Plasma in the discharge channel of a pulsed plasma thruster(PPT) with flared electrodes is simulated by a self-developed two-dimensional code. The fully particle-in-cell method with Monte Carlo collision is employed t...Plasma in the discharge channel of a pulsed plasma thruster(PPT) with flared electrodes is simulated by a self-developed two-dimensional code. The fully particle-in-cell method with Monte Carlo collision is employed to model the particle movement and collisions and investigate the plasma properties and acceleration process. Temporal and spatial variations of the electron density distribution and the ion velocity between electrodes are calculated and analyzed in detail.The computational results of the electron number density, which is in the order of 1023 m-3,show good agreements with experimental results of a PPT named ADD SIMP-LEX. The ion velocity distributions along the center line of the channel lead to a comprehensive understanding of ions accelerated by electromagnetic field. The electron distributions of PPT with discharge voltages varying from 1300 to 2000 V are compared. The diffusion of electrons presents strong dependency on discharge voltage and implies higher degree of ionization for higher voltage.展开更多
The E×B drift instability is studied in Hall thruster using one-dimensional particle in cell(PIC)simulation method.By using the dispersion relation,it is found that unstable modes occur only in discrete bands in ...The E×B drift instability is studied in Hall thruster using one-dimensional particle in cell(PIC)simulation method.By using the dispersion relation,it is found that unstable modes occur only in discrete bands in k space at cyclotron harmonics.The results indicate that the number of unstable modes increases by increasing the external electric field and decreases by increasing the radial magnetic field.The ion mass does not affect the instability wavelength.Furthermore,the results confirm that there is an instability with short wavelength and high frequency.Finally,it is shown that the electron and ion distribution functions deviate from the initial state and eventually the instability is saturated by ion trapping in the azimuthal direction.Also for light mass ion,the frequency and phase velocity are very high that could lead to high electron mobility in the axial direction.展开更多
A two-dimensional PIC/MCC model is developed to simulate the nitrogen radio frequency hollow cathode discharge（rf-HCD）.It is found that both the sheath oscillation heating and the secondary electron heating together...A two-dimensional PIC/MCC model is developed to simulate the nitrogen radio frequency hollow cathode discharge（rf-HCD）.It is found that both the sheath oscillation heating and the secondary electron heating together play a role to maintain the rf-HCD under the simulated conditions.The mean energy of ions（N＋_2,N＋）in the negative glow region is greater than the thermal kinetic energy of the molecular gas（N2）,which is an important characteristic of rf-HCD.During the negative portion of the hollow electrode voltage cycle,electrons mainly follow pendulum movement and produce a large number of ionization collisions in the plasma region.During the positive voltage of the rf cycle,the axial electric field becomes stronger and its direction is pointing to the anode（substrate）,therefore the ions move toward the anode（substrate）via the axial electric field acceleration.Compared with dc-HCD,rf-HCD is more suitable for serving as a plasma jet nozzle at low pressure.展开更多
Numerical simulations by the code of Object-Oriented PIC （Particle-in-Cell） and the Monte Carlo Collision （MCC） method were carried out in order to obtain an insight into the characteristics of plasmas generated b...Numerical simulations by the code of Object-Oriented PIC （Particle-in-Cell） and the Monte Carlo Collision （MCC） method were carried out in order to obtain an insight into the characteristics of plasmas generated by glow discharges in low pressure helium in a four-anode DC glow discharge device. The results show that, the pressure, the external mirror magnetic field, and the virtual breadth of the annular electrode affect the radial distribution of the plasma density and temperature. The simulations are instructive for further experiments.展开更多
In this study,we computationally examined the dynamics of dielectric barrier discharge in hydrogen sulfide.The simulations were performed with a 1 d3 v particle-in-cell/Monte Carlo collision model in which a parallel-...In this study,we computationally examined the dynamics of dielectric barrier discharge in hydrogen sulfide.The simulations were performed with a 1 d3 v particle-in-cell/Monte Carlo collision model in which a parallel-plate electrode geometry with dielectrics was used.Particle recombination process is represented in the model.The discharge mode was found to be initially Townsend discharge developing from the cathode to the anode,and at the peak of the current,a more stable glow discharge develops from the anode to the cathode.A higher applied voltage results in sufficient secondary electrons to trigger a second current peak,and then the current amplitude increases.As the frequency is increased,it leads to the advance of the phase and an increase in the amplitude of the current peak.A higher dielectric permittivity also makes the discharge occur earlier and more violently in the gap.展开更多
In this paper, we analytically explore the magnetic field and mass density evolutions obtained in particle-in-cell（PIC）and magnetohydrodynamics（MHD） simulations of a rarefied deuterium shell Z-pinch and compare th...In this paper, we analytically explore the magnetic field and mass density evolutions obtained in particle-in-cell（PIC）and magnetohydrodynamics（MHD） simulations of a rarefied deuterium shell Z-pinch and compare those results, and also we study the effects of artificially increased Spitzer resistivity on the magnetic field evolution and Z-pinch dynamic process in the MHD simulation. There are significant differences between the profiles of mass density in the PIC and MHD simulations before 45 ns of the Z-pinch in this study. However, after the shock formation in the PIC simulation,the mass density profile is similar to that in the MHD simulation in the case of using multiplier 2 to modify the Spitzer resistivity. Compared with the magnetic field profiles of the PIC simulation of the shell, the magnetic field diffusion has still not been sufficiently revealed in the MHD simulation even though their convergence ratios become the same by using larger multipliers in the resistivity. The MHD simulation results suggest that the magnetic field diffusion is greatly enhanced by increasing the Spitzer resistivity used, which, however, causes the implosion characteristic to change from shock compression to weak shock, even shockless evolution, and expedites the expansion of the shell. Too large a multiplier is not suggested to be used to modify the resistivity in some Z-pinch applications, such as the Z-pinch driven inertial confinement fusion（ICF） in a dynamic hohlraum. Two-fluid or Hall MHD model, even the PIC/fluid hybrid simulation would be considered as a suitable physical model when there exist the plasma regions with very low density in the simulated domain.展开更多
