Coaxial plasma guns are a type of plasma source that produces plasma which propagates radially and axially controlled by the shape of the ground electrode, which has attracted much interest in several applications. In...Coaxial plasma guns are a type of plasma source that produces plasma which propagates radially and axially controlled by the shape of the ground electrode, which has attracted much interest in several applications. In this work, a 120° opening angle of CPG nozzle is used as a plasma gun configuration that operates at the energy of 150 J. The ionization of polyethylene insulator between the electrodes of the gun produces a cloud of hydrogen and carbon plasma.The triple Langmuir probe and Faraday cup are used to measure plasma density and plasma temperature. These methods are used to measure the on-axis and off-axis plasma divergence of the coaxial plasma gun. The peak values of ion densities measured at a distance of 25 mm on-axis from the plasma gun are(1.6±0.5)×10^(19)m^(-3)and(2.8±0.6)×10^(19)m^(-3)for hydrogen and carbon plasma respectively and the peak temperature is 3.02±0.5 eV. The mean propagation velocity of plasma is calculated using the transit times of plasma at different distances from the plasma gun and is found to be 4.54±0.25 cm/μs and 1.81±0.18 cm/μs for hydrogen and carbon plasma respectively. The Debye radius is obtained from the measured experimental data that satisfies the thin sheath approximation. The shot-to-shot stability of plasma parameters facilitates the use of plasma guns in laboratory experiments. These types of plasma sources can be used in many applications like plasma opening switches, plasma devices, and as plasma sources.展开更多
Ce:YIG thin films are taken as an ideal candidate for magneto-optical devices with giant Faraday effect in the near-infrared range,but it is hindered by a limited Ce^(3+)/Ce^(4+)ratio and a high saturation driving fie...Ce:YIG thin films are taken as an ideal candidate for magneto-optical devices with giant Faraday effect in the near-infrared range,but it is hindered by a limited Ce^(3+)/Ce^(4+)ratio and a high saturation driving field.To address this issue,Eu doping can increase the Faraday rotation angle by ~40% to 1.315×10^(4)deg/cm and decrease the saturation driving field by ~38%to 1.17 kOe in Eu_(0.75)Ce_(1)Y_(1.25)Fe_(5)O_(12 )compared to Ce_(1)Y_(2)Fe_(5)O_(12)pristine.The mechanism is attributed to the conversion of Ce^(4+)to Ce^(3+)and the weakening of ferrimagnetism by Eu doping.This work not only provides strategies for improving Ce^(3+)/Ce^(4+) ratio in Ce:YIG,but also develops(Eu,Ce):YIG with a promising Faraday rotation angle for magneto-optical devices.展开更多
The accurate knowledge of the thrust vector eccentricity and beam divergence characteristics of Hall thrusters are of significant engineering value for the beneficial integration and successful application of Hall thr...The accurate knowledge of the thrust vector eccentricity and beam divergence characteristics of Hall thrusters are of significant engineering value for the beneficial integration and successful application of Hall thrusters on spacecraft.For the characteristics of the plume bipolar diffusion due to the annular discharge channel of the Hall thruster,a Gaussian-fitted method for thrust vector deviation angle and beam divergence of Hall thrusters based on dual Faraday probe array planes was proposed in respect of the Hall thruster beam characteristics.The results show that the ratios of the deviation between the maximum and minimum values of the beam divergence angle and the thrust vector eccentricity angle using a Gaussian fit to the optimized Faraday probe dual plane to the mean value are 1.4%and 11.5%,respectively.The optimized thrust vector eccentricity angle obtained has been substantially improved,by approximately 20%.The beam divergence angle calculated using a Gaussian fitting to the optimized Faraday probe dual plane is approximately identical to the non-optimized one.The beam divergence and thrust vector eccentricity angles for different anode mass flow rates were obtained by averaging the beam divergence and thrust vector eccentricity angles calculated by the dual-plane,Gaussian-fitted ion current density method for different cross-sections.The study not only allows for an immediate and effective tool for determining the design of thrust vector adjustment mechanisms of spacecraft with different power Hall thrusters but also for characterizing the 3D spatial distribution of the Hall thruster plume.展开更多
The inverse Faraday effect(IFE),which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma,has rarely been studied for...The inverse Faraday effect(IFE),which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma,has rarely been studied for lasers with unconventional polarization states.In this paper,IFE is reconsidered for weakly relativistic full Poincarébeams,which can contain all possible laser polarization states.Starting from cold electron fluid equations and the conservation of generalized vorticity,a self-consistent theoretical model combining the nonlinear azimuthal current and diamagnetic current is presented.The theoretical results show that when such a laser propagates in a plasma,an azimuthally varying quasi-static axial magnetic field can be generated,which is quite different from the circularly polarized case.These results are qualitatively and quantitatively verified by three-dimensional particle-in-cell simulations.Our work extends the theoretical understanding of the IFE and provides a new degree of freedom in the design of magnetized plasma devices.展开更多
Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes.Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic ins...Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes.Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulator Mn Bi2Te4.We find that by breaking the combined mirror symmetries with either perpendicular electric field or external magnetic moment,Kerr and Faraday effects occur.Under perpendicular electric field,antiferromagnetic topological insulators(AFMTI)show sharp peaks at the interband transition threshold,whereas trivial insulators show small adjacent positive and negative peaks.Gate voltage and Fermi energy can be tuned to reveal the differences between AFMTI and trivial insulators.We find that AFMTI with large antiferromagnetic order can be proposed as a pure magneto-optical rotator due to sizable Kerr(Faraday)angles and vanishing ellipticity.Under external magnetic moment,AFMTI and trivial insulators are significantly different in the magnitude of Kerr and Faraday angles and ellipticity.For the qualitative behaviors,AFMTI shows distinct features of Kerr and Faraday angles when the spin configurations of the system change.These phenomena provide new possibilities to optically detect and manipulate the layered topological antiferromagnets.展开更多
针对35 kHz超声激励薄液膜形成的Faraday波,采用实验和有限元仿真,对Faraday波的形成机理进行探究。建立超声激励下的两相流计算模型,采用计算流体力学(CFD)方法对Faraday波的形成过程进行有限元仿真,通过分析相图和流线图,探讨Faraday...针对35 kHz超声激励薄液膜形成的Faraday波,采用实验和有限元仿真,对Faraday波的形成机理进行探究。建立超声激励下的两相流计算模型,采用计算流体力学(CFD)方法对Faraday波的形成过程进行有限元仿真,通过分析相图和流线图,探讨Faraday波的形成机理,得到Faraday波的振动频率约为超声激励频率的1/2。液体惯性的存在,导致超声激励与液体表面波存在不断变化的相位差,相位差变化周期约等于2个超声激励周期。通过35 k Hz超声激励薄液膜实验,在薄液膜表面观察到排列整齐的Faraday波图案,通过测量Faraday波的波长,得出实验获得的Faraday波频率约为超声激励频率的1/2,与有限元仿真结果一致。展开更多
基金supported by Bhabha Atomic Research Centre, Department of Atomic Energy, Government of IndiaDepartment of Atomic Energy, Government of India for financial assistance under DAE Doctoral Fellowship Scheme-2018。
文摘Coaxial plasma guns are a type of plasma source that produces plasma which propagates radially and axially controlled by the shape of the ground electrode, which has attracted much interest in several applications. In this work, a 120° opening angle of CPG nozzle is used as a plasma gun configuration that operates at the energy of 150 J. The ionization of polyethylene insulator between the electrodes of the gun produces a cloud of hydrogen and carbon plasma.The triple Langmuir probe and Faraday cup are used to measure plasma density and plasma temperature. These methods are used to measure the on-axis and off-axis plasma divergence of the coaxial plasma gun. The peak values of ion densities measured at a distance of 25 mm on-axis from the plasma gun are(1.6±0.5)×10^(19)m^(-3)and(2.8±0.6)×10^(19)m^(-3)for hydrogen and carbon plasma respectively and the peak temperature is 3.02±0.5 eV. The mean propagation velocity of plasma is calculated using the transit times of plasma at different distances from the plasma gun and is found to be 4.54±0.25 cm/μs and 1.81±0.18 cm/μs for hydrogen and carbon plasma respectively. The Debye radius is obtained from the measured experimental data that satisfies the thin sheath approximation. The shot-to-shot stability of plasma parameters facilitates the use of plasma guns in laboratory experiments. These types of plasma sources can be used in many applications like plasma opening switches, plasma devices, and as plasma sources.
基金supported by the National Science Fund for Distinguished Young Scholars (Grant No. 52225201)the National Natural Science Foundation of China (Grant Nos. 52072085 and 52271207)+3 种基金the National Key Research and Development Program of China (Grant No. 2023YFE0201000)the Fundamental Research Funds for the Central Universities (Grant No. HIT.BRET.2022001)the Heilongjiang Touyan Innovation Team Programthe Science Foundation of National Key Laboratory of Science and Technology on Advanced Composites in Special Environments。
文摘Ce:YIG thin films are taken as an ideal candidate for magneto-optical devices with giant Faraday effect in the near-infrared range,but it is hindered by a limited Ce^(3+)/Ce^(4+)ratio and a high saturation driving field.To address this issue,Eu doping can increase the Faraday rotation angle by ~40% to 1.315×10^(4)deg/cm and decrease the saturation driving field by ~38%to 1.17 kOe in Eu_(0.75)Ce_(1)Y_(1.25)Fe_(5)O_(12 )compared to Ce_(1)Y_(2)Fe_(5)O_(12)pristine.The mechanism is attributed to the conversion of Ce^(4+)to Ce^(3+)and the weakening of ferrimagnetism by Eu doping.This work not only provides strategies for improving Ce^(3+)/Ce^(4+) ratio in Ce:YIG,but also develops(Eu,Ce):YIG with a promising Faraday rotation angle for magneto-optical devices.
