.The simulation results show that the cathode inside and outside the magnetic separatrix has a significant effect on the distribution of potential and plasma density.When the cathode is located on the outer side of the magnetic separatrix,the potential above the plume region is relatively low,and there is a strong potential gradient above the plume region.This potential gradient is more conducive to the radial diffusion of ions above the plume,which is the main reason for the strong divergence of the plume.The distribution of ion density is also consistent with the distribution of potential.When the cathode is located on the outer side of the magnetic separatrix,the radial diffusion of ions in the plume region is enhanced.Meanwhile,by comparing the results of electron conduction,it is found that the traiectories of electrons emitted from the cathode are significantly different between the inner and outer sides of the magnetic separatrix.This is mainly because the electrons are affected by the magnetic mirror effect of the magnetic tip,which makes it difficult for the electrons to move across the magnetic separatrix.This is the main reason for the difference in potential distribution.In this paper,the simulation results of macroscopic parameters under several conditions are also compared,and they are consistent with the experimental results.The cathode is located on the inner side of the magnetic separatrix,which can effectively reduce the plume divergence angle and improve the thrust.In this paper,the cathode moves from R=50 mm to R=35 mm along the radial direction,the thrust increases by 3.6 mN and the plume divergence angle decreases by 23.77%.Combined with the comparison of the ionization region and the peak ion density,it is found that the main reason for the change in thrust is the change in the radial diffusion of ions in the plume region.
文摘Hall thrusters have been widely used in orbit correction and the station-keeping of geostationary satellites due to their high specific impulse, long life, and high reliability. During the operating life of a Hall thruster, high-energy ions will bombard the discharge channel and cause serious erosion. As time passes, this sputtering process will change the macroscopic surface morphology of the discharge channel, especially near the exit, thus affecting the performance of the thruster.Therefore, it is necessary to carry out research on the motion of the sputtering products and erosion process of the discharge wall. To better understand the moving characteristics of sputtering products, based on the hybrid particle-in-cell（PIC） numerical method, this paper simulates the different erosion states of the thruster discharge channel in different moments and analyzes the moving process of different particles, such as B atoms and B~＋ ions. In this paper,the main conclusion is that B atoms are mainly produced on both sides of the channel exit, and B~＋ ions are mainly produced in the middle of the channel exit. The ionization rate of B atoms is approximately 1%.
文摘In this work,we have carried out a simulation study on the discharge process of Hall thrusters under the conditions of different neutral gas radial supply positions based on the particle-in-cell(PIC)and Monte Carlo collision(MCC)methods.This paper compares the two-dimensional(2D)distributions of neutral gas,plasma and wall erosion-related parameters under different neutral gas supply positions.The comparison results show that the change of the neutral gas supply position affects the radial distribution uniformity of the neutral gas and plasma in the channel.From the comparison of the density peaks,it can be found that the neutral gas density and the plasma density peak under the upper gas supply condition are relatively low,and the plasma density peak is 22.49%lower than the density peak under the middle gas supply condition.Meanwhile,as the radial position of the gas supply moves from the lower gas supply to the upper gas supply,the position of the ionization zone also gradually moves toward the anode.The results of erosion-related parameter distribution comparison show that the change of gas supply location has an obvious influence on erosion rate and erosion range.In terms of erosion rate,the wall erosion rate is relatively low under the upper gas supply condition,and the peak erosion rates of the inner and outer walls are 33.3%and 29.9%lower than those under the other two conditions.In terms of erosion range,as the gas supply position moves from the lower gas supply position to the upper gas supply position,the erosion range gradually increases from5 to 7.5 mm.
基金This work was supported by the Science&Technology Fundamental Resources Investigation Program(2022FY101100)the Strategic Priority Research Program of the Chinese Academy of Sciences(Precision seed design and breeding)(XDA24020101)+4 种基金the National Natural Science Foundation of China(Nos.31970544,31970545,32022003,32150020,32200057,and 32270092)the Youth Innovation Promotion Association of CAS(No.2020090)the China National Postdoctoral Program for Innovative Talents(BX20220331)the China Postdoctoral Science Foundation(2022M720160)the Special Research Assistant Program of Chinese Academy of Sciences(No.2023000056).
文摘Prokaryotic Argonautes(pAgos)provide bacteria and archaea with immunity against plasmids and viruses.Catalytically active pAgos utilize short oligonucleotides as guides to directly cleave foreign nucleic acids,while inactive pAgos lacking catalytic residues employ auxiliary effectors,such as nonspecific nucleases,to trigger abortive infection upon detection of foreign nucleic acids.Here,we report a unique group of catalytically active pAgo proteins that frequently associate with a phos-pholipase D(PLD)family protein.We demonstrate that this particular system employs the catalytic center of the associated PLD protein rather than that of pAgo to restrict plasmid DNA,while interestingly,its immunity against a single-stranded DNA virus relies on the pAgo catalytic center and is enhanced by the PLD protein.We also find that this system selectively suppresses viral DNA propagation without inducing noticeable abortive infection outcomes.Moreover,the pAgo protein alone enhances gene editing,which is unexpectedly inhibited by the PLD protein.Our data highlight the ability of catalytically active pAgo proteins to employ auxiliary proteins to strengthen the targeted eradication of different genetic invaders and underline the trend of PLD nucleases to participate in host immunity.