Continuous microwave propagation through a time-varying plasma and frequency up-conversion has been demonstrated by particle-in-cell (PIC) simulation. In principle, it is possible to transform a 2.45 GHz source radiat...Continuous microwave propagation through a time-varying plasma and frequency up-conversion has been demonstrated by particle-in-cell (PIC) simulation. In principle, it is possible to transform a 2.45 GHz source radiation to an arbitrary larger frequency radiation. The energy conversion is also obtained by the theoretical analysis and has been testified by PIC simulation. The source wave was propagating in a parallel plate waveguide locally filled with the ionized gas. In this paper we would discuss the effects of the rise time, the plasma length, the switching time and the collision frequency on the energy conversion, and the methods to improve the upshift wave energy are proposed. We also put forward the new concept of the critical values of the rise time and the source wave amplitude to provide a theoretical basis for the selection of parameters in the experiments.展开更多
By performing one-dimensional particle-in-cell simulations, the nonlinear effects of electronacoustic(EA) waves are investigated in a multispecies plasma, whose constituents are hot electrons, cold electrons, and beam...By performing one-dimensional particle-in-cell simulations, the nonlinear effects of electronacoustic(EA) waves are investigated in a multispecies plasma, whose constituents are hot electrons, cold electrons, and beam electrons with immobile neutralized positive ions. Numerical analyses have identified that EA waves with a sufficiently large amplitude tend to trap cold electrons. Because EA waves are dispersive, where the wave modes with different wavenumbers have different phase velocities, the trapping may lead to the mixing of cold electrons. The cold electrons finally get thermalized or heated. The investigation also shows that the excited EA waves give rise to a broad range of wave frequencies, which may be helpful for understanding the broadband-electrostatic-noise spectrum in the Earth’s auroral region.展开更多
Stimulated Raman particle-in-cell （PIC） simulations scattering （SRS） in a low-density The backward stimulated Raman plasma slab is investigated by scattering （B-SRS） dominates initially and erodes the head of th...Stimulated Raman particle-in-cell （PIC） simulations scattering （SRS） in a low-density The backward stimulated Raman plasma slab is investigated by scattering （B-SRS） dominates initially and erodes the head of the pump wave, while the forward stimulated Raman scattering （F-SRS） subsequently develops and is located at the rear part of the slab. Two-stage electron acceleration may be more efficient due to the coexistence of these two instabilities. The B-SRS plasma wave with low phase velocities can accelerate the background electrons which may be further boosted to higher energies by the F-SRS plasma wave with high phase velocities. The simulations show that the peaks of the main components in both the frequency and wave number spectra occur at the positions estimated from the phase-matching conditions.展开更多
The electron heating characteristics of magnetic enhancement capacitively coupled argon plasmas in presence of both longitudinal and transverse uniform magnetic field have been explored through both theoretical and nu...The electron heating characteristics of magnetic enhancement capacitively coupled argon plasmas in presence of both longitudinal and transverse uniform magnetic field have been explored through both theoretical and numerical calculations.It is found that the longitudinal magnetic field can affect the heating by changing the level of the pressure heating along the longitudinal direction and that of the Ohmic heating along the direction which is perpendicular to both driving electric field and the applied transverse magnetic field,and a continuously increased longitudinal magnetic field can induce pressure heating to become dominant.Moreover,the electron temperature as well as proportion of some low energy electrons will increase if a small longitudinal magnetic field is introduced,which is attributed to the increased average electron energy.We believe that the research will provide guidance for optimizing the magnetic field configuration of some discharge systems having both transverse and longitudinal magnetic field.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 11602016)
文摘Plasma in the discharge channel of a pulsed plasma thruster(PPT) with flared electrodes is simulated by a self-developed two-dimensional code. The fully particle-in-cell method with Monte Carlo collision is employed to model the particle movement and collisions and investigate the plasma properties and acceleration process. Temporal and spatial variations of the electron density distribution and the ion velocity between electrodes are calculated and analyzed in detail.The computational results of the electron number density, which is in the order of 1023 m-3,show good agreements with experimental results of a PPT named ADD SIMP-LEX. The ion velocity distributions along the center line of the channel lead to a comprehensive understanding of ions accelerated by electromagnetic field. The electron distributions of PPT with discharge voltages varying from 1300 to 2000 V are compared. The diffusion of electrons presents strong dependency on discharge voltage and implies higher degree of ionization for higher voltage.