基金the Key Laboratory Funds for Science and Technology on Vacuum Technology and Physics Laboratory(No.HTKJ2022KL510002)the Military Test Instruments Program(No.2006ZCTF0054)。
文摘The accurate knowledge of the thrust vector eccentricity and beam divergence characteristics of Hall thrusters are of significant engineering value for the beneficial integration and successful application of Hall thrusters on spacecraft.For the characteristics of the plume bipolar diffusion due to the annular discharge channel of the Hall thruster,a Gaussian-fitted method for thrust vector deviation angle and beam divergence of Hall thrusters based on dual Faraday probe array planes was proposed in respect of the Hall thruster beam characteristics.The results show that the ratios of the deviation between the maximum and minimum values of the beam divergence angle and the thrust vector eccentricity angle using a Gaussian fit to the optimized Faraday probe dual plane to the mean value are 1.4%and 11.5%,respectively.The optimized thrust vector eccentricity angle obtained has been substantially improved,by approximately 20%.The beam divergence angle calculated using a Gaussian fitting to the optimized Faraday probe dual plane is approximately identical to the non-optimized one.The beam divergence and thrust vector eccentricity angles for different anode mass flow rates were obtained by averaging the beam divergence and thrust vector eccentricity angles calculated by the dual-plane,Gaussian-fitted ion current density method for different cross-sections.The study not only allows for an immediate and effective tool for determining the design of thrust vector adjustment mechanisms of spacecraft with different power Hall thrusters but also for characterizing the 3D spatial distribution of the Hall thruster plume.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant No.11975014the Strategic Priority Research Program of Chinese Academy of Sciences under Grant Nos.XDA25050400 and XDA25010200.
文摘The inverse Faraday effect(IFE),which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma,has rarely been studied for lasers with unconventional polarization states.In this paper,IFE is reconsidered for weakly relativistic full Poincarébeams,which can contain all possible laser polarization states.Starting from cold electron fluid equations and the conservation of generalized vorticity,a self-consistent theoretical model combining the nonlinear azimuthal current and diamagnetic current is presented.The theoretical results show that when such a laser propagates in a plasma,an azimuthally varying quasi-static axial magnetic field can be generated,which is quite different from the circularly polarized case.These results are qualitatively and quantitatively verified by three-dimensional particle-in-cell simulations.Our work extends the theoretical understanding of the IFE and provides a new degree of freedom in the design of magnetized plasma devices.
基金Project supported by the National Natural Science Foundation of China(Grant No.11904062)the Starting Research Fund from Guangzhou University(Grant No.RQ2020076)Guangzhou Basic Research Program,jointed funded by Guangzhou University(Grant No.202201020186)。
文摘Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes.Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulator Mn Bi2Te4.We find that by breaking the combined mirror symmetries with either perpendicular electric field or external magnetic moment,Kerr and Faraday effects occur.Under perpendicular electric field,antiferromagnetic topological insulators(AFMTI)show sharp peaks at the interband transition threshold,whereas trivial insulators show small adjacent positive and negative peaks.Gate voltage and Fermi energy can be tuned to reveal the differences between AFMTI and trivial insulators.We find that AFMTI with large antiferromagnetic order can be proposed as a pure magneto-optical rotator due to sizable Kerr(Faraday)angles and vanishing ellipticity.Under external magnetic moment,AFMTI and trivial insulators are significantly different in the magnitude of Kerr and Faraday angles and ellipticity.For the qualitative behaviors,AFMTI shows distinct features of Kerr and Faraday angles when the spin configurations of the system change.These phenomena provide new possibilities to optically detect and manipulate the layered topological antiferromagnets.
文摘针对35 kHz超声激励薄液膜形成的Faraday波,采用实验和有限元仿真,对Faraday波的形成机理进行探究。建立超声激励下的两相流计算模型,采用计算流体力学(CFD)方法对Faraday波的形成过程进行有限元仿真,通过分析相图和流线图,探讨Faraday波的形成机理,得到Faraday波的振动频率约为超声激励频率的1/2。液体惯性的存在,导致超声激励与液体表面波存在不断变化的相位差,相位差变化周期约等于2个超声激励周期。通过35 k Hz超声激励薄液膜实验,在薄液膜表面观察到排列整齐的Faraday波图案,通过测量Faraday波的波长,得出实验获得的Faraday波频率约为超声激励频率的1/2,与有限元仿真结果一致。