文摘The E×B drift instability is studied in Hall thruster using one-dimensional particle in cell(PIC)simulation method.By using the dispersion relation,it is found that unstable modes occur only in discrete bands in k space at cyclotron harmonics.The results indicate that the number of unstable modes increases by increasing the external electric field and decreases by increasing the radial magnetic field.The ion mass does not affect the instability wavelength.Furthermore,the results confirm that there is an instability with short wavelength and high frequency.Finally,it is shown that the electron and ion distribution functions deviate from the initial state and eventually the instability is saturated by ion trapping in the azimuthal direction.Also for light mass ion,the frequency and phase velocity are very high that could lead to high electron mobility in the axial direction.
基金supported by Natural Science Foundation of Hebei Province,China(No.A2012205072)
文摘A two-dimensional PIC/MCC model is developed to simulate the nitrogen radio frequency hollow cathode discharge（rf-HCD）.It is found that both the sheath oscillation heating and the secondary electron heating together play a role to maintain the rf-HCD under the simulated conditions.The mean energy of ions（N＋_2,N＋）in the negative glow region is greater than the thermal kinetic energy of the molecular gas（N2）,which is an important characteristic of rf-HCD.During the negative portion of the hollow electrode voltage cycle,electrons mainly follow pendulum movement and produce a large number of ionization collisions in the plasma region.During the positive voltage of the rf cycle,the axial electric field becomes stronger and its direction is pointing to the anode（substrate）,therefore the ions move toward the anode（substrate）via the axial electric field acceleration.Compared with dc-HCD,rf-HCD is more suitable for serving as a plasma jet nozzle at low pressure.
文摘Numerical simulations by the code of Object-Oriented PIC （Particle-in-Cell） and the Monte Carlo Collision （MCC） method were carried out in order to obtain an insight into the characteristics of plasmas generated by glow discharges in low pressure helium in a four-anode DC glow discharge device. The results show that, the pressure, the external mirror magnetic field, and the virtual breadth of the annular electrode affect the radial distribution of the plasma density and temperature. The simulations are instructive for further experiments.
基金supported by National Natural Science Foundation of China(Nos.21503279,51777164,and 52077169)the Fundamental Research Funds for the Central Universities,China(Nos.xtr042019009 and PY3A083)HPC Platform,Xi’an Jiaotong University。
文摘In this study,we computationally examined the dynamics of dielectric barrier discharge in hydrogen sulfide.The simulations were performed with a 1 d3 v particle-in-cell/Monte Carlo collision model in which a parallel-plate electrode geometry with dielectrics was used.Particle recombination process is represented in the model.The discharge mode was found to be initially Townsend discharge developing from the cathode to the anode,and at the peak of the current,a more stable glow discharge develops from the anode to the cathode.A higher applied voltage results in sufficient secondary electrons to trigger a second current peak,and then the current amplitude increases.As the frequency is increased,it leads to the advance of the phase and an increase in the amplitude of the current peak.A higher dielectric permittivity also makes the discharge occur earlier and more violently in the gap.
基金Projected supported by the National Natural Science Foundation of China(Grant Nos.11675025,11135007,and 11405012)
文摘In this paper, we analytically explore the magnetic field and mass density evolutions obtained in particle-in-cell（PIC）and magnetohydrodynamics（MHD） simulations of a rarefied deuterium shell Z-pinch and compare those results, and also we study the effects of artificially increased Spitzer resistivity on the magnetic field evolution and Z-pinch dynamic process in the MHD simulation. There are significant differences between the profiles of mass density in the PIC and MHD simulations before 45 ns of the Z-pinch in this study. However, after the shock formation in the PIC simulation,the mass density profile is similar to that in the MHD simulation in the case of using multiplier 2 to modify the Spitzer resistivity. Compared with the magnetic field profiles of the PIC simulation of the shell, the magnetic field diffusion has still not been sufficiently revealed in the MHD simulation even though their convergence ratios become the same by using larger multipliers in the resistivity. The MHD simulation results suggest that the magnetic field diffusion is greatly enhanced by increasing the Spitzer resistivity used, which, however, causes the implosion characteristic to change from shock compression to weak shock, even shockless evolution, and expedites the expansion of the shell. Too large a multiplier is not suggested to be used to modify the resistivity in some Z-pinch applications, such as the Z-pinch driven inertial confinement fusion（ICF） in a dynamic hohlraum. Two-fluid or Hall MHD model, even the PIC/fluid hybrid simulation would be considered as a suitable physical model when there exist the plasma regions with very low density in the simulated domain.
基金supported by National Natural Science Foundation of China(Nos.51677145,11622542 and U1537210)
文摘Continuous microwave propagation through a time-varying plasma and frequency up-conversion has been demonstrated by particle-in-cell (PIC) simulation. In principle, it is possible to transform a 2.45 GHz source radiation to an arbitrary larger frequency radiation. The energy conversion is also obtained by the theoretical analysis and has been testified by PIC simulation. The source wave was propagating in a parallel plate waveguide locally filled with the ionized gas. In this paper we would discuss the effects of the rise time, the plasma length, the switching time and the collision frequency on the energy conversion, and the methods to improve the upshift wave energy are proposed. We also put forward the new concept of the critical values of the rise time and the source wave amplitude to provide a theoretical basis for the selection of parameters in the experiments.
基金the support from Chinese Academy of Science(CAS)TWAS for his Ph.D studies at the University of Science and Technology of China in the category of a 2016 CAS-TWAS President’s Fellowship Awardee(Series No.2016-172)+1 种基金partially supported by National Natural Science Foundation of China(Nos.41331067,41774169,and 41527804)the Key Research Program of Frontier Sciences,CAS(QYZDJ-SSW-DQC010)
文摘By performing one-dimensional particle-in-cell simulations, the nonlinear effects of electronacoustic(EA) waves are investigated in a multispecies plasma, whose constituents are hot electrons, cold electrons, and beam electrons with immobile neutralized positive ions. Numerical analyses have identified that EA waves with a sufficiently large amplitude tend to trap cold electrons. Because EA waves are dispersive, where the wave modes with different wavenumbers have different phase velocities, the trapping may lead to the mixing of cold electrons. The cold electrons finally get thermalized or heated. The investigation also shows that the excited EA waves give rise to a broad range of wave frequencies, which may be helpful for understanding the broadband-electrostatic-noise spectrum in the Earth’s auroral region.
基金supported by National High Technology ICF Committee in Chinathe National Natural Science Fund of China(Nos.10675024,10335020,10375011 and 10576007)the Laboratory of Computational Physics(No.51479050205ZW0905)
文摘Stimulated Raman particle-in-cell （PIC） simulations scattering （SRS） in a low-density The backward stimulated Raman plasma slab is investigated by scattering （B-SRS） dominates initially and erodes the head of the pump wave, while the forward stimulated Raman scattering （F-SRS） subsequently develops and is located at the rear part of the slab. Two-stage electron acceleration may be more efficient due to the coexistence of these two instabilities. The B-SRS plasma wave with low phase velocities can accelerate the background electrons which may be further boosted to higher energies by the F-SRS plasma wave with high phase velocities. The simulations show that the peaks of the main components in both the frequency and wave number spectra occur at the positions estimated from the phase-matching conditions.
基金supported by National Natural Science Foundation of China (Nos. 11975163 and 12175160)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘The electron heating characteristics of magnetic enhancement capacitively coupled argon plasmas in presence of both longitudinal and transverse uniform magnetic field have been explored through both theoretical and numerical calculations.It is found that the longitudinal magnetic field can affect the heating by changing the level of the pressure heating along the longitudinal direction and that of the Ohmic heating along the direction which is perpendicular to both driving electric field and the applied transverse magnetic field,and a continuously increased longitudinal magnetic field can induce pressure heating to become dominant.Moreover,the electron temperature as well as proportion of some low energy electrons will increase if a small longitudinal magnetic field is introduced,which is attributed to the increased average electron energy.We believe that the research will provide guidance for optimizing the magnetic field configuration of some discharge systems having both transverse and longitudinal magnetic field.
